Develop Reference

Get "leaderboard" of list of numbers

I am trying to get a kind of "leaderboard" from a list of numbers. I was thinking of making an array with all the numbers like this
var array = [];
for (a = 0; a < Object.keys(wallets.data).length; a++) { //var wallets = a JSON (parsed) response code from an API.
if (wallets.data[a].balance.amount > 0) {
array.push(wallets.data[a].balance.amount)
}
}
//Add some magic code here that sorts the array into descending numbers
This is a great option, however I need some other values to come with the numbers (one string). That's why I figured JSON would be a better option than an array.
I just have no idea how I would implement this.
I would like to get a json like this:
[
[
"ETH":
{
"balance":315
}
],
[
"BTC":
{
"balance":654
}
],
[
"LTC":
{
"balance":20
}
]
]
And then afterwards being able to call them sorted descending by balance something like this:
var jsonarray[0].balance = Highest number (654)
var jsonarray[1].balance = Second highest number (315)
var jsonarray[2].balance = Third highest number (20)
If any of you could help me out or point me in the right direction I would appreciate it greatly.
PS: I need this to happen in RAW JS without any html or libraries.

You should sort the objects before making them a JSON. You can write your own function or use a lambda. See this [https://stackoverflow.com/questions/1129216/sort-array-of-objects-by-string-property-value]

Since you are dealing with cryptocurrency you can use the currency-code as a unique identifier.
Instead of an array, you can define an object with the currency as properties like this:
const coins = {
ETH: [300, 200, 500],
BTC: [20000, 15000, 17000]
}
then you can access each one and use Math.max or Math.min to grab the highest / lowest value of that hashmap. E.G. Math.max(coins.BTC)
And if you need to iterate over the coins you have Object.keys:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Object/keys

Thank you all for your answer. I ended up using something like:
leaderboard = []
for (a = 0; a < Object.keys(wallets.data).length; a++) {
if (wallets.data[a].balance.amount > 0) {
leaderboard.push({"currency":wallets.data[a].balance.currency, "price":accprice}) //accprice = variable which contains the value of the userhold coins of the current coin in EUR
}
}
console.log(leaderboard.sort(sort_by('price', true, parseInt)));

Pass arbitrary Javascript data object to Node.js C++ addon

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.

How to convert arrays to objects in javascript?

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

How to find the position of all array items from a loop

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');
});

Accessing a javascript object in D3.js

A javascript data object (JSON notation) has been created with the following content:
"[
{"range":"Shape","values":[{"idx":0,"val":"Random"},{"idx":1,"val":"Line"},{"idx":2,"val":"Square"},{"idx":3,"val":"Circle"},{"idx":4,"val":"Oval"},{"idx":5,"val":"Egg"}]},
{"range":"Color","values":[{"idx":0,"val":"Red"},{"idx":1,"val":"Blue"},{"idx":2,"val":"Yellow"},{"idx":3,"val":"Green"},{"idx":4,"val":"Cyan"}]}
]"
In a next step the index of an ordinal value has to be found in this object. The function should find the index of the value 'Blue' in the range 'Color'.
So the function should have the meta scripting form
f("Color")("Blue")=1
What is the most elegant form to create such a function in the context of D3 and javascript?

Depending on your use case, it might make sense to convert the data structure to a different structure more suitable for direct access. E.g. you could convert your structure to
var data = {
Shape: ['Random', 'Line', ...],
// ...
};
and access it with
data['Shape'].indexOf('Line') // or data.Shape.indexOf('Line')
Or go even one step further and convert to
var data = {
Shape: {
Random: 0,
Line: 1,
// ...
},
// ...
};
and access it with
data['Shape']['Line'] // or data.Shape.Line
What the best solution is depends on the actual use case.
Converting the structure dynamically is pretty straight forward. Here is an example to convert it to the first suggestion:
var newData = {};
data.forEach(function(item) {
newData[item.range] =
item.values.map(function(value) { return value.val; });
});
This would also reduce redundancy (e.g. idx seems to correspond with the element index).

Would this work for you ?
var dataJson = '[ \
{"range":"Shape","values":[{"idx":0,"val":"Random"},{"idx":1,"val":"Line"},{"idx":2,"val":"Square"},{"idx":3,"val":"Circle"},{"idx":4,"val":"Oval"},{"idx":5,"val":"Egg"}]},\
{"range":"Color","values":[{"idx":0,"val":"Red"},{"idx":1,"val":"Blue"},{"idx":2,"val":"Yellow"},{"idx":3,"val":"Green"},{"idx":4,"val":"Cyan"}]}\
]';
var data = JSON.parse(dataJson);
for (each in data){
if ( (data[each].range) === 'Color'){
for (eachVal in data[each].values){
if (data[each].values[eachVal].val === 'Blue'){
alert(data[each].values[eachVal].idx);
}
}
} ;
}
And here is the JSFiddle for you too.