Javascript - nested loops and indexes - javascript

I am trying to build an array that should look like this :
[
[{"name":"Mercury","index":0}],
[{"name":"Mercury","index":1},{"name":"Venus","index":1}],
[{"name":"Mercury","index":2},{"name":"Venus","index":2},{"name":"Earth","index":2}],
...
]
Each element is the concatenation of the previous and a new object, and all the indexes get updated to the latest value (e.g. Mercury's index is 0, then 1, etc.).
I have tried to build this array using the following code :
var b = [];
var buffer = [];
var names = ["Mercury","Venus","Earth"]
for (k=0;k<3;k++){
// This array is necessary because with real data there are multiple elements for each k
var a = [{"name":names[k],"index":0}];
buffer = buffer.concat(a);
// This is where the index of all the elements currently in the
// buffer (should) get(s) updated to the current k
for (n=0;n<buffer.length;n++){
buffer[n].index = k;
}
// Add the buffer to the final array
b.push(buffer);
}
console.log(b);
The final array (b) printed out to the console has the right number of objects in each element, but all the indexes everywhere are equal to the last value of k (2).
I don't understand why this is happening, and don't know how to fix it.


This is happening because every object in the inner array is actually the exact same object as the one stored in the previous outer array's entries - you're only storing references to the object, not copies. When you update the index in the object you're updating it everywhere.
To resolve this, you need to create new objects in each inner iteration, or use an object copying function such as ES6's Object.assign, jQuery's $.extend or Underscore's _.clone.
Here's a version that uses the first approach, and also uses two nested .map calls to produce both the inner (variable length) arrays and the outer array:
var names = ["Mercury","Venus","Earth"];
var b = names.map(function(_, index, a) {
return a.slice(0, index + 1).map(function(name) {
return {name: name, index: index};
});
});
or in ES6:
var names = ["Mercury","Venus","Earth"];
var b = names.map((_, index, a) => a.slice(0, index + 1).map(name => ({name, index})));


Try this:
var names = ["Mercury","Venus","Earth"];
var result = [];
for (var i=0; i<names.length; i++){
var _temp = [];
for(var j=0; j<=i; j++){
_temp.push({
name: names[j],
index:i
});
}
result.push(_temp);
}
console.log(result)


try this simple script:
var b = [];
var names = ["Mercury","Venus","Earth"];
for(var pos = 0; pos < names.length; pos++) {
var current = [];
for(var x = 0; x < pos+1; x++) {
current.push({"name": names[x], "index": pos});
}
b.push(current);
}

Related

How to create key value pair using two arrays in JavaScript?

I have two arrays, keys and commonkeys.
I want to create a key-value pair using these two arrays and the output should be like langKeys.
How to do that?
This is array one:
var keys=['en_US','es_ES', 'pt_PT','fr_FR','de_DE','ja_JP','it_IT']
This is array two:
var commonKeys=['en-*','es-*', 'pt-*','fr-*','de-*','ja-*','it-*', '*']
This is the output I need:
var langKeys = {
'en-*': 'en_US',
'es-*': 'es_ES',
'pt-*': 'pt_PT',
'fr-*': 'fr_FR',
'de-*': 'de_DE',
'ja-*': 'ja_JP',
'it-*': 'it_IT',
'*': 'en_US'
};

You can use map() function on one array and create your objects
var keys=['en_US','es_ES', 'pt_PT','fr_FR','de_DE','ja_JP','it_IT'];
var commonKeys=['en-*','es-*', 'pt-*','fr-*','de-*','ja-*','it-*', '*'];
var output = keys.map(function(obj,index){
var myobj = {};
myobj[commonKeys[index]] = obj;
return myobj;
});
console.log(output);

JavaScript is a very versatile language, so it is possible to do what you want in a number of ways. You could use a basic loop to iterate through the arrays, like this:
var keys=['en_US','es_ES', 'pt_PT','fr_FR','de_DE','ja_JP','it_IT']
var commonKeys=['en-*','es-*', 'pt-*','fr-*','de-*','ja-*','it-*', '*']
var i;
var currentKey;
var currentVal;
var result = {}
for (i = 0; i < keys.length; i++) {
currentKey = commonKeys[i];
currentVal = keys[i];
result[currentKey] = currentVal;
}
This example will work in all browsers.

ES6 update:
let commonKeys = ['en-*', 'es-*', 'pt-*', 'fr-*', 'de-*', 'ja-*', 'it-*', '*'];
let keys = ['en_US', 'es_ES', 'pt_PT', 'fr_FR', 'de_DE', 'ja_JP', 'it_IT', 'en_US'];
let zipArrays = (keysArray, valuesArray) => Object.fromEntries(keysArray.map((value, index) => [value, valuesArray[index]]));
let langKeys = zipArrays(commonKeys, keys);
console.log(langKeys);
// let langKeys = Object.fromEntries(commonKeys.map((val, ind) => [val, keys[ind]]));

What you want to achieve is to create an object from two arrays. The first array contains the values and the second array contains the properties names of the object.
As in javascript you can create new properties with variales, e.g.
objectName[expression] = value; // x = "age"; person[x] = 18,
you can simply do this:
var keys=['en_US','es_ES', 'pt_PT','fr_FR','de_DE','ja_JP','it_IT'];
var commonKeys=['en-*','es-*', 'pt-*','fr-*','de-*','ja-*','it-*', '*'];
var langKeys = {};
var i;
for (i=0; i < keys.length; i++) {
langKeys[commonKeys[i]] = keys[i];
}
EDIT
This will work only if both arrays have the same size (actually if keys is smaller or same size than commonKeys).
For the last element of langKeys in your example, you will have to add it manually after the loop.
What you wanted to achieve was maybe something more complicated, but then there is missing information in your question.

Try this may be it helps.
var langKeys = {};
var keys=['en_US','es_ES', 'pt_PT','fr_FR','de_DE','ja_JP','it_IT']
var commonKeys=['en-*','es-*', 'pt-*','fr-*','de-*','ja-*','it-*', '*']
function createArray(element, index, array) {
langKeys[element]= keys[index];
if(!keys[index]){
langKeys[element]= keys[index-(commonKeys.length-1)];
}
}
commonKeys.forEach(createArray);
console.info(langKeys);

Use a for loop to iterate through both of the arrays, and assign one to the other using array[i] where i is a variable representing the index position of the value.
var keys = ['en_US', 'es_ES', 'pt_PT', 'fr_FR', 'de_DE', 'ja_JP', 'it_IT'];
var commonKeys = ['en-*', 'es-*', 'pt-*', 'fr-*', 'de-*', 'ja-*', 'it-*', '*'];
var langKeys = {};
for (var i = 0; i < keys.length; i++) {
var commonkey = commonKeys[i];
langKeys[commonkey] = keys[i];
}
console.log(JSON.stringify(langKeys));

let keys = ['en_US', 'es_ES', 'pt_PT', 'fr_FR', 'de_DE', 'ja_JP', 'it_IT'];
let commonKeys = ['en-*', 'es-*', 'pt-*', 'fr-*', 'de-*', 'ja-*', 'it-*', '*'];
// declaration of empty object where we'll store the key:value
let result = {};
// iteration over first array to pick up the index number
for (let i in keys) {
// for educational purposes, showing the number stored in i (index)
console.log(`index number: ${i}`);
// filling the object with every element indicated by the index
// objects works in the basis of key:value so first position of the index(i)
// will be filled with the first position of the first array (keys) and the second array (commonKeys) and so on.
result[keys[i]] = commonKeys[i];
// keep in mind that for in will iterate through the whole array length
}
console.log(result);

How can I get a specific part of element in arrays

The title may a little confusing. But i think it is clear:
var a = ["A1", "B13", "C123"];
I want to ignore first value in elements and get rest of them. So my new array should look like this:
var b = ["1", "13", "123"];

Use .map() to create a new Array of modified values of the original.
var b = a.map(function(item) {
return item.slice(1);
});
This iterates the original Array, passes each item in the Array as the first argument to the function, and sets the return value of the function as the values for the new Array.
For IE8 and lower, you'll need to implement a patch. One is available from MDN.

Using .map, you can return a new array which is generated by passing every element in the existing array through a function:
var b = a.map(function(v) {
return v.substr(1);
});
Note that .map is an ES5 function that doesn't exist on older browsers. A shim is available at the above link.

var b = [];
for (var i = 0; i < a.length; ++i)
{
b[i] = a[i].substring(1);
}
Live Demo

The forEach way
var a = ["A1", "B13", "C123"],
b = [];
a.forEach(function (element) {
b.push(element.slice(1));
});
console.log(b);
on jsfiddle
The map way
var b = a.map(function (element) {
return element.slice(1);
});
The for way
var l = a.length;
var b = [];
for (var i = 0; i < l; i += 1) {
b.push(a[i].slice(1));
}
Ultimate speed is still the for loop (except for maybe grand daddy)
So as I ended up including all of the above, it didn't feel right to leave the grand daddy of them all out of the equation.
The while way
var b = [];
var i = 0;
var l = a.length;
while (i < l) {
b.push(a[i].slice(1));
i += 1;
}
I also include a RegExp and jquery version for a bit of a giggle.
(lodash also has it's own map function)
You can see the jsperf

javascript array with numeric index without undefineds

suppose I do..
var arr = Array();
var i = 3333;
arr[i] = "something";
if you do a stringify of this array it will return a string with a whole bunch of undefined numeric entries for those entries whose index is less than 3333...
is there a way to make javascript not do this?
I know that I can use an object {} but I would rather not since I want to do array operations such as shift() etc which are not available for objects

If you create an array per the OP, it only has one member with a property name of "333" and a length of 334 because length is always set to be at least one greater than the highest index. e.g.
var a = new Array(1000);
has a length of 1000 and no members,
var a = [];
var a[999] = 'foo';
has a length of 1000 and one member with a property name of "999".
The speedy way to only get defined members is to use for..in:
function myStringifyArray(a) {
var s = [];
var re = /^\d+$/;
for (var p in a) {
if (a.hasOwnProperty(p) && re.test(p)) {
s.push(a[p]);
}
}
return '' + s;
}
Note that the members may be returned out of order. If that is an issue, you can use a for loop instead, but it will be slower for very sparse arrays:
function myStringifyArray(a) {
var s = [];
var re = /^\d+$/;
for (var i=0, iLen=a.length; i<iLen; i++) {
if (a.hasOwnProperty(i)) {
s.push(a[i]);
}
}
return '' + s;
}
In some older browsers, iterating over the array actually created the missing members, but I don't think that's in issue in modern browsers.
Please test the above thoroughly.

The literal representation of an array has to have all the items of the array, otherwise the 3334th item would not end up at index 3333.
You can replace all undefined values in the array with something else that you want to use as empty items:
for (var i = 0; i < arr.length; i++) {
if (typeof arr[i] == 'undefined') arr[i] = '';
}
Another alternative would be to build your own stringify method, that would create assignments instead of an array literal. I.e. instead of a format like this:
[0,undefined,undefined,undefined,4,undefined,6,7,undefined,9]
your method would create something like:
(function(){
var result = [];
result[0] = 0;
result[4] = 4;
result[6] = 6;
result[7] = 7;
result[9] = 9;
return result;
}())
However, a format like that is of course not compatible with JSON, if that is what you need.

Creating dynamic objects to a parent object and assigning keys and values?

I am almost there with this but cannot seem to get this functionality going as planned.
I have two arrays: keyArray and ValArray;
What I am trying to do is to have a function pass two arguments (keyArr,valArr). Within this function, a parent object is declared and a (for-loop) loops through the passed argument's length (in this case "keyArr") creates new objects according the length of the passed argument. And then, the newly created objects are assigned the keys and values.
The issue is that I am able to create the parent object"mObj", and children Objects to "mObj", but am only able to assgin keys and values to the first child object "obj0" not rest of the children objects correctly. At the end of the code, this is what I would like to get:
enter code heremObj.obj0.firstname = John;
mObj.obj0.lastname = superfly;
mObj.obj0.email = "john.superfly#yahoo.com";
mObj.obj1.firstname = John;
mObj.obj1.lastname = superfly;
mObj.obj1.email = "john.superfly#yahoo.com";
mObj.obj2.firstname = John;
mObj.obj2.lastname = superfly;
mObj.obj2.email = "john.superfly#yahoo.com";
This is my code:
var keyArr = ["firstname","lastname","email"];
var valArr = ["John","Superfly","jsuperfly#yahoo.com"];
function test(keys,vals) // FUNCTION TEST ACCEPTS TWO ARGS
{
var mObj = {}; // PARENT OBJECT
var len = (keys.length); //ARGUMENT KEY'S LENGTH
for(var i=0; i<len; i++)
{
mObj["obj" + i] = {}; //CHILDREN OBJECTS ARE CREATED TO PARENT "mObj" OBJECT
mObj["obj" + i][keys[i]] = vals[i]; //KEYS AND VALUES ARE ASSIGNED HERE
}
alert(mObj.obj1.firstname); // CURRENTLY RETURNS "UNDEFINED"
}
test(keyArr,valArr);
Any insight into this would highly be appreciated.
Thank you.

Seems like this is what you need. This code will create as many child objects as the length of keyArr and valArr arrays. Although no idea why you would need it.
var keyArr = ["firstname", "lastname", "email"];
var valArr = ["John", "Superfly", "jsuperfly#yahoo.com"];
function test(keys, vals) {
var mObj = {},
i, j, len = keys.length;
for (i = 0; i < len; i++) {
mObj["obj" + i] = {};
for (j = 0; j < len; j++) {
mObj["obj" + i][keys[j]] = vals[j];
}
}
alert(mObj.obj1.firstname);
}
console.log( test(keyArr, valArr) );​

JavaScript: convert objects to array of objects

I have thousands of legacy code that stores array information in a non array.
For example:
container.object1 = someobject;
container.object2 = someotherobject;
container.object3 = anotherone;
What I want to have is:
container.objects[1], container.objects[2], container.objects[3] etc.
The 'object' part of the name is constant. The number part is the position it should be in the array.
How do I do this?

Assuming that object1, object2, etc... are sequential (like an array), then you can just iterate through the container object and find all the sequential objectN properties that exist and add them to an array and stop the loop when one is missing.
container.objects = []; // init empty array
var i = 1;
while (container["object" + i]) {
container.objects.push(container["object" + i]);
i++;
}
If you want the first item object1 to be in the [1] spot instead of the more typical [0] spot in the array, then you need to put an empty object into the array's zeroth slot to start with since your example doesn't have an object0 item.
container.objects = [{}]; // init array with first item empty as an empty object
var i = 1;
while (container["object" + i]) {
container.objects.push(container["object" + i]);
i++;
}

An alternate way to do this is by using keys.
var unsorted = objectwithobjects;
var keys = Object.keys(unsorted);
var items = [];
for (var j=0; j < keys.length; j++) {
items[j] = unsorted[keys[j]];
}
You can add an if-statement to check if a key contains 'object' and only add an element to your entry in that case (if 'objectwithobjects' contains other keys you don't want).

That is pretty easy:
var c = { objects: [] };
for (var o in container) {
var n = o.match(/^object(\d+)$/);
if (n) c.objects[n[1]] = container[o];
}
Now c is your new container object, where c.object[1] == container.object1

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