Develop Reference

How to concatenate values of duplicate keys

When reading a csv into a javascript dictionary, how can I concatenate values of what would otherwise be duplicate keys? I've seen answers for how to do this with bash, c#, and perl, but I haven't been able to find answers for Javascript. Here's what I have:
var subjects = {};
d3.csv("test.csv", function(data) {
for (var i = 0; i < data.length; i++)
{
subjects[data[i].Id] = data[i].VALUE;
}
console.log(subjects);
});
This, obviously writes over existing keys. Instead, I want the key to be an array of the values. The csv basically looks like:
Id, VALUE
id1, subject1
id2, subject1
id1, subject3
And I want to output as:
{"id1": ["subject1", "subject3"], "id2": ["subject1"]...}

Just check if your output already has the key, if so you add the new value to the array. Else you create an array.
d3.csv("test.csv", function(data) {
var subjects = {};
for (var i = 0; i < data.length; i++)
{
// Check if key already exists
if(subjects.hasOwnProperty(data[i].Id)){
// push data to array
subjects[data[i].Id].push(data[i].VALUE);
}else{
// create new key and array
subjects[data[i].Id] = [data[i].VALUE];
}
}
console.log(subjects);
});

You could make it into an array and then push the content into that array
var subjects = {};
d3.csv("test.csv", function(data) {
for (var i = 0; i < data.length; i++)
{
//first time we see this id, turn it into an array
if(typeof subjects[data[i].Id] != "object"){
subjects[data[i].Id] = [];
}
//push content to the array
subjects[data[i].Id].push(data[i].VALUE);
}
console.log(subjects);
});

Try this inside the for loop:
typeof subjects[data[i].Id] == 'undefined' && (subjects[data[i].Id] = []);
subjects[data[i].Id].push(data[i].VALUE);

You can reduce the footprint of your code slightly if you use reduce:
var out = data.reduce((p, c) => {
const id = c.Id;
p[id] = p[id] || [];
p[id].push(c.VALUE);
return p;
}, {});
RESULT
{
"id1": [
"subject1",
"subject3"
],
"id2": [
"subject1"
]
}
DEMO

How to access elements of arrays within array (JavaScript)?

I'm trying to access elements from a JavaScript array:
[["1","John"],["2","Rajan"],["3","Hitesh"],["4","Vin"],["5","ritwik"],["6","sherry"]]
I want to access
1, 2, 3, 4, 5, 6 separately in a variable and John, Rajan, Hitesh, Vin, Ritwik, Sherry separately in a variable.
I tried converting it to a string and split(), but it doesn't work.
this is code i tried
var jArray = <?php echo json_encode($newarray); ?> ;
var nJarr = jArray[0]; nJarr.toString();
var res = nJarr.split(","); var apname = res[0];
alert(apname);
but there's no alert appearing on the screen

If you are open to using Underscore, then it's just
var transposed = _.zip.apply(0, arr);
and the arrays you are looking for will be in transposed[0] and transposed[1].
You can write your own transpose function fairly easily, and it's more compact if you can use ES6 syntax:
transpose = arr => Object.keys(arr[0]).map(i => arr.map(e => e[i]));
>> transpose([["1","John"], ["2","Rajan"], ...]]
<< [[1, 2, ...], ["John", "Rajan", ...]]
If you want an ES5 version, here's one with comments:
function transpose(arr) { // to transpose an array of arrays
return Object.keys(arr[0]) . // get the keys of first sub-array
map(function(i) { // and for each of these keys
arr . // go through the array
map(function(e) { // and from each sub-array
return e[i]; // grab the element with that key
})
))
;
}
If you prefer old-style JS:
function transpose(arr) {
// create and initialize result
var result = [];
for (var i = 0; i < arr[0].length; i++ ) { result[i] = []; }
// loop over subarrays
for (i = 0; i < arr.length; i++) {
var subarray = arr[i];
// loop over elements of subarray and put in result
for (var j = 0; j < subarray.length; j++) {
result[j].push(subarray[j]);
}
}
return result;
}

Do it like bellow
var arr = [["1","John"],["2","Rajan"],["3","Hitesh"],["4","Vin"],["5","ritwik"],["6","sherry"]];
var numbers = arr.map(function(a){return a[0]}); //numbers contain 1,2,3,4,5
var names = arr.map(function(a){return a[1]}); //names contain John,Rajan...

Try this:
var data = [["1","John"],["2","Rajan"],["3","Hitesh"],["4","Vin"],["5","ritwik"],["6","sherry"]];
var IDs = [];
var names = [];
for(i=0; i<data.length; i++)
{
IDs.push(data[i][0]);
names.push(data[i][1]);
}
console.log(IDs);
console.log(names);
Here is the working fiddle.

Get full value from array using partial value

I have an array like this:
var array = ["xs-1", "sm-10", "md-4"];
Now I want to get the number at the end of a particular value. For example I want to search the array for "md-" and see what number is at the end of that string (should return 4).
I can't do array.indexOf("xs-") because that isn't the whole value. Is there a way to do this?

Using a for loop:
var array = ["xs-1", "sm-10", "md-4"];
var search = "md-";
var found = null;
for (var i = 0; i < array.length; i++) {
if (array[i].indexOf(search) === 0) {
found = array[i];
break; // Note: this is assuming only one match exists - or at least you are
// only interested in the first match
}
}
if (found) {
alert(found);
} else {
alert("Not found");
}
Using .filter:
var array = ["xs-1", "sm-10", "md-4"];
var search = "md-";
var filtered = array.filter(function(item) {
return item.indexOf(search) === 0;
});
// note that here filtered will contain all matched elements, so it might be more than
// one match.
alert(filtered);
Building from #János Weisz's suggestion, you can easily transform your array into an object using .reduce:
var array = ["xs-1", "sm-10", "md-4"];
var search = "md";
var obj = array.reduce(function(prev, item) {
var cells = item.split("-");
prev[cells[0]] = cells[1];
return prev;
}, {});
// note: at this point we have an object that looks like this:
// { xs:1, sm:10, md: 4 }
// if we save this object, we can do lookups much faster than looping
// through an array
// now to find "md", we simply do:
alert(obj[search]);
If you need to do multiple look ups from the same source array, then transforming it into an object may be the most efficient approach overall. You pay the initial price of the transformation, but after than lookups are O(1) versus O(n) for each time you have to search your array. Of course, if you only ever need one item, then probably don't bother.

I recommend using objects for this:
var array = [{'type': 'xs', 'value': 1}, {'type' : 'sm', 'value': '10'}, {'type' : 'md', 'value': '4'}];
This way you can search the array as:
function searchMyArrayByType(array, type) {
var items[];
for (var i = 0; i < array.length; i++)
{
if (array[i].type == type) items.push(array[i].value);
}
return items;
}
var valuesWithMd = searchMyArrayByType(array, 'md');
For more information regarding the structure and use of objects, please refer to https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Working_with_Objects

You can create a method that takes the prefix you're looking for, the array, and the split character and returns all the numbers in an array:
function findNumberFromPrefix(prefix, arr, splitChar) {
var values = [];
for (var i = 0; i < arr.length; i++) {
if (arr[i].indexOf(prefix) === 0) {
values.push(arr[i].split(splitChar)[1]);
}
}
return values;
}
And call it:
var array = ["xs-1", "sm-10", "md-4"];
var values = findNumberFromPrefix("md-", array, "-");
console.log(values); //["4"]
Demo: http://jsfiddle.net/rn4h9msh/

A more functional approach and assuming you can have have more than one element with the same prefix:
function findPrefix(array, prefix) {
return array.filter(function (a) { return a.indexOf(prefix) === 0; })
.map(function (e) { return e.slice(prefix.length); })
}

If you have only one matching element, do a loop like this:
var array = ["xs-1", "sm-10", "md-4"];
var needle = "md-";
for(i=0;i<array.length;i++) {
if(array[i].indexOf(needle) == 0)
alert(array[i].substr(needle.length, array[i].length));
}
Demo: http://jsfiddle.net/kg0c43ov/

You can do it like this...
var array = ["xs-1", "sm-10", "md-4"];
getValue("md-");
function getValue(search) {
for(var key in array) {
if(array[key].indexOf(search) > -1) {
alert("Array key is: " + key);
alert("Array value is: " + array[key].replace(search, ""));
}
}
}
JSFiddle here.

splitting array elements in javascript split function

Hi i have the below array element
var array =["a.READ","b.CREATE"]
I'm trying to split the elements based on "." using javascript split method
below is my code
var array1=new Array();
var array2 = new Array();
for (var i = 0; i < array .length; i++) {
array1.push(array [i].split("."));
}
console.log("this is the array1 finish ----"+array1)
The out put that i'm receiving is
[["a","READ"],["b","CREATE"]]
The expected output that i want is
array1 =["a","b"]
array2=["READ","CREATE"]
I'm stuck here any solution regarding this is much helpful

You need to add to array2 and use both elements from the returned array that String.prototype.split returns - i.e. 0 is the left hand side and 1 is the right hand side of the dot.
var array = ["a.READ", "b.CREATE"]
var array1 = []; // better to define using [] instead of new Array();
var array2 = [];
for (var i = 0; i < array.length; i++) {
var split = array[i].split("."); // just split once
array1.push(split[0]); // before the dot
array2.push(split[1]); // after the dot
}
console.log("array1", array1);
console.log("array2", array2);

We'll start off with a generic transpose function for two-dimensional arrays:
function transpose(arr1) { // to transpose a 2d array
return arr1[0].map( // take the first sub-array and map
function(_, i) { // each element into
return arr1.map( // an array which maps
function(col) { // each subarray into
return col[i]; // the corresponding elt value
}
);
}
);
}
Now the solution is just
transpose( // transpose the two-dimensional array
array.map( // created by taking the array and mapping
function(e) { // each element "a.READ" into
return e.split('.'); // an array created by splitting it on '.'
}
)
)

You are adding nothing to array2. Please use indexes properly , like below:
var array1=new Array();
var array2 = new Array();
for (var i = 0; i < array .length; i++) {
array1.push(array [i].split(".")[0]);
array2.push(array [i].split(".")[1]);
}

you can do something like this
var array =["a.READ","b.CREATE"];
var arr1= [], arr2= [];
array.forEach(function(item,index,arr){
item.split('.').forEach(function(item,index,arr){
if(index % 2 === 0){
arr1.push(item);
}else{
arr2.push(item);
}
});
});
console.log(arr1);
console.log(arr2);
DEMO

I guess this is a bit redundant but, the split method actually returns and array. Although your code was off you were not modifying array2. Consider the following.
var array = [ "a.READ" , "b.CREATE" ]
, array1 = []
, array2 = []
// cache array length
, len = array.length;
for ( var i = 0; i < len; i++ ) {
// the split method returns a new array
// so we will cache the array
// push element 0 to array1
// push element 1 to array2
var newArr = array[ i ].split('.');
array1.push( newArr[ 0 ] );
array2.push( newArr[ 1 ] );
}
console.log( 'array1: ', array1 );
console.log( 'array2: ', array2 );

Use this:
for (var i = 0; i < array .length; i++) {
var parts = array[i].split('.');
array1.push(parts[0]);
array2.push(parts[1]);
}

You have not assigned any value to Array2. You can do as shown below.
var array1=[];
var array2 = [];
for (var i = 0; i < array .length; i++) {
var arrayTemp=[];
arrayTemp.push(array [i].split("."));
array1.push(arrayTemp[0]);
array2.push(arrayTemp[1]);
}

Objects within an Array

I have multiple objects like the one below, and I was wondering what the correct syntax would be for putting them all within a single array. I'm also wondering how to correctly cycle through all of the arrays.
var verbMap = [
{
infinitive: "gehen",
thirdPres: "geht",
thirdPast: "ging",
aux: "ist",
pastPart: "gegangen",
english: "go"
},
{
infinitive: "gelingen",
thirdPres: "gelingt",
thirdPast: "gelang",
aux: "ist",
pastPart: "gelungen",
english: "succeed"
}
];
I know the correct way to cycle through that above array is:
for(v in verbMap){
for(p in verbMap[v]){
}
}
If I wanted to cycle through a larger array holding multiple arrays like verbMap, what would be the correct way to do that?

Just put the verbMap arrays in another array.
var verbMaps = [verbMap1, verbMap2...]
The key thing to understand is that your verbMap is an array of object literals. Only use
for (k in verbMap)...
for object literals.
The correct way to loop thru an array is something like
for (var i = 0; i < verbMaps.length; i++) {
var currentVerbMap = verbMaps[i];
for (var j = 0; j < currentVerbMap.length; j++) {
var currentHash = currentVerbMap[j];
for (var k in currentHash) {
console.log(k, currentHash[k];
}
}
}

The following function outputs every value from a (possibly) infinite array given as a parameter.
function printInfiniteArray(value){
if (value instanceof Array){
for(i=0;i<value.length;i++){
printInfiniteArray(value[i]);
}
} else {
console.log(value);
}
}
Edited code. Thanks jtfairbank

Your array does not contain other arrays. It contains objects. You could try this to loop though it.
for(var i = 0; i < verbMap.length; i++)
{
var obj = verbMap[i];
alert("Object #"+ i " - infinitive: " + obj.infinitive);
}

You would treat the array like any other javascript object.
var arrayOfArrays = [];
var array1 = ["cows", "horses", "chicken"];
var array2 = ["moo", "neigh", "cock-adoodle-doo"];
arrayOfArrays[0] = array1;
arrayOfArrays[1] = array2;
You can also use javascript's literal notation to create a multi-dimentional array:
var arrayOfArrays = [ ["meat", "veggies"], ["mmmm!", "yuck!"] ];
To cycle through the array of arrays, you'll need to use nested for loops, like so:
for (var i = 0; i < arrayOfArrays.length; i++) {
var myArray = arrayOfArrays[i];
for (var j = 0; j < myArray.length; j++) {
var myData = myArray[0]; // = arrayOfArrays[0][0];
}
}
DO NOT USE For...in!!!
That is not what it was made for. In javascript, For...in can have some unwanted behaviors. See Why is using "for...in" with array iteration a bad idea? for more detail.

You can use jQuery.each to cycle through an array or object, without having to check which one it is. A simple recursive function to cycle through key-value pairs in a nested structure, without knowing the exact depth:
var walk = function(o) {
$.each(o, function(key, value) {
if (typeof value == 'object') {
walk(value);
} else {
console.log(key, value);
}
});
}