Is there a better way to do partial sums of array items in JavaScript?

Question

I wonder if there is a better way of generating a better performing solution for partial sums of an array.

Given an array say x = [ 0, 1, 2, 3, 4, 5 ], I generated sub-arrays of the items, and then computed the sum of each array which gives:

[ 0, 1, 3, 6, 10, 15 ] 

So the full code is:

x.map((y,i)=>x.filter((t,j)=>j<=i))  .map(ii=>ii.reduce((x,y)=>x+y,0)) 

I wonder if flat map or some other array method will have a solution that does not require expanding each subarray.

Answer 1

Much, by keeping a running total:

function* partialSums(iterable) {      let s = 0;        for (const x of iterable) {          s += x;          yield s;      }  }    const x = [0, 1, 2, 3, 4, 5];  console.log(Array.from(partialSums(x)).join(', '));

Linear time, online. (You can also produce an array directly; expand below.)

const partialSums = arr => {      let s = 0;      return arr.map(x => s += x);  };    const x = [0, 1, 2, 3, 4, 5];  console.log(partialSums(x).join(', '));