how to get mode in array

问题

I have wounder`d for a while about how to get mode in array. That elements that are the same in array would be put together. For ex. [Alex, Steven, Georg, Alice, Alex, Georg]; return would be: Alex: 2, Steven: 1, Georg: 2, Alice:1;

I wrote the code but it works only for numbers from 1 to 10. And for sure there is a better way.

(I don`t think you need my code but will paste it anyway.)

var mode = function (data){
            var result1 = data.filter(function (verde) {return verde === 1});
            var result2 = data.filter(function (verde) {return verde === 2});
            var result3 = data.filter(function (verde) {return verde === 3});
            var result4 = data.filter(function (verde) {return verde === 4});
            var result5 = data.filter(function (verde) {return verde === 5});
            var result6 = data.filter(function (verde) {return verde === 6});
            var result7 = data.filter(function (verde) {return verde === 7});
            var result8 = data.filter(function (verde) {return verde === 8});
            var result9 = data.filter(function (verde) {return verde === 9});

            var nyadata = [result1.length, result2.length,
                           result3.length, result4.length,
                           result5.length, result6.length,
                           result7.length, result8.length,
                           result9.length];

            var nyarreymax = Math.max.apply(Math, nyadata);

            if (nyarreymax === result1.length){return 1;}
            if (nyarreymax === result2.length){return 2;}
            if (nyarreymax === result3.length){return 3;}
            if (nyarreymax === result4.length){return 4;}
            if (nyarreymax === result5.length){return 5;}
            if (nyarreymax === result6.length){return 6;}
            if (nyarreymax === result7.length){return 7;}
            if (nyarreymax === result8.length){return 8;}
            if (nyarreymax === result9.length){return 9;} 
            else { return  false;}

Hope you can help me to know code that works generally for strings and all integers.

回答1:

I'm a beginner at js myself and was looking for this same solution not long ago. Here's one I found that should be what you're looking for:

function findMode(arr) {
    var map = {};
    for (var i = 0; i < arr.length; i++) {
        if (map[arr[i]] === undefined) {
            map[arr[i]] = 0;
        }
        map[arr[i]] += 1;
    }
    var greatestFreq = 0;
    var mode;
    for (var prop in map) {
        if (map[prop] > greatestFreq) {
            greatestFreq = map[prop];
            mode = prop;
        }
    }
    return mode;
}

回答2:

You can try this using reduce() , see your console that shows value with counts.

Demo http://jsfiddle.net/ak69f/

var array_elements = ['Alex', 'Steven', 'Georg', 'Alice', 'Alex', 'Georg'];

var result = array_elements.reduce(function(p, c){
    if (c in p) {
       p[c]++;
    } else {
        p[c]=1;
    }
    return p;
}, []);

console.log(result);

回答3:

Here's a simple recursive solution, which seems to be the fastest of the four answers as you can see here: http://jsperf.com/array-mode.

var a = ["Alex", "Steven", "Georg", "Alice", "Alex", "Georg"];

function getMode(a, result) {
  result = result || {};
  
  if (a.length === 0){
    return result;
  }
  
  var head = a.shift();
  if (result[head]){
    result[head]++;
  }
  else{
    result[head] = 1;
  }
  return getMode(a, result);
}

console.log(getMode(a));

回答4:

First, define a new array that will hold your results. Iterate through your names array. Inside of each loop, iterate through the results array. If the current name in your names array exists within the results array, change the value.

For example, if your names array is on the second "Alex", and you iterate through the results array and find that "Alex:1" already exists, change the value to "Alex:2" (you will have to do a little bit of string parsing for that).

If the name does not exist already, add it to the end as ":1"

Then if you want to return the mode, you will have to write another loop that finds the maximum occurrence. Have a variable that keeps track of the array position of the name with the highest number (let's say it's called maxIndex). For each item in the array, compare it to the value of the array at maxIndex. If it's higher, reset maxIndex to the current index. If it's equal to or less than, move onto the next item of the array.

I know that was very wordy, so let me know if you have any questions.

回答5:

An alternative approach to this is to create a function that takes in your array, assigns each unique array value to an object property and if it already exists, increase the object properties value by one, like so;

function countArray(array){
        var results = {};

        for(var x = 0; x < array.length; x++){

            if(results[array[x]] == undefined){
                results[array[x]] = 1;
            }else{
                results[array[x]] += 1;
            }
        }

        return results;
    }

    var checkArray = countArray(['alex', 'george', 'steve', 'alex']);

    console.log(checkArray); 
    // outputs "Object {alex: 2, george: 1, steve: 1}"

Then you could access the results as needed by calling

console.log(checkArray.alex); // outputs 2

回答6:

var numbers = [1,2,2,3,4,5];
var counts = numbers.reduce((counts, e) => { counts[e] = counts[e] ? counts[e] + 1 : 1; return counts; }, {});
var mode = Object.keys(counts).reduce((a, b) => (counts[a] > counts[b] ? a : b ));
console.log(mode);

Reduce function can help a lot in aggregations.

来源：https://stackoverflow.com/questions/32786798/how-to-get-mode-in-array