Finding difference between consecutive numbers in an array in javascript

Question

I have the following array

A=[1,2,3,3,0] 

and if I want to calculate difference between consecutive numbers in an array. I could do it in Matlab with using built-in function (diff)

B=diff(A) returns

B = [1,1,0,-3]

I would like to know there is any similar built-in function in javascript?

Answer 1

If you prefer functional programming, here's a solution using map:

function diff(A) {
  return A.slice(1).map(function(n, i) { return n - A[i]; });
}

A little explanation: slice(1) gets all but the first element. map returns a new value for each of those, and the value returned is the difference between the element and the corresponding element in A, (the un-sliced array), so A[i] is the element before [i] in the slice.

Here is the jsfiddle : https://jsfiddle.net/ewbmrjyr/2/

Answer 2

There's no such built-in function, but writing one is simple:

function diff(ary) {
    var newA = [];
    for (var i = 1; i < ary.length; i++)  newA.push(ary[i] - ary[i - 1])
    return newA;
}
var A = [1, 2, 3, 3, 0];
console.log(diff(A)) // [1, 1, 0, -3]

here is the fiddle: https://jsfiddle.net/ewbmrjyr/1/