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Algorithm to sort an array in JS

I have an array
var arr= [
["PROPRI","PORVEC"],
["AJATRN","PROPRI"],
["BASMON","CALVI"],
["GHICIA","FOLELI"],
["FOLELI","BASMON"],
["PORVEC","GHICIA"]
] ;
And I'm trying to sort the array by making the second element equal to the first element of the next, like below:
arr = [
["AJATRN","PROPRI"],
["PROPRI","PORVEC"],
["PORVEC","GHICIA"],
["GHICIA","FOLELI"],
["FOLELI","BASMON"],
["BASMON","CALVI"]
]
The context is : these are somes sites with coordinates, I want to identify the order passed,
For exemple, I have [A,B] [C,D] [B,C] then I know the path is A B C D
I finally have one solution
var rs =[];
rs[0]=arr[0];
var hasAdded=false;
for (var i = 1; i < arr.length; i++) {
hasAdded=false;
console.log("i",i);
for (var j = 0, len=rs.length; j < len; j++) {
console.log("j",j);
console.log("len",len);
if(arr[i][1]===rs[j][0]){
rs.splice(j,0,arr[i]);
hasAdded=true;
console.log("hasAdded",hasAdded);
}
if(arr[i][0]===rs[j][1]){
rs.splice(j+1,0,arr[i]);
hasAdded=true;
console.log("hasAdded",hasAdded);
}
}
if(hasAdded===false) {
arr.push(arr[i]);
console.log("ARR length",arr.length);
}
}
But it's not perfect, when it's a circle like [A,B] [B,C] [C,D] [D,A]
I can't get the except answer

So I really hope this is what you like to achieve so have a look at this simple js code:
var vector = [
["PROPRI,PORVEC"],
["AJATRN,PROPRI"],
["BASMON,CALVI"],
["GHICIA,FOLELI"],
["FOLELI,BASMON"],
["PORVEC,GHICIA"]
]
function sort(vector) {
var result = []
for (var i = 1; i < vector.length; i++) result.push(vector[i])
result.push(vector[0])
return (result)
}
var res = sort(vector)
console.log(res)
Note: Of course this result could be easily achieved using map but because of your question I'm quite sure this will just confuse you. So have a look at the code done with a for loop :)

You can create an object lookup based on the first value of your array. Using this lookup, you can get the first key and then start adding value to your result. Once you add a value in the array, remove the value corresponding to that key, if the key has no element in its array delete its key. Continue this process as long as you have keys in your object lookup.
var vector = [["PROPRI", "PORVEC"],["AJATRN", "PROPRI"],["BASMON", "CALVI"],["GHICIA", "FOLELI"],["FOLELI", "BASMON"],["PORVEC", "GHICIA"]],
lookup = vector.reduce((r,a) => {
r[a[0]] = r[a[0]] || [];
r[a[0]].push(a);
return r;
}, {});
var current = Object.keys(lookup).sort()[0];
var sorted = [];
while(Object.keys(lookup).length > 0) {
if(lookup[current] && lookup[current].length) {
var first = lookup[current].shift();
sorted.push(first);
current = first[1];
} else {
delete lookup[current];
current = Object.keys(lookup).sort()[0];
}
}
console.log(sorted);

Select array index by object value

If I have an array like this:
var array = [{ID:1,value:'test1'},
{ID:3,value:'test3'},
{ID:2,value:'test2'}]
I want to select an index by the ID.
i.e, I want to somehow select ID:3, and get {ID:3,value:'test3'}.
What is the fastest and most lightweight way to do this?

Use array.filter:
var results = array.filter(function(x) { return x.ID == 3 });
It returns an array, so to get the object itself, you'd need [0] (if you're sure the object exists):
var result = array.filter(function(x) { return x.ID == 3 })[0];
Or else some kind of helper function:
function getById(id) {
var results = array.filter(function(x) { return x.ID == id });
return (results.length > 0 ? results[0] : null);
}
var result = getById(3);

With lodash you can use find with pluck-style input:
_.find(result, {ID: 3})

Using filter is not the fastest way because filter will always iterate through the entire array even if element being search for is the first element. This can perform poorly on larger arrays.
If you are looking for fastest way, simply looping through until the element is found might be best option. Something like below.
var findElement = function (array, inputId) {
for (var i = array.length - 1; i >= 0; i--) {
if (array[i].ID === inputId) {
return array[i];
}
}
};
findElement(array, 3);

I would go for something like this:
function arrayObjectIndexOf(myArray, property, searchTerm) {
for (var i = 0, len = myArray.length; i < len; i++) {
if (myArray[i].property === searchTerm)
return myArray[i];
}
return -1;
}
In your case you should do:
arrayObjectIndexOf(array, id, 3);

var indexBy = function(array, property) {
var results = {};
(array||[]).forEach(function(object) {
results[object[property]] = object;
});
return results
};
which lets you var indexed = indexBy(array, "ID");

Get the index of the object inside an array, matching a condition

I have an array like this:
[{prop1:"abc",prop2:"qwe"},{prop1:"bnmb",prop2:"yutu"},{prop1:"zxvz",prop2:"qwrq"},...]
How can I get the index of the object that matches a condition, without iterating over the entire array?
For instance, given prop2=="yutu", I want to get index 1.
I saw .indexOf() but think it's used for simple arrays like ["a1","a2",...]. I also checked $.grep() but this returns objects, not the index.

As of 2016, you're supposed to use Array.findIndex (an ES2015/ES6 standard) for this:
a = [
{prop1:"abc",prop2:"qwe"},
{prop1:"bnmb",prop2:"yutu"},
{prop1:"zxvz",prop2:"qwrq"}];
index = a.findIndex(x => x.prop2 ==="yutu");
console.log(index);
It's supported in Google Chrome, Firefox and Edge. For Internet Explorer, there's a polyfill on the linked page.
Performance note
Function calls are expensive, therefore with really big arrays a simple loop will perform much better than findIndex:
let test = [];
for (let i = 0; i < 1e6; i++)
test.push({prop: i});
let search = test.length - 1;
let count = 100;
console.time('findIndex/predefined function');
let fn = obj => obj.prop === search;
for (let i = 0; i < count; i++)
test.findIndex(fn);
console.timeEnd('findIndex/predefined function');
console.time('findIndex/dynamic function');
for (let i = 0; i < count; i++)
test.findIndex(obj => obj.prop === search);
console.timeEnd('findIndex/dynamic function');
console.time('loop');
for (let i = 0; i < count; i++) {
for (let index = 0; index < test.length; index++) {
if (test[index].prop === search) {
break;
}
}
}
console.timeEnd('loop');
As with most optimizations, this should be applied with care and only when actually needed.

How can I get the index of the object tha match a condition (without iterate along the array)?
You cannot, something has to iterate through the array (at least once).
If the condition changes a lot, then you'll have to loop through and look at the objects therein to see if they match the condition. However, on a system with ES5 features (or if you install a shim), that iteration can be done fairly concisely:
var index;
yourArray.some(function(entry, i) {
if (entry.prop2 == "yutu") {
index = i;
return true;
}
});
That uses the new(ish) Array#some function, which loops through the entries in the array until the function you give it returns true. The function I've given it saves the index of the matching entry, then returns true to stop the iteration.
Or of course, just use a for loop. Your various iteration options are covered in this other answer.
But if you're always going to be using the same property for this lookup, and if the property values are unique, you can loop just once and create an object to map them:
var prop2map = {};
yourArray.forEach(function(entry) {
prop2map[entry.prop2] = entry;
});
(Or, again, you could use a for loop or any of your other options.)
Then if you need to find the entry with prop2 = "yutu", you can do this:
var entry = prop2map["yutu"];
I call this "cross-indexing" the array. Naturally, if you remove or add entries (or change their prop2 values), you need to update your mapping object as well.

What TJ Crowder said, everyway will have some kind of hidden iteration, with lodash this becomes:
var index = _.findIndex(array, {prop2: 'yutu'})

var CarId = 23;
//x.VehicleId property to match in the object array
var carIndex = CarsList.map(function (x) { return x.VehicleId; }).indexOf(CarId);
And for basic array numbers you can also do this:
var numberList = [100,200,300,400,500];
var index = numberList.indexOf(200); // 1
You will get -1 if it cannot find a value in the array.

var index;
yourArray.some(function (elem, i) {
return elem.prop2 === 'yutu' ? (index = i, true) : false;
});
Iterate over all elements of array.
It returns either the index and true or false if the condition does not match.
Important is the explicit return value of true (or a value which boolean result is true). The single assignment is not sufficient, because of a possible index with 0 (Boolean(0) === false), which would not result an error but disables the break of the iteration.
Edit
An even shorter version of the above:
yourArray.some(function (elem, i) {
return elem.prop2 === 'yutu' && ~(index = i);
});

Using Array.map() and Array.indexOf(string)
const arr = [{
prop1: "abc",
prop2: "qwe"
}, {
prop1: "bnmb",
prop2: "yutu"
}, {
prop1: "zxvz",
prop2: "qwrq"
}]
const index = arr.map(i => i.prop2).indexOf("yutu");
console.log(index);

The best & fastest way to do this is:
const products = [
{ prop1: 'telephone', prop2: 996 },
{ prop1: 'computadora', prop2: 1999 },
{ prop1: 'bicicleta', prop2: 995 },
];
const index = products.findIndex(el => el.prop2 > 1000);
console.log(index); // 1

I have seen many solutions in the above.
Here I am using map function to find the index of the search text in an array object.
I am going to explain my answer with using students data.
step 1: create array object for the students(optional you can create your own array object).
var students = [{name:"Rambabu",htno:"1245"},{name:"Divya",htno:"1246"},{name:"poojitha",htno:"1247"},{name:"magitha",htno:"1248"}];
step 2: Create variable to search text
var studentNameToSearch = "Divya";
step 3: Create variable to store matched index(here we use map function to iterate).
var matchedIndex = students.map(function (obj) { return obj.name; }).indexOf(studentNameToSearch);
var students = [{name:"Rambabu",htno:"1245"},{name:"Divya",htno:"1246"},{name:"poojitha",htno:"1247"},{name:"magitha",htno:"1248"}];
var studentNameToSearch = "Divya";
var matchedIndex = students.map(function (obj) { return obj.name; }).indexOf(studentNameToSearch);
console.log(matchedIndex);
alert("Your search name index in array is:"+matchedIndex)

You can use the Array.prototype.some() in the following way (as mentioned in the other answers):
https://jsfiddle.net/h1d69exj/2/
function findIndexInData(data, property, value) {
var result = -1;
data.some(function (item, i) {
if (item[property] === value) {
result = i;
return true;
}
});
return result;
}
var data = [{prop1:"abc",prop2:"qwe"},{prop1:"bnmb",prop2:"yutu"},{prop1:"zxvz",prop2:"qwrq"}]
alert(findIndexInData(data, 'prop2', "yutu")); // shows index of 1

function findIndexByKeyValue(_array, key, value) {
for (var i = 0; i < _array.length; i++) {
if (_array[i][key] == value) {
return i;
}
}
return -1;
}
var a = [
{prop1:"abc",prop2:"qwe"},
{prop1:"bnmb",prop2:"yutu"},
{prop1:"zxvz",prop2:"qwrq"}];
var index = findIndexByKeyValue(a, 'prop2', 'yutu');
console.log(index);

Try this code
var x = [{prop1:"abc",prop2:"qwe"},{prop1:"bnmb",prop2:"yutu"},{prop1:"zxvz",prop2:"qwrq"}]
let index = x.findIndex(x => x.prop1 === 'zxvz')

Another easy way is :
function getIndex(items) {
for (const [index, item] of items.entries()) {
if (item.prop2 === 'yutu') {
return index;
}
}
}
const myIndex = getIndex(myArray);

Georg have already mentioned ES6 have Array.findIndex for this.
And some other answers are workaround for ES5 using Array.some method.
One more elegant approach can be
var index;
for(index = yourArray.length; index-- > 0 && yourArray[index].prop2 !== "yutu";);
At the same time I will like to emphasize, Array.some may be implemented with binary or other efficient searching technique. So, it might perform better over for loop in some browser.

Why do you not want to iterate exactly ? The new Array.prototype.forEach are great for this purpose!
You can use a Binary Search Tree to find via a single method call if you want. This is a neat implementation of BTree and Red black Search tree in JS - https://github.com/vadimg/js_bintrees - but I'm not sure whether you can find the index at the same time.

One step using Array.reduce() - no jQuery
var items = [{id: 331}, {id: 220}, {id: 872}];
var searchIndexForId = 220;
var index = items.reduce(function(searchIndex, item, index){
if(item.id === searchIndexForId) {
console.log('found!');
searchIndex = index;
}
return searchIndex;
}, null);
will return null if index was not found.

var list = [
{prop1:"abc",prop2:"qwe"},
{prop1:"bnmb",prop2:"yutu"},
{prop1:"zxvz",prop2:"qwrq"}
];
var findProp = p => {
var index = -1;
$.each(list, (i, o) => {
if(o.prop2 == p) {
index = i;
return false; // break
}
});
return index; // -1 == not found, else == index
}

Issues with javascript splice

I have a small piece of code in which i'm trying to splice an item from an array. In below code it should remove item which has "Javascript" and the resulting array should contain only "Java". What am i doing wrong here ?
var autoCompleteArray = new Array();
var item = new Array();
item.push("1");
item.push("Java");
autoCompleteArray.push(item);
var item2 = new Array();
item2.push("2");
item2.push("Javascript");
autoCompleteArray.push(item2);
var val = "Javascript";
for(var i=0;i<autoCompleteArray.length;i++){
if(autoCompleteArray[i][1] == val) {
autoCompleteArray.splice(autoCompleteArray[i],1);
}
}
console.log(autoCompleteArray); //Should show Java in the array since Javascript item has been removed.

You're splicing the wrong thing; this should work:
if(autoCompleteArray[i][1] == val) {
autoCompleteArray.splice(i,1);
}
The first argument to .splice() is the index, not the value at that index.
Be aware that when you splice at index i, for that iteration you should not increase i:
var i = 0;
while (i < autoCompleteArray.length) {
if(autoCompleteArray[i][1] == val) {
autoCompleteArray.splice(i, 1);
continue;
}
++i;
}
This is fine if there can be only one match of course, in which case you can also break; out of the loop.

As #Jack mentioned you need to pass an index (not a value) to splice. I would rewrite your loop as:
for (var i = 0; i < autoCompleteArray.length; i++) {
if (autoCompleteArray[i][1] === val) {
autoCompleteArray.splice(i--, 1);
}
}
That should solve your problem. See the demo here: http://jsfiddle.net/7PM94/
Also note that you can create arrays using the literal syntax instead of pushing elements. You can define autoCompleteArray as follows:
var autoCompleteArray = [
["1", "Java"],
["2", "JavaScript"]
];
Hope that helps.

Search multi-dimensional array JavaScript

I have an array which looks like this :
selected_products[0]=["r1","7up",61,"Albertsons"]
selected_products[1]=["r3", "Arrowhead",78,"Arrowhead "]
selected_products[2]=["r8", "Betty Crocker Cake Mix (Variety)",109,"Arrowhead "]
...
how can I search for an item in this array according to the first entry in each item (r1,r2,..)
the array is huge I am looking for a fast an effective way to get results from this array
I used the JQuery function jQuery.inArray but it couldn't find any thing in my array , I used it this way :
alert($.inArray(["r1","7up",61,"Albertsons"],selected_products))// it returns -1
alert($.inArray("r1",selected_products))//this also returns -1

If you want it to be fast, you'll want a for loop so that you can break the loop when the match is found.
var result;
for( var i = 0, len = selected_products.length; i < len; i++ ) {
if( selected_products[i][0] === 'r1' ) {
result = selected_products[i];
break;
}
}
Of course this assumes there's only one match.
If there's more than one, then you could use $.grep if you want jQuery:
var result = $.grep(selected_products, function(v,i) {
return v[0] === 'r1';
});
This will give you a new Array that is a subset of the matched items.
In a similar manner, you could use Array.prototype.filter, if you only support modern JavaScript environments.
var result = selected_products.filter(function(v,i) {
return v[0] === 'r1';
});
One other solution would be to create an object where the keys are the rn items. This should give you a very fast lookup table.
var r_table = {};
for( var i = 0, len = selected_products.length; i < len; i++ ) {
r_table[selected_products[i][0]] = selected_products[i];
}
Then do your lookups like this:
r_table.r4;
Again this assumes that there are no duplicate rn items.

So you are trying to find the index of the matched result?, well that changes the things a little bit:
var index=-1;
for(var i = 0, len = selected_products.length; i < len; i++){
if(selected_products[i][0] === "r1"){
index = i;
break;
}
}
if(index > -1){
alert(selected_products[index].join(","));//"r1,7up,61,Albertsons"
}
Note: This will return the first result matched, if you want to get an array containing a list of all indexes:
var results=[];
for(var i = 0, len = selected_products.length; i < len; i++){
if(selected_products[i][0] === "r1"){
results.push(i);
}
}
You can then call (for example) the last 'r1' matched like this selected_products[results[results.length-1]].join(",");

Just to pick up #am not i am's great input. Here is a live example. He solved it. I just wanted to give an example that it works. Hope it helps. This puts the values found from the selected value in 2 input fields.
http://jsfiddle.net/asle/ZZ78j/2/
$(document).ready(function () {
var liste = [];
liste[0] = ["First Name", "12345678", "first.name#testdomain.no"];
liste[1] = ["Second Name", "20505050", "second.nametestdomain.no"];
liste[2] = ["", "", ""];
$("#selger").change(function () {
var valg = ($(this).val());
var telefon;
var epost;
for (var i = 0, len = liste.length; i < len; i++) {
if (liste[i][0] === valg) {
telefon = liste[i][1];
epost = liste[i][2];
$("#tel").val(telefon);
$("#epost").val(epost);
break;
}
}
});
});

Try this,
// returns the index of inner array, if val matches in any array
function findIn2dArray(arr_2d, val){
var indexArr = $.map(arr_2d, function(arr, i) {
if($.inArray(val, arr) != -1) {
return 1;
}
return -1;
});
return indexArr.indexOf(1);
}
function test(){
alert(findIn2dArray(selected_products, 'r8'));
}

You might wanna consider not doing these things in Javascript but in a server sided language (PHP/Java/.NET). In this way you:
Won't have problems with browser incapabilities (Mostly IE errors)
Shorter Javascript code and therefore faster to load.
Your site also works with Javascript turned off.
An example how to do this in PHP:
<?php
function search($array, $key, $value)
{
$results = array();
if (is_array($array))
{
if (isset($array[$key]) && $array[$key] == $value)
$results[] = $array;
foreach ($array as $subarray)
$results = array_merge($results, search($subarray, $key, $value));
}
return $results;
}
?>

You may create index object { r1: 1, r2: 2,..., < search key >: < element index >, ...} and use it for searching.