I need to calculate the sum of columns in an array with objects

Question

I have a two-dimensional array, the cells are an object {id, amount}, you need to add a sum of columns, while using only methods. What I did -

let matrix = [
    [{id:1, amount:11},{id:2, amount:22},{id:3, amount:33}],
    [{id:4, amount:44},{id:5, amount:55},{id:6, amount:66}],
    [{id:7, amount:77},{id:8, amount:88},{id:9, amount:99}],
    [{id:10, amount:100},{id:11, amount:111},{id:12, amount:112}],
];

let c = matrix.reduce((acc, cur)=> {
    return acc.map((item, index)=> {
        return item + cur[index].amount;
    })
});
console.log(c);

Yup, it's actually quite unclear! I think everyone didn't understand the same thing. — sjahan
– sjahan, Commented Jul 26, 2019 at 14:42
output value: ["[object Object]4477100", "[object Object]5588111", "[object Object]6699112"] but need: [232, 276, 310] — Женя Борісевіч
– Женя Борісевіч, Commented Jul 29, 2019 at 8:17

sjahan · Accepted Answer · 2019-07-29 14:41:48Z

2

Why not using flatMap then reduce?

let matrix = [
        [{id:1, amount:11},{id:2, amount:22},{id:3, amount:33}],
        [{id:4, amount:44},{id:5, amount:55},{id:6, amount:66}],
        [{id:7, amount:77},{id:8, amount:88},{id:9, amount:99}],
        [{id:10, amount:100},{id:11, amount:111},{id:12, amount:112}],
    ];
let result = matrix.flatMap(it => it).reduce((acc, item) => acc + item.amount, 0);
console.log(result)

EDIT

After getting what you actually wanted to do, here is a complement (feel free not to read above).

const matrix = [
        [{id:1, amount:11},{id:2, amount:22},{id:3, amount:33}],
        [{id:4, amount:44},{id:5, amount:55},{id:6, amount:66}],
        [{id:7, amount:77},{id:8, amount:88},{id:9, amount:99}],
        [{id:10, amount:100},{id:11, amount:111},{id:12, amount:112}],
    ];
    
let result = matrix
             .flatMap(it => it) //This flattens the items.
             .reduce((acc, item, i) => (acc[i%matrix[0].length] += item.amount, acc), //This computes the sum based on the indices and the matrix width.
             Array.apply(0, Array(matrix[0].length)).map(_ => 0)); //This inits the result array with zeros.

console.log(result)

edited Jul 29, 2019 at 14:41

answered Jul 26, 2019 at 14:40

sjahan

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2 Comments

Женя Борісевіч Over a year ago

I need an array of each column amount, example [232, 276, 310]

sjahan Over a year ago

@ЖеняБорісевіч another piece of code ;) You tell me if you like it!

Maheer Ali · Accepted Answer · 2019-07-26 14:41:41Z

0

You can create an array of length equal to width of array. Then use nested forEach to add the values to corresponding element.

let matrix = [
        [{id:1, amount:11},{id:2, amount:22},{id:3, amount:33}],
        [{id:4, amount:44},{id:5, amount:55},{id:6, amount:66}],
        [{id:7, amount:77},{id:8, amount:88},{id:9, amount:99}],
        [{id:10, amount:100},{id:11, amount:111},{id:12, amount:112}],
    ];

let res = Array(matrix[0].length).fill(0)
matrix.forEach(x => {
  x.forEach((y,i) => {
    res[i] += y.amount;
  })
})

console.log(res)

answered Jul 26, 2019 at 14:41

Maheer Ali

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1 Comment

Женя Борісевіч Over a year ago

possible without using for, foreach

Женя Борісевіч · Accepted Answer · 2019-07-29 09:23:16Z

0

So decided, if there are better solutions, I will be glad to see

getColSumMatrix = matrix =>
    matrix.reduce((acc, cur) =>
      acc.map((value, i) =>
        typeof value == "object"
          ? value.amount + cur[i].amount
          : value + cur[i].amount
      )
    );

answered Jul 29, 2019 at 9:23

Женя Борісевіч

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Comments

Lucas Charvolin · Accepted Answer · 2019-07-26 14:40:10Z

-1

const summ = matrix.reduce((acc, table) => {
        return (
            acc +
            table.reduce((acc, { amount }) => {
                return acc + amount;
            }, 0)
        );
    }, 0);

answered Jul 26, 2019 at 14:40

Lucas Charvolin

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1 Comment

Женя Борісевіч Over a year ago

I need an array of each column amount, example [232, 276, 310]

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