Develop Reference

Creating new array from unique elements found in array

I was given an assignment:
Finding unique elements in an array and creating a new array from these unique elements.
The professor gave us the pseudocode to code this assignment - it should be straightforward but my code is not working.
Here is my attempt:
// search for unique birthdays in the array
function find(birthdays) {
var uniqueBirthdays = [];
for (var i = 1; i <= birthdays.length; i = i + 2) {
var count = 0;
for (var j = 1; j <= birthdays.length; j = j + 2) {
if (birthdays[i] == birthdays[j]) {
count++;
}
}
if (count == 1) {
var n = uniqueBirthdays.length;
uniqueBirthdays[n] = birthdays[i - 1];
}
}
return uniqueBirthdays;
}
I have tried checking for indentation errors as well as a number of other things but can not figure out why as the array is traversed it is giving each element a count of only 1 (meaning there are no matching elements) - it does not seem to be traversing the array more than once so no elements have a count greater than 1 - even though I am using nested for loops.
I have increased the intervals by 2 because I need to compare every other element - there is a number assigned to each birthday so the array may look like:
['0001'][12/15]['0002'[03/12]...
I am brand new so I may be overlooking simple but ive tried so many things and i can not understand why this code isnt working - it is returning back all of the elements that are assigned to the birthdays instead of just the unique ones.
Any help that will point me in the right direction is very much appreciated.

You were very close, and there were just a couple mistakes. The only things that did not work were the way you wrote your for loops:
for (var i = 1; i <= birthdays.length; i = i + 2) {
Array indexes start at 0, so if you want to process the first element, use var i = 0;
Since these indexes start at 0, for an Array of 3 elements, the last index is 2. So you only want to run your loop while i is less than the array length: i < birthdays.length
You were skipping elements by doing i = i + 2. There seems to be no reason for it?
Something else worth mentionning: in JS, indentation does not matter - well, it does, but only to avoid making your eyes bleed. In fact, most websites use minified versions of their code, which fits on a single (often very long and ugly) line (example).
Here is your code, with only two lines fixed:
function find(birthdays) {
var uniqueBirthdays = [];
for (var i = 0; i < birthdays.length; i = i + 1) { // <-----
var count = 0;
for (var j = 0; j < birthdays.length; j = j + 1) { // <-----
if (birthdays[i] == birthdays[j]) {
count++;
}
}
if (count == 1) {
var n = uniqueBirthdays.length;
uniqueBirthdays[n] = birthdays[i];
}
}
return uniqueBirthdays;
}
// I used letters instead of birthdays for easier demo checking
var birthdays = ['a', 'b', 'a', 'c'];
console.log( find(birthdays) ); // ["b", "c"]

JS have direct methods tor that use Array.indexOf(), Array.lastIndexOf() and Array.filter()
uniques elements have same first position and last position
sample code:
const initailArray = [...'ldfkjlqklnmbnmykdshgmkudqjshmjfhmsdjhmjh']
const uniqueLetters = initailArray.filter((c,i,a)=>a.indexOf(c)===a.lastIndexOf(c)).sort()
console.log(JSON.stringify(uniqueLetters))

multidimensional array indexOf not working js

I'm trying to find an index of a number in a 2d array, but console gives out
Uncaught TypeError: block[((a * 10) + c)].indexOf is not a function
I think it has something to do with the way of accessing the array element, but can't seem to find the problem.
Here's the code.
var block = [];
var temp;
var del;
for(var a = 0;a < 9;a++){
for(var b = 0;b < 9;b++){
temp = parseInt(prompt("enter element number " + b + " of row number " + a));
console.log(temp);
if(temp>0){
block[a*10+b] = temp;
}else{
block[a*10+b] = [1,2,3,4,5,6,7,8,9];
}
// console.log(block[a*10+b]);
}
}
for(var a = 0;a < 9;a++){
for(var b = 0;b < 9;b++){
if(typeof(block[a][b]) == "number"){
for(var c = 0;c < 9;c++){
if(c != b){
del = block[a*10+c].indexOf(b);
block[a*10+c].splice(del,1);
}
}
}
}
}

You have a mix of data types assigned to the block array. When the user enters a value that is not numeric, you assign indeed a nested array to one of the block elements, but not so when the user enters a valid number.
From what I think you are doing (a Sudoko game?) this might be intended: the numbers are known values in the grid, the nested arrays represent a list of values that are still possible at that particular cell.
But then in the second part of your code, you should check in which of the two cases you are, as you only want to remove array elements if the value you are looking at is indeed an array. This test you can do with Array.isArray().
There are also some other issues in the second part of your script:
The expression block[a][b] is not consistent with how you have filled that array: it should be block[a*10+b] to be consistent.
the b in .indexOf(b) is wrong: you are not looking for that value, but for block[a*10+b].
the splice() is always executed, even if the indexOf returned -1. This leads to an undesired effect, because if the first argument to splice() is negative, the index really is counted from the end of the array, and still an element is removed from the array. This should not happen: you should only execute the splice if the indexOf result is non-negative.
Below I have put a working version, but in order to avoid the almost endless prompts, I have provided this snippet with a textarea where you can input the complete 9x9 grid in one go, and then press a button to start the execution of your code:
document.querySelector('button').onclick = function () {
var block = [];
var temp;
var del;
var text = document.querySelector('textarea').value.replace(/\s+/g, '');
for(var a = 0;a < 9;a++){
for(var b = 0;b < 9;b++){
temp = parseInt(text[a*9+b]); // <-- get char from text area
if(temp>0){
block[a*10+b] = temp;
}else{
block[a*10+b] = [1,2,3,4,5,6,7,8,9];
}
}
}
for(var a = 0;a < 9;a++){
for(var b = 0;b < 9;b++){
var num = block[a*10+b]; // <-- get content, fix the index issue
if(typeof num == "number"){
for(var c = 0;c < 9;c++){
if(c != b && Array.isArray(block[a*10+c])){ //<-- add array-test
del = block[a*10+c].indexOf(num); // <-- not b, but num
if (del > -1) // <-- only splice when found
block[a*10+c].splice(del,1);
}
}
}
}
}
document.querySelector('pre').textContent = 'block='+ JSON.stringify(block);
};
<textarea rows=9>
53..7....
6..195...
.98....6.
8...6...3
4..8.3..1
7...2...6
.6....28.
...419..5
....8..79
</textarea>
<button>Process</button>
<pre></pre>
Note that there are elements in block which remain null. I suppose you intended this: as you multiply a with 10, and only store 9 values per "row", there is always one index that remains untouched.

I haven't looked over your second for loop, but you can try applying similar logic there as in the snippet I've provided. The issue is that you need to create a temporary array inside the outer for loop over values of a (but NOT inside the inner, nested for loop over values of b). Inside the for loop for values of b, then, you need to push something into that temporary array (which I called temp). Then, outside of the b for loop, but before the next iteration of a, push that temporary array temp to the block array. In this way, you will generate a 2D array.
var block = [];
var del;
for(var a = 0; a < 9; a++) {
let temp = [];
for(var b = 0; b < 9; b++) {
let num = parseInt(prompt(`Enter element ${b} of row ${a}:`));
if (num > 0) {
temp.push(num);
} else {
// block[a*10+b] = [1,2,3,4,5,6,7,8,9];
temp.push(b);
}
}
block.push(temp);
}

how to optimize code in javascript

I think the code(below) is optimized (just use less variables than my initial version of the same logic).
How do I really know if its properly optimized ?
What factors should I consider during optimization ?
Here is the code (
also on jsfiddle )
function process(arr){
var processed = [];
for(var i=0,len=arr.length;i<len;i++){
if(processed.indexOf(arr[i]) < 0){
var nodes = findIndexes(arr,arr[i]);
if(nodes.length > 1){
for(var j=0,jlen=nodes.length;j<jlen;j++){
arr[nodes[j]] = arr[nodes[j]] + '(' + ( j + 1 ) + ')';
}
}
processed.push(arr[i]);
}
}
return arr;
}
function findIndexes(arr,val){
var node = [];
for(var i=0,len=arr.length;i<len;i++){
if(arr[i] === val){
node.push(i);
}
}
return node;
}
// input
var arr = ['aa','bb','bb','aa','cc','dd','cc','ff']
console.log(process(arr));
//output: ["aa(1)", "bb(1)", "bb(2)", "aa(2)", "cc(1)", "dd", "cc(2)", "ff"]
Here is the explanation of the code. 'process' function looks for the same values inside array and for every same values it changes the value by post pending a number to that values, "number" indicates the count of the value as it found in array.
for example
arr = ["x","x","y","z"] will return ["x(1)","x(2)","y","z"]
"y" and "z" are unchanged because they appeared only once.
To optimize I have used an array named as processed that is used to hold values that are just processed inside main for loop, so in next iterations it can be determined that the new iteration value is already processed or not by checking through the array.indexOf method, if the value is already processed then it can safely skip the underlying logic (if/for statements).
Now I have no idea how to further optimize it other than changing the whole process logic.

Optimizations in a broad sense will involve simplifying code, precomputing results which are repeatedly reused, and organizing code so more results can be reused.
Your fiddle code produced following result on analysis.
Logical LOC: 26
Mean parameter count: 3
Cyclomatic complexity: 7
Cyclomatic complexity density: 27%
Maintainability index: 104
Lines of Code (LOC)– Indicates the approximate number of lines in the code. The count is based on the IL code and is therefore not the exact number of lines in the source code file. A very high count might indicate that a type or method is trying to do too much work and should be split up. It might also indicate that the type or method might be hard to maintain.
Maintainability Index – Calculates an index value between 0 and 100 that represents the relative ease of maintaining the code. A high value means better maintainability. Color coded ratings can be used to quickly identify trouble spots in your code. A green rating is between 20 and 100 and indicates that the code has good maintainability. A yellow rating is between 10 and 19 and indicates that the code is moderately maintainable. A red rating is a rating between 0 and 9 and indicates low maintainability.
Cyclomatic Complexity – Measures the structural complexity of the code. It is created by calculating the number of different code paths in the flow of the program. A program that has complex control flow will require more tests to achieve good code coverage and will be less maintainable.
Check code complexities using online tool for your javascript code.
Reference : Link1,Link 2
Javascript optimiser page
Reference(Provides you with different techniques that you should keep in mind while optimising)

You can do it in a single loop:
function process2(arr) {
var out = arr.slice(0),
seen = {},
len = arr.length,
i, key, item, count;
for (i = 0; i < len; ++i) {
key = out[i];
item = seen[key];
if (!item) {
// firstIndex, count
seen[key] = item = [i, 0];
}
count = ++item[1];
if (count > 1) {
if (count === 2) {
out[item[0]] = key + '(1)';
}
out[i] = key + '(' + count + ')';
}
}
return out;
}
// input
var arr = ['aa', 'bb', 'bb', 'aa', 'cc', 'dd', 'cc', 'ff']
console.time('p2');
console.log(process2(arr));
console.timeEnd('p2');
From benchmarking, process2 is approximately 2x faster than process1. That's just a really naive first pass at the problem.

And yet another way to optimize your code with less changes:
In your specific case you go through the whole array for each new found entry although all previous entries have already been processed so it should be possible to opimize further by passing the current index to findIndexes:
function findIndexes(arr,val, fromIndex){
var node = [];
for(var i=fromIndex,len=arr.length;i<len;i++){
if(arr[i] === val){
node.push(i);
}
}
return node;
}

Currrently your code has a O(n^2) complextity. This is caused by your outer loop of arr in process then a call to findIndexes which again loops through arr.
You can simplify this to an O(n) algorithm that loops through the array twice:
function process(arr) {
var result = [];
var counter = {}, counts = {};
var len = arr.length;
for(var i = 0; i < len; i++){
var value = arr[i];
counter[value] = 1;
counts[value] = (counts[value] || 0) + 1;
}
for(var i = 0; i < len; i++){
var value = arr[i];
if(counts[value] == 1) {
result.push(value);
} else {
result.push(value + "(" + counter[value]++ + ")");
}
}
return result;
}

Here's an example that doesn't use nested loops, and uses an object to store key information:
var obj = {};
// loop over the array storing the elements as keys in the object
// if a duplicate element is found, increment the count value
for (var i = 0, l = arr.length; i < l; i++) {
var key = arr[i];
if (!obj[key]) obj[key] = { count: 0, level: 0 };
obj[key].count++;
}
// remove all the key/values where the count is 1
// ie there are no duplicates
for (var p in obj) {
if (obj[p].count === 1) delete obj[p];
}
// for each element in the original array, increase its 'level'
// amend the element with the count
// reduce the count
for (var i = 0, l = arr.length; i < l; i++) {
var key = arr[i];
if (obj[key] && obj[key].count > 0) {
obj[key].level++;
arr[i] = key + '(' + obj[key].level + ')';
obj[key].count--;
}
}
DEMO

How to check for specific string in a dictionary?

I have a dictionary like:
a = {"staticData":['----','Blue','Green'], "inData":['Indatahere','----','----']}
How can I find that if the dictionary contains "----", in any of the key's values.
Any Javascript function?
EDIT:
What if the case is like this?
a = {"staticData":[], "inData":['Indatahere','----','----']}
It's giving this Error:
TypeError: a[elem].indexOf is not a function

Here is the code:
var a = {"staticData":['----','Blue','Green'], "inData":['Indatahere','----','----']};
for(var key in a){
var value = a[key];
for(var i=0; i<value.length; i++){
if(value[i] == '----') alert("Found '----' in '" + key + "' at index " + i);
};
}
EDIT: Changed iteration over array to normal way after comment.

Use indexOf to search each array in the a object:
for (elem in a)
{
if (a[elem].indexOf("----") != -1)
alert('---- found at ' + a[elem]);
}
EDIT
For this error: TypeError: a[elem].indexOf is not a function the browser possibly considers an empty element to be a non-string type; non-string type does not have an indexOf method.
This code checks the length of the array element (if the element is empty before interpreting the indexOf function.
for (elem in a)
{
if (a[elem].length > 0 && a[elem].indexOf("----") != -1)
alert('---- found at ' + a[elem]);
}
If you wish to support IE < 9, see this post to conditionally add a indexOf definition to the Array object. The post also mentions a Jquery alternative.
The SO post mentioned above lists this Mozilla version of indexOf function.
if (!Array.prototype.indexOf)
{
Array.prototype.indexOf = function(elt /*, from*/)
{
var len = this.length >>> 0;
var from = Number(arguments[1]) || 0;
from = (from < 0)
? Math.ceil(from)
: Math.floor(from);
if (from < 0)
from += len;
for (; from < len; from++)
{
if (from in this &&
this[from] === elt)
return from;
}
return -1;
};
}

If you know exactly the nesting level of your value, then a quick solution (as suggested in other answers) is possible.
However, if you need a deep traversal search, you're gonna need a recursive version of the solutions, something like:
function FindTraverse(data, match)
{
for (var prop in data)
{
if (!data.hasOwnProperty(prop)) continue;
if (data[prop] == match) return true;
if (typeof data[prop] == 'object' && FindTraverse(data[prop], match)) return true;
}
return false;
}
Examples:
FindTraverse({a:'Foo',b:'Bar'}, 'Bar') // true
FindTraverse(['Foo','Bar'], 'Bar') // true
FindTraverse([{name:'Foo'},{name:'Bar'}], 'Bar') // true
FindTraverse({a:{name:'FooBar'},b:'Bar'}, 'FooBar') // true
However, if you're looking for a more thorough solution, use a framework like jsTraverse

Use Object.getOwnPropertyNames().
You have to write two nested loops. With Object.getOwnPropertyNames you are accessing an array which consists of property names of an object. You will then need to loop over the value of those properties and identify the correct element within this second array.
a = {"staticData":['----','Blue','Green'], "inData":['Indatahere','----','----']}
props = Object.getOwnPropertyNames(a);
for (i=0;i < props.length;i ++) {
for (z = 0; z < a[props[i]].length; z ++) {
//console.log(a[props[i]][z])
if ( (a[props[i]][z]) == '----') {
console.log("I have found an item with ----")
};
}
}

JavaScript Associate Array access returns "literal" Array Prototype Code

Here is my code so far for my school project (using Murach's JavaScript and DOM Scripting by Ray Harris). The chapter is only about Arrays and does not cover Prototypes, but I wanted to try it out based on Internet tutorials and references:
/*
Operation
This application stores the last name, first name, and score for
one or more students and it calculates the average score for all of the scores
that have been entered. When the user clicks on the Clear button, this
application clears the score data from this application. When the user clicks
on the Sort button, this application sorts the data in alphabetical order by
last name.
Specifications
The program should use one or more arrays to store the data.
Assume that the user will enter valid data.
*/
var $ = function (id)
{
return document.getElementById(id);
}
/*
Array prototype object extension for averaging the contents
"Adding a method to the built-in Array object to extract the average
of any numerical values stored in the array is therefore a useful
addition to that object." http://javascript.about.com/library/blaravg.htm
*/
Array.prototype.average = function ()
{
var avg = 0;
var count = 0;
for (var i = 0; i<this.length; i++)
{
//never gets here:
alert(i + ": " + this[i]);
var e = +this[i];
if(!e && this[i] !== 0 && this[i] !== '0')
{
e--;
}
if (this[i] == e)
{
avg += e;
count++;
}
}
return avg / count;
}
var addScore = function ()
{
studentScores[$('last_name').value + ', ' + $('first_name').value] = $('score').value;
update();
}
var clearScore = function ()
{
for (var i in studentScores)
{
studentScores[i] = '';
}
update();
}
var sortScore = function ()
{
scores.sort();
update();
}
var update = function ()
{
var result = '';
for (var i in studentScores)
{
result += (i + ': ' + studentScores[i] + '\n');
}
$('scores').value = result;
$('average_score').value = studentScores.average().toFixed(1);
}
window.onload = function ()
{
//a variable is initialized inside a function without var, it will have a global scope:
studentScores = [];
$('add_button').onclick = addScore;
$('sort_button').onclick = sortScore;
$('clear_button').onclick = clearScore;
$('last_name').focus();
}
When the code enters the "update()" function (end of the "addScore()" function) and accesses the array,
it populates the "literal" code from the Prototype into the text area (and fails to find the average on the next line):
I don't have enough rep points to post the image, but here is my output (there are no errors in the Chrome JS Console):
lowe, doug: 82
average: function ()
{
var avg = 0;
var count = 0;
for (var i = 0; i<this.length; i++)
{
//never gets here:
alert(i + ": " + this[i]);
var e = +this[i];
if(!e && this[i] !== 0 && this[i] !== '0')
{
e--;
}
if (this[i] == e)
{
avg += e;
count++;
}
}
return avg / count;
}
Any help appreciated (best practice or algorithm suggestions welcome)

Change this:
studentScores = []
to this:
studentScores = {}
...so that you're using an Object instead of an Array.
Your for loop in average() is just iterating numeric indices instead of the non-numeric keys you created.
Create your average() method as a standalone function like the others, and pass studentScores to it to calculate the average, and then use for-in instead of for.

That's simple: Do not use for…in enumerations for looping Arrays! You do so in your clearScore and update functions.
for (var prop in obj) loops over all [enumerable] properties, including those that are inherited from Array.prototype (for Array objects at least). A for (var i=0; i<array.length; i++) loop will not have that problem.

You have to decide whether studentScores is intended to be an array (i.e., an integer is used to access the stored data) or an Object/Associative Array (a string is used to set/get an element).
If you want to use the student's name as the key, you should declare studentScores as an object, and your 'average' method would have to be added to the Object prototype (which I don't recommend).
With the current state of the code, you have stumbled on the fact that an Array is also an object, and can have arbitrary properties attached to it, like any other object. You have added properties by name, but in your average method, you are trying to access numerically based indices. But that's not where the data you're adding is stored.
> a = [];
[]
> a['foo'] = 'bar';
'bar'
> a.length
0
> a[3] = 0;
0
> a.length
4