How to get an array of values based on an array of indexes?

Question

I have a set of two arrays. One contains some fruit values as strings, the other one contains some random numbers. Here I considered the number arrays are the indexes of the fruits array. How to get a new array of fruits given the numbers in the index array?

Sample code:

var resultArr = [];
var fruitier = ["apple", "orange", "grapes", "pineapple", "fig", "banana", "jackfruit", "pomegranate"];
var indexArr = [0, 2, 4];

Output:

resultArr = ["apple", "grapes", "fig"];

Solution 1

for(var i = 0; i < indexArr.length; i++)
  resultArr.push(fruitier[indexArr[i]]);

Solution 2

Use .map:

let resultArr = indexArr.map(i => fruitier[i])

Solution 3

If you want to achieve that with lodash, use _.at():

var fruitier = ['apple', 'orange', 'grapes', 'pineapple', 'fig', 'banana', 'jackfruit', 'pomegranate'];
var indexArr = [0, 2, 4];
var resultArr = _.at(fruitier, indexArr);

console.log(resultArr);

<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.16.6/lodash.min.js"></script>

Solution 4

Array#map works (documentation)

const getFromIndex = (array, indexes) => indexes.map((index) => array[index]);

You can use Array#filter too (documentation)

const fruitier = ['apple', 'orange', 'grapes', 'pineapple', 'fig',   'banana', 'jackfruit', 'pomegranate'];
const indexArr = [0, 2, 4];  

const getFromIndex = (array, indexes) => {
  return array.filter((element, index) => indexes.includes(index)); 
};

Or also Array#reduce (documentation)

const getFromIndex = (array, indexes) => {
    return indexes.reduce((result, i) => result.concat(array[i]), []); 
};

Solution 5

Use lodash pullAt

var fruitier = ["apple", "orange", "grapes", "pineapple", "fig", "banana", 
"jackfruit", "pomegranate"];
var indexArr = [0, 2, 4];
var resultArr = _.pullAt(fruitier, indexArr);
console.log(resultArr);
// ["apple", "grapes", "fig"]

<script src="https://cdn.jsdelivr.net/npm/[email protected]/lodash.min.js"></script>

Key difference to be aware of alongside the above recommendation for _.at() is - this method mutates input array.

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Comments

[elquimista]

Just be aware that if you use flow type, it will complain because _.at() expects the first argument to be of Object, not Array. I think it's fine to ignore it using // $FlowFixMe