使用JavaScript查找数组中最大的重复值

Question

I have an array with repeating values:

[0, 1, 6, 0, 1, 0]

What is an efficient way to return the highest amount that a specific value repeats?

In the example array I would want the script to return 3 because the number 0 repeats the most often and it repeats 3 times. I'm already using jQuery and Underscore.

Answer 1

If you use lodash ...

_.max(_.countBy(a,_.identity))

More about lodash: http://lodash.com/

Answer 2

This is similar to the basic approach, but utilizes underscore's reduce and max functions. If you had a really really really large array, I hope it's clear how you could parallelize this with a map phase before the reduce.

var arr = [1,0,2,3,4,0,3,0];
var counts = _.reduce(arr, function(counts, val) {
    if (counts[val]) {
        counts[val]++;
    } else {
        counts[val] = 1;
    }
    return counts;
}, {});
return _.max(counts);

Answer 3

Yay, this is like a google interview question lol. I would recommend looping through your array once and maintaining an associative array of each element as you encounter it in the while incrementing a counter.

For example:

http://jsfiddle.net/btKjX/

var a = [0, 0 , 2, 2, 3, 3, 3, 3];
var counts = {};

for(var i = 0, il = a.length; i < il; i++){
    var num = a[i];

    if(typeof counts[num] === 'undefined'){
        counts[num] = 0;
    }

    counts[num]++;
}

var max = -1;

for(var c in counts){
    if(counts[c] > max){
        max = counts[c];
    }
}

console.log(max);

Answer 4

a hacky way might be to sort it, split it on every value change and then look at the length of each string, but let's try something more reasonable:

var nums = [0, 1, 6, 0, 1, 0]
var occurence = {}
$.each(nums, function(a, num_id) {
  if (occurence[num_id] != null) {
    occurence[num_id]++;
  } else {
    occurence[num_id] = 1;
  }
});

occurence would then have the number of occurences of every value in nums, with the number itself being the key.