Copying subarrays into another array while changing them?

Question

So I'm trying to copy these subarrays into another array and change them so their values are cumulative as I put them in. In order to make them cumulative, I am using the map function and modeling that based on the constant variable I made. In my attempts to copy them over into the other array, I have tried concat, push, and other methods without success.

JS

const cumulative = (cumu => val => cumu += val)(0);
var series2 = series.map(cumulative);

            series: [
                [55, 65, 76, 88, 44, 33, 54, 65, 7, 98, 12, 109],
                [52, 25, 26, 82, 24, 23, 34, 65, 47, 59, 12, 19],
                [57, 68, 77, 78, 44, 43, 74, 16, 71, 91, 11, 29]
            ]

This array below is just to demonstrate the desired effect I am attempting to do...

series2: [
    [55, 120, 196... etc...],
    [...],
    [...]
]

The second array is just an example array, it is not created. — grahamfk45c
– grahamfk45c, Commented Dec 12, 2020 at 22:01
@PraveenKumarPurushothaman No, I do not get syntax errors. One attempt I tried ended up combining all three arrays into one and then pushing them into the second array, but that is not what I want. — grahamfk45c
– grahamfk45c, Commented Dec 12, 2020 at 22:02

Praveen Kumar Purushothaman · Accepted Answer · 2020-12-12 22:04:26Z

1

Guess I cracked it. Your logic is wrong there, you should use an inner map:

series = [
  [55, 65, 76, 88, 44, 33, 54, 65, 7, 98, 12, 109],
  [52, 25, 26, 82, 24, 23, 34, 65, 47, 59, 12, 19],
  [57, 68, 77, 78, 44, 43, 74, 16, 71, 91, 11, 29]
];
const cumulative = (cumu) => {
  var val = 0;
  return cumu.map(c => val += c);
};
var series2 = series.map(cumulative);
console.log(series2);

I get this as output and this is what you're upto:

[
  [55, 120, 196, 284, 328, 361, 415, 480, 487, 585, 597, 706],
  [758, 783, 809, 891, 915, 938, 972, 1037, 1084, 1143, 1155, 1174],
  [1231, 1299, 1376, 1454, 1498, 1541, 1615, 1631, 1702, 1793, 1804, 1833]
]

answered Dec 12, 2020 at 22:04

Praveen Kumar Purushothaman

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Comments

Robin Zigmond · Accepted Answer · 2020-12-12 22:05:54Z

1

I think reduce is the best tool to transform an array in the way you want - to one of cumulative sums. Use this to define the function that transforms a single array, then just map it over the outer array:

const series = [
    [55, 65, 76, 88, 44, 33, 54, 65, 7, 98, 12, 109],
    [52, 25, 26, 82, 24, 23, 34, 65, 47, 59, 12, 19],
    [57, 68, 77, 78, 44, 43, 74, 16, 71, 91, 11, 29]
];

const makeCumulative = arr => arr.reduce((cums, current) => {
  const subtotal = cums[cums.length - 1] || 0;
  return [...cums, subtotal + current];
}, []);

const series2 = series.map(makeCumulative);

console.log(series2);

answered Dec 12, 2020 at 22:05

Robin Zigmond

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Comments

Alberto · Accepted Answer · 2020-12-12 22:07:06Z

1

Using reduce:

let series = [
    [55, 65, 76, 88, 44, 33, 54, 65, 7, 98, 12, 109],
    [52, 25, 26, 82, 24, 23, 34, 65, 47, 59, 12, 19],
    [57, 68, 77, 78, 44, 43, 74, 16, 71, 91, 11, 29],
];
console.log(series.map(
    (ar) => ar.reduce((acc, el) => [...acc, el + (acc[acc.length - 1] || 0)], [])
));

answered Dec 12, 2020 at 22:07

Alberto

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