If you have an array containing an indefinite amount of arrays
ex:
var masterArray = [ [1,2,3,4,5],
[1,2],
[1,1,1,1,2,2,2,2,4,4],
[1,2,3,4,5] ];
What is an efficient way to find the index of the longest array in masterArray? (in this example index would be 2).
One-liner is:
masterArray
.map(a=>a.length)
.indexOf(Math.max(...masterArray.map(a=>a.length)));
But better to cache masterArray.map(a=>a.length) results.
const lengths = masterArray.map(a=>a.length);
lengths.indexOf(Math.max(...lengths));
Note, this code still iterate array at least* 3 times(map, max, indexOf separately).
*Spread operator is for readability and can be omitted
For more efficiency you should manual iterate array.
let max = -Infinity;
let index = -1;
masterArray.forEach(function(a, i){
if (a.length > max) {
max = a.length;
index = i;
}
});
Reduce method:
masterArray.reduce((maxI,el,i,arr) =>
(el.length>arr[maxI].length) ? i : maxI, 0);
