如何计算给定数字以下/上方的数组中的元素数（javascript）

Question

It's example of array which contains only numbers:

var array = [3.1, 1, 2.2, 5.1, 6, 7.3, 2.1, 9]

EDITED

How to count how many(edited from word 'sum') of elements are in array below / above given number eg. '5.25'?

So answer should be 5 elements are below (3.1, 1, 2.2, 5.1, 2.1) and 3 element are above (6, 7.3, 9)

Answer 1

Use Array#reduce with an object { above: 0, below: 0 } as initial value. On each iteration check each number against the media, and accordingly add 1 to above/below.

Note: This is an array of strings. I've converted them manually to numbers. I also assume that a number that equals the median should be added to below. If you want to skip this numbers, change the comparison to < .

 var array = [3.1, 1, 2.2, 5.1, 6, 7.3, 2.1, 9]; var median = 5.25; var counts = array.reduce(function(s, n) { s[n <= median ? 'below' : 'above'] += 1; return s; }, { above: 0, below: 0 }); console.log(counts); 

If you must have an array of strings, you can convert to a number in run time using String#parseFloat or the + operator :

 var array = ['3.1', '1', '2.2', '5.1', '6', '7.3', '2.1', '9']; var median = 5.25; var counts = array.reduce(function(s, str) { s[+str <= median ? 'below' : 'above'] += 1; return s; }, { above: 0, below: 0 }); console.log(counts); 

Answer 2

No need for reduce, because the result does not change by using reduce, it is still an object.

 var array = [3.1, 1, 2.2, 5.1, 6, 7.3, 2.1, 9], value = 5.25, counts = { below: 0, equal: 0, above: 0 }; array.forEach(function(v) { counts[{ '-1': 'below', 0: 'equal', 1: 'above' }[Math.sign(v - value)]]++; }); console.log(counts); 

Answer 3

Assuming you are using an array of numbers..

I use lodash ...it helps shorten the code &

 var array = [3.1, 1, 2.2, 5.1, 6, 7.3, 2.1, 9]; console.log(_.sum(array)); // _.sum does the addition 

 <script src="https://cdn.jsdelivr.net/lodash/4.14.1/lodash.min.js"></script> 

Answer 4

There are couple of strategies but I will use the one thats easy to read and understand:

(1) Create a new array with all elements that fit the criteria aka <=5.25

let sampleArr = ['3.1', '1', '2.2', '5.1', '6', '7.3', '2.1', '9'];

let sortedArr = sampleArr.filter(function(e){
     return parseInt(e) <= 5.25
});

Notice I wrote parseInt(e), that converts the string into a number. The values you gave in your array were all strings.

(2) Now simply get the length of the sortedArr like so:

let finalCount = sortedArr.length;

Hope this helps!