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How To Create Dynamic Arrays Varaibles in Javascript

Can you please let me know if it is possible to create dynamically sets of arrays in JS? I tried some thing like this but didn't work
for (i = 0; i < 3; i++) {
var item[i] = [];
}
item1.push(1);
console.log(item1);
<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.0/jquery.min.js"></script>

You're almost there. Assuming you're trying to create a two dimensional array (an array of arrays), you just have to declare the top level array and then reference the first level array with [x] array syntax like this:
var items = [];
for (i = 0; i < 3; i++) {
items[i] = [];
}
// Here items is an array of arrays where each first level array entry
// is an empty array. You can then put things into those empty arrays
// You can reference the first level array here
items[1].push(1);
items[1].push(2);
console.log(items[1]); // [1,2]

Find duplicate object values in an array and merge them - JAVASCRIPT

I have an array of objects which contain certain duplicate properties: Following is the array sample:
var jsonData = [{x:12, machine1: 7}, {x:15, machine2:7},{x:12, machine2: 8}];
So what i need is to merge the objects with same values of x like the following array:
var jsonData = [{x:12, machine1:7, machine2:8}, {x:15, machine2:7}]

I like the lodash library.
https://lodash.com/docs#groupBy
_.groupBy(jsonData, 'x') produces:
12: [ {x=12, machine1=7}, {x=12, machine2=8} ],
15: [ {x=15, machine2=7} ]
your desired result is achieved like this:
var jsonData = [{x:12, machine1: 7}, {x:15, machine2:7},{x:12, machine2: 8}];
var groupedByX = _.groupBy(jsonData, 'x');
var result = [];
_.forEach(groupedByX, function(value, key){
var obj = {};
for(var i=0; i<value.length; i++) {
_.defaults(obj, value[i]);
}
result.push(obj);
});

I'm not sure if you're looking for pure JavaScript, but if you are, here's one solution. It's a bit heavy on nesting, but it gets the job done.
// Loop through all objects in the array
for (var i = 0; i < jsonData.length; i++) {
// Loop through all of the objects beyond i
// Don't increment automatically; we will do this later
for (var j = i+1; j < jsonData.length; ) {
// Check if our x values are a match
if (jsonData[i].x == jsonData[j].x) {
// Loop through all of the keys in our matching object
for (var key in jsonData[j]) {
// Ensure the key actually belongs to the object
// This is to avoid any prototype inheritance problems
if (jsonData[j].hasOwnProperty(key)) {
// Copy over the values to the first object
// Note this will overwrite any values if the key already exists!
jsonData[i][key] = jsonData[j][key];
}
}
// After copying the matching object, delete it from the array
// By deleting this object, the "next" object in the array moves back one
// Therefore it will be what j is prior to being incremented
// This is why we don't automatically increment
jsonData.splice(j, 1);
} else {
// If there's no match, increment to the next object to check
j++;
}
}
}
Note there is no defensive code in this sample; you probably want to add a few checks to make sure the data you have is formatted correctly before passing it along.
Also keep in mind that you might have to decide how to handle instances where two keys overlap but do not match (e.g. two objects both having machine1, but one with the value of 5 and the other with the value of 9). As is, whatever object comes later in the array will take precedence.

const mergeUnique = (list, $M = new Map(), id) => {
list.map(e => $M.has(e[id]) ? $M.set(e[id], { ...e, ...$M.get(e[id]) }) : $M.set(e[id], e));
return Array.from($M.values());
};
id would be x in your case
i created a jsperf with email as identifier: https://jsperf.com/mergeobjectswithmap/
it's a lot faster :)

creating multi-dim arrays (JS)

I was trying to create a 3-dimensional array and couldn't find an easy way to do it.
array = [[[]]];
or
array = [][][];
or
array = []; array[] = []; array[][] = [];
would for example not work. (the console'd say the second array is 'undefined' and not an object, or for the second and third example give a parse error).
I cannot hard-code the information either, as I have no idea what the indexes and contents of the array are going to be (they are created 'on the fly' and depending on the input of a user. eg the first array might have the index 4192). I may have to create every array before assigning them, but it would be so much easier and faster if there's an easier way to define 3-dimensional arrays. (there'll be about 2 arrays, 25 subarrays and 800 subsubarrays total) every millisecond saves a life, so to say.
help please?

JavaScript is dynamically typed. Just store arrays in an array.
function loadRow() {
return [1, 2, 3];
}
var array = [];
array.push(loadRow());
array.push(loadRow());
console.log(array[1][2]); // prints 3

Since arrays in javascript aren't true arrays, there isn't really a multidimensional array. In javascript, you just have an arrays within an array. You can define the array statically like this:
var a = [
[1,2,3],
[4,5,6],
[7,8,9]
];
Or dynamically like this:
var d = [];
var d_length = 10;
for (var i = 0;i<d_length;i++) {
d[i] = [];
}
UPDATE
You could also use some helper functions:
function ensureDimensions(arr,i,j,k) {
if(!arr[i]) {
arr[i] = [];
}
if(!arr[i][j]) {
arr[i][j] = [];
}
}
function getValue(arr,i,j,k) {
ensureDimensions(i,j,k);
return arr[i][j][k];
}
function setValue(arr,newVal,i,j,k) {
ensureDimensions(i,j,k);
arr[i][j][k] = newVal;
}

Sort a three dimensional array in Javascript

Consider this Array
var LIST =[];
LIST['C']=[];
LIST['B']=[];
LIST['C']['cc']=[];
LIST['B']['bb']=[];
LIST['C']['cc'].push('cc0');
LIST['C']['cc'].push('cc1');
LIST['C']['cc'].push('cc2');
LIST['B']['bb'].push('bb0');
LIST['B']['bb'].push('bb1');
LIST['B']['bb'].push('bb2');
I can loop through this array like
for(var i in LIST){
console.log(i)//C,B
var level1=LIST[i];
for(var j in level1){
console.log(j)//cc,bb
// etc...
}
}
Fine.. I have few basic questions.
1.How to sort the array in each level?
One level can be sort by .sort(fn) method . How can i pass to inner levels?
2.Why the indexOf method does not works to find the elements in first two levels?
If it's because of the a non string parameter .. how can i search an array items in array if the item is not string?
3.How for(var i in LIST) works ?
I just need a basic understanding of indexing and looping through array ..
Thanks ..

LIST is NOT a three dimensional array in Javascript, it is just an array.
//declare an array which names LIST.
var LIST = [];
//set a property named 'C' of the LIST to be an array.
LIST['C']=[];
//set a property named 'B' of the LIST to be an array.
LIST['B']=[];
//set a property named 'cc' of the 'LIST.C'(which is an array object)
LIST['C']['cc']=[];
//set a property named 'bb' of the 'LIST.B'(which is an array object)
LIST['B']['bb']=[];
The fact is you only need to let the last level to be an array, see my example code below.
function iterateOrderd(obj) {
if (obj instanceof Array) {
obj.sort();
for (var j = 0, l=obj.length; j < l; j++) {
console.log(obj[j]);
}
} else {
var sortable = [];
for (var i in obj) {
if (obj.hasOwnProperty(i)) {
sortable.push(i);
}
}
sortable.sort();
for (var j = 0, l=sortable.length; j < l; j++) {
console.log(sortable[j]);
iterateOrderd(obj[sortable[j]]);
}
}
}
var LIST = {};
LIST['C'] = {};
LIST['B'] = {};
LIST['C']['cc']=[];
LIST['B']['bb']=[];
LIST['C']['cc'].push('cc0');
LIST['C']['cc'].push('cc1');
LIST['C']['cc'].push('cc2');
LIST['B']['bb'].push('bb0');
LIST['B']['bb'].push('bb1');
LIST['B']['bb'].push('bb2');
iterateOrderd(LIST);

You need to know that Array inherits from Object.
In JavaScript, any Object instance is an associative array(!), so acts like an Array in PHP. For example:
var o = {}; // or new Object();
o['foo'] = 'bar';
o[0] = 'baz';
for (i in o) { console.log(i, o[i]); }
Sorting an Object does not make much sense. indexOf would kinda work in theory, but is not implemented.
Arrays are ordered lists. Array instances have push(), length, indexOf(), sort() etc., but those only work for numerical indexes. But again, Array inherits from Object, so any array can also contain non-numerical index entries:
var a = []; // or new Array();
a[0] = 'foo'; // a.length is now 1
a.push('baz'); // a[1] === 'baz'
a.qux = 1; // will not affect a.length
a.sort(); // will not affect a.qux
for (i in a) { console.log(i, a[i]); }
I recommend playing around with arrays and objects, and you'll soon get the point.

What is your sorting criteria ? I mean how will you say array firstArray comes before secondArray?
regarding the for (counter in myArray), counter will take values of an array element in every iteration.
for (counter in [0,1,5]), counter will have values 0, 1 and 5 in the 3 iterations.
In your case, i will have values LIST['B'] and LIST['C'] in the two iterations and j will have values LIST['B']['bb'], LIST['B']['cc'], LIST['C']['bb'] and LIST['C']['cc'].
Both i and j will be arrays.

Group javascript items by one property

My question is related to this question. You will have to first read it.
var ids = "1*2*3";
var Name ="John*Brain*Andy";
var Code ="A12*B22*B22";
Now that I have an array of javascript objects. I want to group my objects based on CODE. So there can be duplicate codes in that code string.
As per the above changed strings, I have same code for Brain and Andy. So, now I want two arrays. In one there will be only one object containing details of only John and in the other object there will be two objects containing details of Brain and Andy.
Just for example I've taken 3 items. In actual there can be many and also there can be many set of distinct codes.
UPDATE
I needed the structure like the one built in groupMap object by the #Pointy. But I will use #patrick's code to achieve that structure. Many thanks to both of them.

It is a little hard to tell the exact resulting structure that you want.
This code:
// Split values into arrays
Code = Code.split('*');
Name = Name.split('*');
ids = ids.split('*');
// cache the length of one and create the result object
var length = Code.length;
var result = {};
// Iterate over each array item
// If we come across a new code,
// add it to result with an empty array
for(var i = 0; i < length; i++) {
if(Code[i] in result == false) {
result[ Code[i] ] = [];
}
// Push a new object into the Code at "i" with the Name and ID at "i"
result[ Code[i] ].push({ name:Name[i], id:ids[i] });
}
Will produce this structure:
// Resulting object
{
// A12 has array with one object
A12: [ {id: "1", name: "John"} ],
// B22 has array with two objects
B22: [ {id: "2", name: "Brain"},
{id: "3", name: "Andy"}
]
}

Split the strings on "*" so that you have 3 arrays.
Build objects from like-indexed elements of each array.
While building those objects, collect a second object that contains arrays for each "Code" value.
Code:
function toGroups(ids, names, codes) {
ids = ids.split('*');
names = names.split('*');
codes = codes.split('*');
if (ids.length !== names.length || ids.length !== codes.length)
throw "Invalid strings";
var objects = [], groupMap = {};
for (var i = 0; i < ids.length; ++i) {
var o = { id: ids[i], name: names[i], code: code[i] };
objects.push(o);
if (groupMap[o.code]) {
groupMap[o.code].push(o);
else
groupMap[o.code] = [o];
}
return { objects: objects, groupMap: groupMap };
}
The "two arrays" you say you want will be in the "groupMap" property of the object returned by that function.