Array transformation/manipulation

Question

I have one array like this one:

array1=[{value:1, label:'value1'},{value:2, label:'value2'}, {value:3, label:'value3'}]

I have a second array of integer :

array2=[1,3]

I would like to obtain this array without a loop for :

arrayResult = ['value1', 'value3']

Does someone know how to do it with javascript ?

Thanks in advance

Answer 1

Map the elements in array2 to the label property of the element in array1 with the corresponding value:

array2                      // Take array2 and
  .map(                     // map
    function(n) {           // each element n in it to
      return array1         // the result of taking array1
        .find(              // and finding
          function(e) {     // elements
            return          // for which 
              e.value       // the value property
              ===           // is the same as 
              n;            // the element from array2
          }
        )
        .label              // and taking the label property of that elt
      ;
    }
  )
;

Without comments, and in ES6:

array.map(n => array1.find(e => e.value === n).label);

Answer 2

Good answers all. If I may suggest one more alternative using Map as this seems to be suited to a key:value pair solution.

var arr1 = [ {value:1, label:'value1'}, {value:2, label:'value2'}, {value:3, label:'value3'} ];
var arr2 = [1, 3];

// create a Map of the first array making value the key.
var map = new Map( arr1.map ( a => [a.value, a.label] ) );

// map second array with the values of the matching keys
var result = arr2.map( n => map.get ( n ) );

Of course this supposes that the key:value structure of the first array will not become more complex, and could be written in the simpler form of.

var arr1 = [[1,'value1'], [2,'value2'], [3,'value3']]; // no need for names
var arr2 = [1, 3];

var map = new Map( arr1 ); // no need to arr1.map ;
var result = arr2.map( n => map.get ( n ) );

Answer 3

Just index the first array using the _.indexBy function:

var indexedArray1 = _.indexBy(array1, "value");
_.map(array2, function(x) { return indexedArray1[x].label; });

Answer 4

You can use .filter and .map, like this

var array1 = [
    {value:1, label:'value1'},{value:2, label:'value2'}, {value:3, label:'value3'}
];

var array2 = [1, 3];

var arrayResult = array1.filter(function (el) {
  return array2.indexOf(el.value) >= 0;
}).map(function (el) {
  return el.label;
});

console.log(arrayResult);

Answer 5

A simple for-loop should suffice for this. In the future you should seriously post some code to show what you have tried.

var array1=[{value:1, label:'value1'},{value:2, label:'value2'}, {value:3, label:'value3'}];
var array2=[1,3];
var result = [];

for (var i = 0; i < array2.length; i++){
  result.push(array1[array2[i]-1].label);
}
console.log(result); //["value1", "value3"]

JSBIN