What is the quickest way to compare two arrays and return a third array containing the values from array2 where the associated values from array1 are true?
const array1 = [true, false, false, true];
const array2 = ['a', 'b', 'c', 'd'];
The result should be:
const result = ['a', 'd'];
Use filter.
const array1 = [true, false, false, true];
const array2 = ['a', 'b', 'c', 'd'];
const res = array2.filter((_, i) => array1[i]);
console.log(res);ES5 syntax:
var array1 = [true, false, false, true];
var array2 = ['a', 'b', 'c', 'd'];
var res = array2.filter(function(_, i) {
return array1[i];
});
console.log(res);Filter function is slower than for loop. The quicker option is to use for loop with or without ternary operator.. It is faster than the filter function.
I've include a code snippet that shows how long each option takes.
const array1 = [true, false, false, true];
const array2 = ['a', 'b', 'c', 'd'];
// filter
console.time('filter');
const result1 = array2.filter((_, i) => array1[i]);
console.timeEnd('filter');
console.log(result1);
// for loop with ternary operator
console.time('forLoopWithTernary');
const result2 = [];
for(let i = 0; i < array2.length; i++){
(array1[i]) ? result2.push(array2[i]) : null;
}
console.timeEnd('forLoopWithTernary');
console.log(result2);
// for loop w/o ternary operator
console.time('forLoopWithoutTernary');
const result3 = [];
for(let i = 0; i < array2.length; i++){
if(array1[i])
result3.push(array2[i]);
}
console.timeEnd('forLoopWithoutTernary');
console.log(result3);
.filter…
filter as well; however, the OP did ask for the quickest way. On my end, I get 0.060ms for filter, 0.010ms for forLoopWithTernary, and 0.010ms for forLoopWithoutTernary. The time do change on each run.. Not much of difference I admit, but it is as OP requested.You can use array.reduce:
var array1 = [true, false, false, true];
var array2 = ['a', 'b', 'c', 'd'];
console.time('reduce');
var res = array1.reduce((total, currentValue, index) => {
return currentValue ? [...total, array2[index]] : total;
}, []);
console.log(res);
console.timeEnd('reduce');