在数组数组中找到最长数组的索引 [英] Find the index of the longest array in an array of arrays

问题描述

如果您的数组包含不确定数量的数组

If you have an array containing an indefinite amount of arrays

例如:

var masterArray = [ [1,2,3,4,5],
                    [1,2], 
                    [1,1,1,1,2,2,2,2,4,4],
                    [1,2,3,4,5] ];

在masterArray中找到最长数组索引的有效方法是什么? (在此示例中，索引为2).

What is an efficient way to find the index of the longest array in masterArray? (in this example index would be 2).

推荐答案

var masterArray = [ [1,2,3,4,5],
                    [1,2], 
                    [1,1,1,1,2,2,2,2,4,4],
                    [1,2,3,4,5] ];

单线是:

masterArray.map(function(a){return a.length;}).indexOf(Math.max.apply(Math, masterArray.map(function(a){return a.length;})));

但是更好地缓存map结果.

var lengths = masterArray.map(function(a){return a.length;});
lengths.indexOf(Math.max.apply(Math, lengths));

注意，即使这段代码也对数组进行3次迭代(分别为map，max，indexOf).
为了提高效率，您应该手动迭代数组.

Note, even this code iterate array 3 times(map, max, indexOf separately).
For more efficient you should manual iterate array.

var max = -Infinity;
var index = -1;
masterArray.forEach(function(a, i){
  if (a.length>max) {
    max = a.length;
    index = i;
  }
});

---

Reduce方法:

---

Reduce method:

masterArray.reduce(function(maxI,el,i,arr) {return el.length>arr[maxI].length ? i : maxI;}, 0)

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