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?
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/
const diff = (A) => { return A.slice(1).map( (item,index) => { return item - A[index] } )}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/
The code can by simplified by using Array methods and Arrow functions:
var visitsArr = [38,29,18,29,28,18,24];
var diffs = visitsArr.slice(1).map((x,i)=> x-visitsArr[i]);
diffs.forEach((x,i) => console.log(
`Visits from day ${i+1} to day ${i+2} increased by ${x}`
));For more information, see
var a = [1,2,3,3,0] ;
function diff (arr){
diffArr=[];
for(var i=0; i<arr.length-1; i++){
diffArr.push(arr[i+1]-arr[i]);
}
return diffArr;
}
alert(diff(a)); //[1,1,0,-3]
