Useful JS Tips

#41 - Array average and median

2016-02-10 by @soyuka

The following examples will be based on the following array:

let values = [2, 56, 3, 41, 0, 4, 100, 23];

To get the average, we have to sum up numbers and then divide by the number of values. Steps are:

  • get the array length
  • sum up values
  • get the average (sum/length)
let values = [2, 56, 3, 41, 0, 4, 100, 23];
let sum = values.reduce((previous, current) => current += previous);
let avg = sum / values.length;
// avg = 28

Or:

let values = [2, 56, 3, 41, 0, 4, 100, 23];
let count = values.length;
values = values.reduce((previous, current) => current += previous);
values /= count;
// avg = 28

Now, to get the median steps are:

  • sort the array
  • get the arethmic mean of the middle values
let values = [2, 56, 3, 41, 0, 4, 100, 23];
values.sort((a, b) => a - b);
let lowMiddle = Math.floor((values.length - 1) / 2);
let highMiddle = Math.ceil((values.length - 1) / 2);
let median = (values[lowMiddle] + values[highMiddle]) / 2;
// median = 13,5

With a bitwise operator:

let values = [2, 56, 3, 41, 0, 4, 100, 23];
values.sort((a, b) => a - b);
let median = (values[(values.length - 1) >> 1] + values[values.length >> 1]) / 2
// median = 13,5
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