Currently solving a puzzle and looking for some tips on sorting by events ordered. I would like to know what exactly is the procedure I should be following. Consider this
I input a number, then there n inputs
each input has two events, where of for event1 event2, and event1 happens before event2.
Consider the input
6
Eatfood Cuthair
Eatfood BrushTeeth
School EatFood
School DoHair
DoHair Meeting
Meeting Brushteeth
The output will be
school -> dohair-> eatfood -> meeting -> cuthair -> brushteeth
In that order. Since if we write everything down, school is indeed the first thing that occurs, and then dohair is second. If more than one possible ordering exists simply output one. You may assume that all events are connected in some way, and no circular dependencies exist.
What I am thinking about doing is making two arrays, one which has all eventOne's and all eventTwo's. I'm not really sure where to go from here though. I would like to do this in javascript. Thanks! Any hints or algorithms are suggested
Another Input
6
vote_140_prof announce_140_prof
vote_140_prof first_day_of_classes
dev_shed_algo vote_140_prof
dev_shed_algo do_hair
do_hair big_meeting
big_meeting first_day_of_classes
Output
dev_shed_algo do_hair vote_140_prof big_meeting announce_140_prof first_day_of_classes
I found the solution file on my computer, its in python which I don't know, but hopefully this will help others understand the problem
from collections import defaultdict
def toposort(graph, roots):
res = [i for i in roots]
queue = [i for i in roots]
while queue:
for i in graph[queue.pop(0)]:
if i not in res:
res.append(i)
queue.append(i)
return res
graph = defaultdict(set)
a_set = set()
b_set = set()
for i in range(int(input())):
a, b = input().split()
a_set.add(a)
b_set.add(b)
graph[a].add(b)
print(" ".join(i for i in toposort(graph, a_set - b_set)))
My attempt
var words =
'vote_140_prof announce_140_prof vote_140_prof first_day_of_classes devshed_algo vote_140_prof dev_shed_algo do_hair do_hair big_meeting big_meeting first_day_of_classes';
var events = words;
events = events.split(/\s+/);
console.log(events);
var obj = {};
for (var i = 0 ; i < events.length ; i++)
{
var name = events[i];
if(obj[name] === undefined )
{
obj[name] = [];
}
obj[name].push(events[i%2 === 1 ? i-1 : i+1]);
}
console.log(obj);
FORMATING
function sequenceEvents(pairs){
var edges = pairs.reduce(function(edges,pair){
edges.set(pair[0],[]).set(pair[1],[]);
new Map();
});
pairs.forEach(function(edges,pair){
edges.set(pair[0],[]).set(pair[1],[]);
});
var result = [];
while(edges.size){
var children = new Set([].concat.apply([],[...edges.value()]));
var roots = [...edges.keys()].filter(function(event){
!children.has(event);
});
if(!roots.length) throw "Cycle detected";
roots.forEach(function(root){
result.push(root);
edges.delete(root);
});
}
return result;
}
The Python algorithm is not correct. It will fail for this input:
3
A B
A C
C B
It will output:
A, B, C
...which conflicts with the last rule. This is because it wrongly assumes that the children of any root-event can be safely added to the result, and depend on no other events. In the above case, it will identify A as root, and B and C as its children. Then it will pop of C from that list, and add it to the result, without seeing that C depends on B, which is not in the result yet.
As others have noted, you need to make sure the capitalisation is consistent. Brushteeth and BrushTeeth are considered different events. The same is true for EatFood and Eatfood.
I provide here a solution. I hope the inline comments explain well enough what is happening:
function sequenceEvents(pairs) {
// Create a Map with a key for each(!) event,
// and add an empty array as value for each of them.
var edges = pairs.reduce(
// Set both the left and right event in the Map
// (duplicates get overwritten)
(edges, pair) => edges.set(pair[0], []).set(pair[1], []),
new Map() // Start with an empty Map
);
// Then add the children (dependent events) to those arrays:
pairs.forEach( pair => edges.get(pair[0]).push(pair[1]) );
var result = [];
// While there are still edges...
while (edges.size) {
// Get the end points of the edges into a Set
var children = new Set( [].concat.apply([], [...edges.values()]) );
// Identify the parents, which are not children, as roots
var roots = [...edges.keys()].filter( event => !children.has(event) );
// As we still have edges, we must find at least one root among them.
if (!roots.length) throw "Cycle detected";
roots.forEach(root => {
// Add the new roots to the result, all events they depend on
// are already in the result:
result.push(root);
// Delete the edges that start with these events, since the
// dependency they express has been fulfilled:
edges.delete(root);
});
}
return result;
}
// I/O
var input = document.querySelector('#input');
var go = document.querySelector('#go');
var output = document.querySelector('#output');
go.onclick = function() {
// Get lines from input, ignoring the initial number
// ... then split those lines in pairs, resulting in
// an array of pairs of events
var pairs = input.value.trim().split(/\n/).slice(1)
.map(line => line.split(/\s+/));
var sequence = sequenceEvents(pairs);
output.textContent = sequence.join(', ');
}
Input:<br>
<textarea id="input" rows=7>6
EatFood CutHair
EatFood BrushTeeth
School EatFood
School DoHair
DoHair Meeting
Meeting BrushTeeth
</textarea>
<button id="go">Sequence Events</button>
<div id="output"></div>
Without arrow functions nor apply
As in comments you indicated you like to have the code without arrow functions first:
function sequenceEvents(pairs) {
// Create a Map with a key for each(!) event,
// and add an empty array as value for each of them.
var edges = pairs.reduce(function (edges, pair) {
// Set both the left and right event in the Map
// (duplicates get overwritten)
return edges.set(pair[0], []).set(pair[1], []);
}, new Map() ); // Start with an empty Map
// Then add the children (dependent events) to those arrays:
pairs.forEach(function (pair) {
edges.get(pair[0]).push(pair[1]);
});
var result = [];
// While there are still edges...
while (edges.size) {
// Get the end points of the edges into a Set
var children = new Set(
[...edges.values()].reduce(function (children, value) {
return children.concat(value);
}, [] )
);
// Identify the parents, which are not children, as roots
var roots = [...edges.keys()].filter(function (event) {
return !children.has(event);
});
if (!roots.length) throw "Cycle detected";
roots.forEach(function (root) {
// Add the new roots to the result, all events they depend on
// are already in the result:
result.push(root);
// Delete the edges that start with these events, since the
// dependency they express has been fulfilled:
edges.delete(root);
});
}
return result;
}
Okay. Here's my shot at the problem.
var makePair = function(i0, i1) {
return {start: i0, end: i1};
};
var mp = makePair;
var makeBefores = function(pairs) {
var befores = {};
pairs.forEach(function(pair) {
if (befores[pair.end] == null) {
befores[pair.end] = [pair.start];
} else {
befores[pair.end].push(pair.start);
}
if (befores[pair.start] == null) {
befores[pair.start] = [];
}
});
for (var key in befores) {
console.log("after " + key + "there is:");
for (var i = 0; i < befores[key].length; i++) {
console.log(befores[key][i]);
}
}
return befores;
};
var shouldGoBefore = function(item, before) {
for (var i = 0; i < before.length; i++) {
if (item == before[i]) {
return true;
}
}
return false;
};
var sortEvents = function(pairs) {
if (pairs.length === 0) {
return [];
}
if (pairs.length === 1) {
return [pairs[0].start, pairs[0].end];
}
console.log(pairs);
var befores = makeBefores(pairs);
var sorted = [];
for (var key in befores) {
var added = false;
for (var i = 0; i < sorted.length; i++) {
console.log('checking if ' + sorted[i] + ' should go before ' + befores[key]);
if (shouldGoBefore(sorted[i], befores[key])) {
//console.log("splicing");
sorted.splice(i, 0, key);
added = true;
break;
}
}
if (!added) {
sorted.push(key);
}
}
return sorted.reverse();
}
var pairs = [mp('vote_140_prof','announce_140_prof'),mp('vote_140_prof','first_day_of_classes'),mp('dev_shed_algo','vote_140_prof'),mp('dev_shed_algo','do_hair'),mp('do_hair','big_meeting'),mp('big_meeting','first_day_of_classes'),mp('announce_140_prof','first_day_of_classes')];
console.log(sortEvents(pairs));
One reason things may not have been working is your test data had inconsistent capitalization. The results of this run are:
Array [ "School", "EatFood", "CutHair", "Meeting", "BrushTeeth", "DoHair" ]
I'm going to test it on your other data set but I believe this fulfills the prompt. I'm going to write up how it works in a minute.
Note that this doesn't do any file IO or reading of lines. It takes the input to sortEvents as an array of objects that have a start and end property, which I provided a helper method makePair to create.
The solution works by building a dictionary of what elements go before which others.
If you had an input like:
a->b
c->a
c->b
b->d
The dictionary would be like this:
a->[c],
c->[],
b->[a,c],
d->[b]
Then we use an array as a sort of linked list and we go through it seeing whether we have to insert something. So for example, if we are trying to see where a should be inserted and the list is c, then we would look at the dictionary for c, see that c is in it and then we know that before a there is supposed to be c, therefore we have to insert a after c
Take a hash map start with first event and put it's value to 0 than whenever you encounter event 2 check the value of event 1 in hash than put a smaller value for event 2. Once complete sort hash by value.
Bingo
line = input();
myMap = dict()
i=0
while i < line:
event1 = raw_input()
event2 = raw_input()
if event1 in myMap :
myMap[event2] = myMap[event1]+1
elif event2 in myMap:
myMap[event1] = myMap[event2]-1
else :
myMap[event1] = 0
myMap[event2] = 1
i=i+1
print i
print myMap
I don't know why some people downvoted but yes it's working, Atleast on both your samples
Sample input and output
6
eatfood
cuthair
1
{'eatfood': 0, 'cuthair': 1}
eatfood
brushteeth
2
{'brushteeth': 1, 'eatfood': 0, 'cuthair': 1}
school
eatfood
3
{'brushteeth': 1, 'eatfood': 0, 'school': -1, 'cuthair': 1}
school
dohair
4
{'brushteeth': 1, 'eatfood': 0, 'school': -1, 'cuthair': 1, 'dohair': 0}
dohair
meeting
5
{'school': -1, 'brushteeth': 1, 'cuthair': 1, 'dohair': 0, 'eatfood': 0, 'meeting': 1}
meeting
brushteeth
6
{'school': -1, 'brushteeth': 2, 'cuthair': 1, 'dohair': 0, 'eatfood': 0, 'meeting': 1}
The code is in python, feel free to convert in javascript
Related
I have a Node.js addon written in C++ using Nan. Works fantastically. However, I've not been able to figure out how to have my Node Javascript code pass an arbitrary data object (ex. {attr1:42, attr2:'hi', attr3:[5,4,3,2,1]}) to the C++ addon.
Until now, I've got around this by calling JSON.stringify() on my data object and then parsing the stringified JSON on the C++ side.
Ideally, I'd like to avoid copying data and just get a reference to the data object that I can access, or at least to copy it natively and avoid stringifying/parsing...
Any help would be appreciated!
You can allow your Node.js c++ addons to take arbitrary typed arguments, but you must check and handle the types explicitly. He is a simple example function that shows how to do this:
void args(const Nan::FunctionCallbackInfo<v8::Value>& info) {
int i = 0;
while (i < info.Length()) {
if (info[i]->IsBoolean()) {
printf("boolean = %s", info[i]->BooleanValue() ? "true" : "false");
} else if (info[i]->IsInt32()) {
printf("int32 = %ld", info[i]->IntegerValue());
} else if (info[i]->IsNumber()) {
printf("number = %f", info[i]->NumberValue());
} else if (info[i]->IsString()) {
printf("string = %s", *v8::String::Utf8Value(info[i]->ToString()));
} else if (info[i]->IsObject()) {
printf("[object]");
v8::Local<v8::Object> obj = info[i]->ToObject();
v8::Local<v8::Array> props = obj->GetPropertyNames();
for (unsigned int j = 0; j < props->Length(); j++) {
printf("%s: %s",
*v8::String::Utf8Value(props->Get(j)->ToString()),
*v8::String::Utf8Value(obj->Get(props->Get(j))->ToString())
);
}
} else if (info[i]->IsUndefined()) {
printf("[undefined]");
} else if (info[i]->IsNull()) {
printf("[null]");
}
i += 1;
}
}
To actually solve the problem of handling arbitrary arguments that may contain objects with arbitrary data, I would recommend writing a function that parses an actual object similar to how I parsed function arguments in this example. Keep in mind that you may need to do this recursively if you want to be able to handle nested objects within the object.
You don't have to stringify your object to pass it to c++ addons. There are methods to accept those
arbitary objects. But it is not so arbitary. You have to write different codes to parse the object in c++ .
Think of it as a schema of a database. You can not save different format data in a single collection/table.
You will need another table/collection with the specific schema.
Let's see this example:
We will pass an object {x: 10 , y: 5} to addon, and c++ addon will return another object with sum and product of the
properties like this: {x1:15,y1: 50}
In cpp code :
NAN_METHOD(func1) {
if (info.Length() > 0) {
Local<Object> obj = info[0]->ToObject();
Local<String> x = Nan::New<String>("x").ToLocalChecked();
Local<String> y = Nan::New<String>("y").ToLocalChecked();
Local<String> sum = Nan::New<String>("sum").ToLocalChecked();
Local<String> prod = Nan::New<String>("prod").ToLocalChecked();
Local<Object> ret = Nan::New<Object>();
double x1 = Nan::Get(obj, x).ToLocalChecked()->NumberValue();
double y1 = Nan::Get(obj, y).ToLocalChecked()->NumberValue();
Nan::Set(ret, sum, Nan::New<Number>(x1 + y1));
Nan::Set(ret, prod, Nan::New<Number>(x1 * y1));
info.GetReturnValue().Set(ret);
}
}
In javascript::
const addon = require('./build/Release/addon.node');
var obj = addon.func1({ 'x': 5, 'y': 10 });
console.log(obj); // { sum: 15, prod: 50 }
Here you can only send {x: (Number), y: (number)} type object to addon only. Else it will not be able to parse or
retrieve data.
Like this for the array:
In cpp:
NAN_METHOD(func2) {
Local<Array> array = Local<Array>::Cast(info[0]);
Local<String> ss_prop = Nan::New<String>("sum_of_squares").ToLocalChecked();
Local<Array> squares = New<v8::Array>(array->Length());
double ss = 0;
for (unsigned int i = 0; i < array->Length(); i++ ) {
if (Nan::Has(array, i).FromJust()) {
// get data from a particular index
double value = Nan::Get(array, i).ToLocalChecked()->NumberValue();
// set a particular index - note the array parameter
// is mutable
Nan::Set(array, i, Nan::New<Number>(value + 1));
Nan::Set(squares, i, Nan::New<Number>(value * value));
ss += value*value;
}
}
// set a non index property on the returned array.
Nan::Set(squares, ss_prop, Nan::New<Number>(ss));
info.GetReturnValue().Set(squares);
}
In javascript:
const addon = require('./build/Release/addon.node');
var arr = [1, 2, 3];
console.log(addon.func2(arr)); //[ 1, 4, 9, sum_of_squares: 14 ]
Like this, you can handle data types. If you want complex objects or operations, you just
have to mix these methods in one function and parse the data.
I am attempting to extract JSON values (from structure called jsonWithListOfStatesAndCounters) if it matches with an element in my inputted array (inputedJurisdictionArray). My inputed array contains sting values that include singular or multiple state names (i.e. var inputedJurisdictionArray = ["Iowa", "California, Indiana, Delaware", "Florida"]). The singular State values in this array are handled normally at the end, but the multiple state values is where it gets tricky. I am using split() in order to turn them into another array so they can get processed one by one. Anytime one of the states from this inputed array matches with a "state" value in jsonWithListOfStatesAndCounters, I am extracting it into another JSON structure and pushing it at the end of every block into my initial variable myJurisdictionJSON. The problem I am having is that once these forEach loops are completed, I am still left with my original values in myJurisdictionJSON, instead of the val and counter that should be extracted. The jsonWithListOfStatesAndCounters definitely contains the values that should match with the elements of my inputedJurisdictionArray, but the information is not being pushed into myJurisdictionJSON. What am I doing wrong? Any tips/pointers will be helpful.
var myJurisdictionJSON = [{
jurisdiction_val: 'jurisdiction_val',
jurisdiction_counter: 'jurisdiction_counter'
}];
inputedJurisdictionArray.forEach(function each(item) {
if (Array.isArray(item)) {
item.forEach(each);
} else {
var jurisdictionInput = item;
jsonWithListOfStatesAndCounters.forEach(function each(item) {
if (Array.isArray(item)) {
item.forEach(each);
} else {
if (jurisdictionInput.includes(",") === true){//Checking if more than one jurisdiction in string
var jurisdictionArr = jurisdictionInput.split(", ");
var jurisdictionCounter = item.jurisdictionCounter;
var jurisdictionState = item.jurisdictionState;
jurisdictionArr.forEach(function(element) {
if (myJurisdictionJSON.jurisdiction_counter == 'jurisdiction_counter'){ // If nothing is pushed into our predefined JSON object
if (jurisdictionState.toLowerCase() == trim(element.toLowerCase())) {
var jurisdictionJSON_inner = {
jurisdiction_val: element,
jurisdiction_counter: jurisdictionCounter
};
myJurisdictionJSON.push(jurisdictionJSON_inner);
return;
}
}else if (myJurisdictionJSON.jurisdiction_counter != 'jurisdiction_counter'){ // if an item has been pushed into myJurisdictionJSON, append the next items
var jurisdictionCounter = item.jurisdictionCounter;
var jurisdictionState = item.jurisdictionState;
if (jurisdictionState.toLowerCase() == trim(jurisdictionInput.toLowerCase())) {
jurisdictionJSON_inner.jurisdiction_val = jurisdictionJSON_inner.jurisdiction_val + ", " + jurisdictionInput;
jurisdictionJSON_inner.jurisdiction_counter = jurisdictionJSON_inner.jurisdiction_counter + ", " + jurisdictionCounter;
myJurisdictionJSON.push(jurisdictionJSON_inner);
return;
}
}
});
}
else{// if only one jurisdiction state in jurisdictionInput string
var jurisdictionCounter = item.jurisdictionCounter;
var jurisdictionState = item.jurisdictionState;
if (jurisdictionState.toLowerCase() == trim(jurisdictionInput.toLowerCase())) {
var jurisdictionJSON_inner = {
jurisdiction_val: jurisdictionInput,
jurisdiction_counter: jurisdictionCounter
};
myJurisdictionJSON.push(jurisdictionJSON_inner);
return;
}
}
}
});
I'm not totally sure the output is what you want but it's close.
// input data as per your example
let inputedJurisdictionArray = [
'Iowa',
'California, Indiana, Delaware',
'Florida'
];
// I had to make this part up. It's missing from the example
let jsonWithListOfStatesAndCounters = [{
jurisdictionCounter: 2,
jurisdictionState: 'Florida'
},
{
jurisdictionCounter: 4,
jurisdictionState: 'Indiana'
},
{
jurisdictionCounter: 3,
jurisdictionState: 'Texas'
}
];
// first, fix up inputedJurisdictionArray
// reduce() loops over each array element
// in this case we're actually returning a LARGER
// array instead of a reduced on but this method works
// There's a few things going on here. We split, the current element
// on the ','. Taht gives us an array. We call map() on it.
// this also loops over each value of the array and returns an
// array of the same length. So on each loop, trim() the whitespace
// Then make the accumulator concatenate the current array.
// Fat arrow ( => ) functions return the results when it's one statement.
inputedJurisdictionArray = inputedJurisdictionArray.reduce(
(acc, curr) => acc.concat(curr.split(',').map(el => el.trim())), []
);
// now we can filter() jsonWithListOfStatesAndCounters. Loop through
// each element. If its jurisdictionState property happens to be in
// the inputedJurisdictionArray array, then add it to the
// myJurisdictionJSON array.
let myJurisdictionJSON = jsonWithListOfStatesAndCounters.filter(el =>
inputedJurisdictionArray['includes'](el.jurisdictionState)
);
console.log(myJurisdictionJSON);
So I have a Table made from some json data...
{
"AKH":{
"name": "Amonkhet",
"code": "AKH"
"cards": [
{
"artist": "Izzy",
"cmc": 3,
"colorIdentity": [
"W"
],
"colors": [
"White"
],
"id": "df3a6e0336684c901358f3ff53ec82ff5d7cdb9d",
"imageName": "gideon of the trials",
"layout": "normal",
"loyalty": 3,
"manaCost": "{1}{W}{W}",
"multiverseid": 426716,
"name": "Gideon of the Trials",
"number": "14",
"rarity": "Mythic Rare",
"subtypes": [
"Gideon"
],
"text": "+1: Until your next turn, prevent all damage target permanent would deal.\n0: Until end of turn, Gideon of the Trials becomes a 4/4 Human Soldier creature with indestructible that's still a planeswalker. Prevent all damage that would be dealt to him this turn.\n0: You get an emblem with \"As long as you control a Gideon planeswalker, you can't lose the game and your opponents can't win the game.\"",
"type": "Planeswalker — Gideon",
"types": [
"Planeswalker"
]
},
The Table row ends up looking like this for each of the cards. at the moment I only Attach the ID, Card name, and Mana Cost to each row
<td><a href="#" onclick="showInfo(this.id)"
id="df3a6e0336684c901358f3ff53ec82ff5d7cdb9d">Gideon of the Trials</a></td>
Now I want to search through these cards. (Keep in mind there are over 17,000 different cards that will be on this list) I can get it to find the things.. But I'm having several different issues... Either it finds them all but doesn't hide the rest of the list, or it hides the whole list and only displays one of the found cards.
So question A... What am I missing to make the search work correctly?
$(document).on('change', 'input[type=checkbox]', function() {
var lis = $('.cardsRow')
$('input[type=checkbox]').filter(':checked').each(function(){
filterKeyB = $(this).attr('id')
filterKeyA = $(this).attr('name')
$.each(json, function(setCode, setListing) {
$.each(setListing.cards,function(cardNum, cardListing){
var x = Object.keys(cardListing)
var y = Object.keys(cardListing).map(function (key){
return cardListing[key]
})
for (i = 0; (i < x.length); i++) {
if(x[i] === filterKeyA){
if (y[i] instanceof Array){
var holder = y[i]
var valueArr =[]
for(var k = 0; k < holder.length; k++){
valueArr = holder.join('|').toLowerCase().split('|')
var foundIt = valueArr.includes(filterKeyB)
}
}else{
var stringy = y[i]
var stringyA= stringy.toLowerCase().replace(/\s/g, '')
if (stringyA === filterKeyB){
var foundIt = true
}
}
if(foundIt === true){
$winner = cardListing.name
for (k = 0; (k < lis.length); k++){
if (lis[k].innerText.indexOf($winner) != -1) {
$(lis[k]).show()
}
}
}
}
}
})
Question B... Since you are already here... Would it be better practice to attach the data that can be searched to the element itself? Maybe just the most searched (Like Name and Mana) and have more advanced queries go through the data again?
I don't understand why the code isn't working or even how it works, it looks like it references some functions that aren't defined in the sample. But I can share with you a really simple/intuitive way to filter stuff, I hope you find it useful.
Native filter method is so useful for what you're trying to do, it takes a callback that takes current element as an arg and returns true or false, if true, the element is included in the new array it produces.
But filter only takes one function, and you have many filters, so let's make a function that combines many filter Fns together into one fn, so you can pass them in all at once:
const combineFilters = (...fns) => val => fns.reduce((prev, curr) => prev || curr(val), false);
OK, how about storing the names of the filter functions as keys in an object so we can reference them using a string? That way we could give each checkbox an ID corresponding to the name of the filter function they are supposed to apply, and makes things really easy to implement (and read):
const filterFns = {
startsWithG(card) {
return card.name[0] === 'G';
},
//etc.
};
OK, time to get the IDs of all the checkboxes that are clicked, then map them into an array of functions.
const filters = $('input[type=checkbox]')
.filter(':checked')
.map((e, i) => $(i).attr('id'))
.get()
.map(fnName => filterFns[fnName])
(Assume the relevant data is stored in a var called...data.) We can use combineFilters combined with filters (array of Fns) to activate all of the relevant filters, then map the resulting array of matching objects into the HTML of your choosing.
const matches = data.cards
.filter(combineFilters(...filters))
.map(card => `<div>${card.name}</div>` );
Then time to update DOM with your matches!
As others have noted, if you need to do any more complicated filtering on objects or arrays, lodash library is your friend!
How could I rewrite this code to object javascript. Since Array usage is prohibed, I can only use objects here. Insted of pushing values to array, I would like to push this values into objects.
var container = [];
document.addEventListener("submit", function(e){
e.preventDefault();
});
window.addEventListener("load",function(){
var submit = document.getElementsByClassName("btn-primary");
submit[0].addEventListener("click",add,false);
document.getElementById("pobrisi").addEventListener("click",deleteAll,false);
var dateElement = document.getElementById('datum');
dateElement.valueAsDate = new Date();
var today = new Date();
var dd = today.getDate();
var mm = today.getMonth()+1;
var yyyy = today.getFullYear();
if(dd<10){
dd='0'+dd
}
if(mm<10){
mm='0'+mm
}
today = yyyy+'-'+mm+'-'+dd;
dateElement.setAttribute("min",today);
});
function add() {
var title = document.getElementById("title").value;
var type = document.getElementById("type").value;
var datum = document.getElementById("datum").value.split("-");
datum = datum[2]+". "+datum[1]+". "+datum[0];
var data = new Book(title,type,datum);
container.push(data.add());
display();
}
function display(data) {
var destination = document.getElementById("list");
var html = "";
for(var i =0;i <container.length; i++) {
html +="<li>"+container[i]+"</li>";
}
destination.innerHTML = html;
}
function deleteAll(){
container=[];
document.getElementById("list").innerHTML="";
}
Wondering if is possible to write this code whitout any array usage.
initial remarks
The problem here, in my estimation, is that you haven't learned the fundamentals of data abstraction yet. If you don't know how to implement an array, you probably shouldn't be depending on one quite yet. Objects and Arrays are so widespread because they're so commonly useful. However, if you don't know what a specific data type is affording you (ie, what convenience does it provide?), then it's probable you will be misusing the type
If you take the code here but techniques like this weren't covered in your class, it will be obvious that you received help from an outside source. Assuming the teacher has a curriculum organized in a sane fashion, you should be able to solve problems based on the material you've already covered.
Based on your code, it's evident you really have tried much, but why do you think that people here will come up with an answer that your teacher will accept? How are we supposed to know what you can use?
a fun exercise nonetheless
OK, so (we think) we need an Array, but let's pretend Arrays don't exist. If we could get this code working below, we might not exactly have an Array, but we'd have something that works like an array.
Most importantly, if we could get this code working below, we'd know what it takes to make a data type that can hold a dynamic number of values. Only then can we begin to truly appreciate what Array is doing for us.
// make a list
let l = list(1) // (1)
// push an item on the end
l = push(l, 2) // (1 2)
// push another item on the end
l = push(l, 3) // (1 2 3)
// display each item of the list
listeach(l, function (x) {
console.log(x)
})
// should output
// 1
// 2
// 3
runnable demo
All we have to do is make that bit of code (above) work without using any arrays. I'll restrict myself even further and only use functions, if/else, and equality test ===. I see these things in your code, so I'm assuming it's OK for me to use them too.
But am I supposed to believe your teacher would let you write code like this? It works, of course, but I don't think it brings you any closer to your answer
var empty = function () {}
function isEmpty (x) {
return x === empty
}
function pair (x,y) {
return function (p) {
return p(x,y)
}
}
function head (p) {
return p(function (x,y) {
return x
})
}
function tail (p) {
return p(function (x,y) {
return y
})
}
function push (l, x) {
if (isEmpty(l))
return list(x)
else
return pair(head(l), push(tail(l), x))
}
function list (x) {
return pair(x, empty)
}
function listeach (l, f) {
if (isEmpty(l))
return null
else
(f(head(l)), listeach(tail(l), f))
}
// make a list
let l = list(1) // (1)
// push an item on the end
l = push(l, 2) // (1 2)
// push another item on the end
l = push(l, 3) // (1 2 3)
// display each item of the list
listeach(l, function (x) {
console.log(x)
})
closing remarks
It appears as tho you can use an Object in lieu of an Array. The accepted answer (at this time) shows a very narrow understanding of how an object could be used to solve your problem. After this contrived demonstration, are you confident that you are using Objects properly and effectively?
Do you know how to implement an object? Could you fulfill this contract (below)? What I mean by that, is could you write the functions object, set, and get such that the following expressions evaluated to their expected result?
In case it's not obvious, you're not allowed to use Object to make it happen. The whole point of the exercise is to make a new data type that you don't already have access to
m = object() // m
set(m, key, x) // m
get(m, key) // x
set(m, key2, y) // m
get(m, key2) // y
set(m, key3, set(object(), key4, z)) // m
get(get(m, key3), key4) // z
I'll leave this as an exercise for you and I strongly encourage you to do it. I think you will learn a lot in the process and develop a deep understanding and appreciation for what higher-level data types like Array or Object give to you
Since this is a homework I feel like I shouldn't solve it for you, but rather help you in the right direction.
Like Slasher mentioned you can use objects
With JavaScript object one book would look something like
const book = {
title: 'my awesome title',
type: 'novel'
};
book is the object
title is a property with a value 'my awesome title'
type is a property with a value 'novel'
But objects can also have other objects as values. Something like
const BookShelf= {
Book1: {
Title: 'my awesome title',
Type: 'novel'
},
Book2: {
Title: 'my horrible title',
Type: 'sci-fi'
}
};
You can reference the books in the bookshelf in two ways
const book1 = BookShelf.Book1 // Returns the book1 object
const title1 = Book1.Title; // Get the title
const sametitle = BookShelf.Book1.Title // Returns title for book1, same as above.
You can also use brackets:
const book1 = BookShelf['Book1'];
const title1 = BookShelf['Book1']['Title];
You can even make new properties on a object like this:
const Book3 = {
Title: 'running out of ideas'
Type: 'memoir'
};
BookShelf['Book3'] = Book3;
Now the BookShelf has a Book3 property. So your BookShelf object looks like
const BookShelf= {
Book1: {
Title: 'my awesome title',
Type: 'novel'
},
Book2: {
Title: 'my horrible title',
Type: 'sci-fi'
},
Book3 = {
Title: 'running out of ideas'
Type: 'memoir'
};
};
That should get you started :)
JavaScript Objects is a good way to go
1- define a new object:
var myVar = {};
or
var myVar = new Object();
2- usage
// insert a new value, it doesn't matter if the value is a string or int or even another object
// set a new value
myVar.myFirstValue="this is my first value";
// get existing value and do what ever you want with it
var value = myVar.myFirstValue
I'm brand new to programming so I apologize if this is a simple question.
I had a unique practice problem that I'm not quite sure how to solve:
I'm dealing with two arrays, both arrays are pulled from HTML elements on the page, one array is representing a bunch of states, and the next array is representing their populations. The point of the problem is to print the name of the states and their less than average populations.
To find and print all of the populations that are less than the average I used this code:
function code6() {
// clears screen.
clr();
// both variables pull data from HTML elements with functions.
var pop = getData2();
var states = getData();
var sum = 0;
for( var i = 0; i < pop.length; i++ ){
sum += parseInt( pop[i], 10 );
var avg = sum/pop.length;
if (pop[i] < avg) {
println(pop[i]);
// other functions used in the code to get data, print, and clear the screen.
function getData() {
var dataSource = getElement("states");
var numberArray = dataSource.value.split('\n');
// Nothing to split returns ['']
if (numberArray[0].length > 0) {
return(numberArray);
} else {
return [];
}
}
// Get the data from second data column
function getData2() {
var dataSource = getElement("pops");
var numberArray = dataSource.value.split('\n');
// Nothing to split returns ['']
if (numberArray[0].length > 0) {
return(numberArray);
} else {
return [];
}
}
// Clear the 'output' text area
function clr() {
var out = getElement("output");
out.value = "";
}
// Print to the 'output' HTML element and ADDS the line break
function println(x) {
if (arguments.length === 0) x = '';
print(x + '\n');
}
Now I just need to know how to get the value of these positions within the array so I can pull out the same positions from my states array and display them both side by side. Both arrays have the identical amount of items.
I hope this makes sense and thanks in advance to anyone who has time to take a look at this.
Best regards,
-E
Its a little hard to tell what you are trying to accomplish, but I guess you are going for something like:
'use strict'
function code6() {
const populations = ['39000000', '28000000', '21000000'];
const stateNames = ['california', 'texas', 'florida'];
const states = populations.map((population, i) => ({
'name': stateNames[i],
'population': Number(population),
}));
const sum = states.reduce((sum, state) => sum + state.population, 0);
const average = sum / populations.length;
states
.filter(state => state.population < average)
.forEach(state => {
const name = state.name;
const population = state.population;
console.log(`state name: ${name}, population: ${population}`);
});
}
// run the code
code6();
// state name: texas, population: 28000000
// state name: florida, population: 21000000
I took the liberty of refactoring your code to be a little more modern (es6) and Idiomatic. I hope its not to confusing for you. Feel free to ask any questions about it.
In short you should use:
'use strict' at the top of your files
const/let
use map/filter/forEach/reduce to iterate lists.
use meaningfull names
, and you should avoid:
classic indexed for-loop
parseInt
, and pretty much never ever use:
var
If your states array is built with corresponding indices to your pop one, like this:
states; //=> ['Alabama', 'Alaska', 'Arizona', ...]
pop; //=> [4863300, 741894, 6931071, ...]
then you could simply update your print statement to take that into account:
if (pop[i] < avg) {
println(state[i] + ': ' + pop[i]);
}
Or some such.
However, working with shared indices can be a very fragile way to use data. Could you rethink your getData and getData2 functions and combine them into one that returns a structure more like this the following?
states; //=> [
// {name: 'Alabama', pop: 4863300}
// {name: 'Alaska', pop: 741894},
// {name: 'Arizona', pop: 6931071},
// ...]
This would entail changes to the code above to work with the pop property of these objects, but it's probably more robust.
If your pop and state looks like:
var state = ['state1', 'state2', ...];
var pop = ['state1 pop', 'state2 pop', ...];
Then first of all, avg is already wrong. sum's value is running along with the loop turning avg's formula into sum as of iteration / array length instead of sum of all pops / array length. You should calculate the average beforehand. array.reduce will be your friend.
var average = pop.reduce(function(sum, val){return sum + val;}, 0) / pop.length;
Now for your filter operation, you can:
Zip up both arrays to one array using array.map.
Filter the resulting array with array.filter.
Finally, loop through the resulting array using array.forEach
Here's sample code:
var states = ['Alabama', 'Alaska'];
var pop = [4863300, 741894];
var average = pop.reduce(function(sum, val){return sum + val;}) / pop.length;
console.log('Average: ' + average);
states.map(function(state, index) {
// Convert 2 arrays to an array of objects representing state info
return { name: state, population: pop[index] };
}).filter(function(stateInfo) {
console.log(stateInfo);
// Filter each item by returning true on items you want to include
return stateInfo.population < average;
}).forEach(function(stateInfo) {
// Lastly, loop through your results
console.log(stateInfo.name + ' has ' + stateInfo.population + ' people');
});