Get specific items from array

Question

What I need is to get specific items (defined by array if indices) from an array. Let say I have this source array [2,4,1,6,8] and this array of indices [0,3] and I want the result to be [2,6]. So far I am doing this to achieve the result

var iter = -1;
source.filter(function(item) {iter++; if (indices.indexOf(iter)>-1) {return item}})

Is there any more elegant solution (maybe some javascript syntactic sugar I am not aware of) than this?

Answer 1

There is no syntactic sugar for this particular task, but a simpler way would be:

var destination = [];
indices.forEach(function(index) {
 destination.push(source[index]);
});

Answer 2

You can use map:

var source = [2, 4, 1, 6, 8];
var indices = [0, 3];
var output = indices.map(function(i){
 return source[i]
});

Answer 3

It's probably best to check if the original array has the index before trying to access it.

var original = [1,2,3,4,5,6,7,8,9,10];
var indicesSafe = [2,6];
var indicesUnsafe = [2,1234];
function filter(original, indices) {
 var result = [];
 for (var i = 0; i < indices.length; i++) {
 var index = indices[i];
 
 // Check if index exists
 if (original.length > index) {
 
 // If so push onto return value
 result.push(original[index]);
 }
 }
 return result;
}
// Safe
var resultSafe = filter(original, indicesSafe);
// Unsafe
var resultUnsafe = filter(original, indicesUnsafe);
document.getElementById('output').innerHTML += JSON.stringify(resultSafe);
document.getElementById('output').innerHTML += "\n" + JSON.stringify(resultUnsafe);

<pre id="output"></pre>

Answer 4

This is what I would do:

var dataArray = [2,4,1,6,8];
var indicesArray = [0,3];
var resultArray = [];
for (var i=0; i<indicesArray.length; i++) {
 resultArray.push(dataArray[i]);
}

Answer 5

If you're considering a library you can use lodash _.at

_.at(['a', 'b', 'c'], [0, 2]);
// → ['a', 'c']
_.at(['barney', 'fred', 'pebbles'], 0, 2);
// → ['barney', 'pebbles']