i have a problem with reduce.
I want to add the rest of the arrays from the first array in the array. array = [[a,b],[c,d],[e,f]] the order to come is: (a-b)+(c-d)+(e-f), but my code not work :((
my code is:
const sumAndSubtract = (numberInNestedArray) => {
return numberInNestedArray.reduce((acc, cur, ind, arr) => {
const firstSubtract = arr[0][0] - arr[0][1];
const otherSubtract = acc[ind] - cur[ind];
console.log(firstSubtract);
console.log(otherSubtract);
return firstSubtract + otherSubtract;
})
}
console.log(sumAndSubtract([
[10, 0],
[5, 7],
[6, 9]
]))expect result: 10 + (-2)+(-3)
Use reduce as follows, where a is the accumulating sum, and b and c are the atomic values retrieved from each pair:
let result = [[10, 0], [5, 7], [6, 9]].reduce((a, [b, c]) => a+b-c, 0);
console.log(result);In your attempt, the following is not right:
The expression arr[0][0] - arr[0][1]. This only looks at the first pair in the array, and does so in each iteration. Instead, you should be doing cur[0] - cur[1].
The expression acc[ind] - cur[ind]: ind is the index in the outer array, which takes values 0, 1 and 2 for the example input. acc[ind] is a pair, not a number and cur[ind] will at some point be an out of range reference, as cur only has two values.
The call to reduce should get the initial value argument, because without it, the first pair will be the initial value of acc, which you don't want: you want a number. So pass 0 as initial value argument to reduce.
What you call otherSubtract is already given as acc, so you actually don't need this variable.
You could map the subtractions and add the values later.
const
add = (a, b) => a + b,
subtract = (a, b) => a - b,
sumAndSubtract = array => array
.map(a => a.reduce(subtract))
.reduce(add);
console.log(sumAndSubtract([[10, 0], [5, 7], [6, 9]]));The shortest way to do it will be:
numberInNestedArray.reduce((acc, cur) => acc + (cur[0] - cur[1]), 0)