Edit multiple value in object based on array

Question

Suppose I have:

const fixed = {pear: 100, apple: 4}
const arr = [
  {name: 'P1', pear: 150, apple: 2},
  {name: 'P2', pear: 50, apple: 5},
  {name: 'P3', pear: 450, apple: 1},
  {name: 'P4', pear: 100, apple: 3},
]

and I want to have:

const result = [
  {name: 'P1', pear: -50, apple: 2},
  {name: 'P2', pear: 50, apple: -1},
  {name: 'P3', pear: -350, apple: 3},
  {name: 'P4', pear: 0, apple: 1},
]

So result has the same items of arr but with edited apple and pear values based on fixed object values.

The new pear (and apple) value should be fixed.pear - oldPearValue, so for example, for arr[0]:

fixed.pear - arr[0].pear = 100 - 150 = -50 --> result[0].pear = -50

Here is what I tried:

function difference(fixed, value) {
  return value - fixed
}

const fixed = {pear: 100, apple: 4}
const arr = [
  {name: 'P1', pear: 150, apple: 2},
  {name: 'P2', pear: 50, apple: 5},
  {name: 'P3', pear: 450, apple: 1},
  {name: 'P4', pear: 100, apple: 3},
]

const dataset = arr.flatMap((d) => {
  Object.entries(fixed).forEach(([key, value]) => {
    return { ...d, [key]: difference(value, d[key]) }
  })
})

console.log(dataset)

as you can see, the result is [ undefined, undefined, undefined, undefined ]..

Because the callback of the unnecessary .flatMap() call doesn't return anything — Andreas
– Andreas, Commented Sep 21, 2020 at 11:02
.return ... in a .forEach() callback doesn't do anything. — Andreas
– Andreas, Commented Sep 21, 2020 at 11:03

Nina Scholz · Accepted Answer · 2020-09-21 11:05:26Z

2

You could get the entries and map new properties.

const
    fixed = { pear: 100, apple: 4 },
    arr = [{ name: 'P1', pear: 150, apple: 2 }, { name: 'P2', pear: 50, apple: 5 }, { name: 'P3', pear: 450, apple: 1 }, { name: 'P4', pear: 100, apple: 3 }],
    dataset = arr.map(d => ({ ...d, ...Object.fromEntries(Object
      .entries(fixed)
      .map(([k, v]) => [k, v - d[k]])
  ) }));

console.log(dataset);

.as-console-wrapper { max-height: 100% !important; top: 0; }

answered Sep 21, 2020 at 11:05

Nina Scholz

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Comments

Ahmad Suddle · Accepted Answer · 2020-09-21 11:13:06Z

0

If the fixed object has to be a fixed object with same fields, then you can try this

        const fixed = { pear: 100, apple: 4 };
        const arr = [
            { name: 'P1', pear: 150, apple: 2 },
            { name: 'P2', pear: 50, apple: 5 },
            { name: 'P3', pear: 450, apple: 1 },
            { name: 'P4', pear: 100, apple: 3 }
        ];

        let data = arr.map((item) => {
            return { ...item, pear: fixed.pear - item.pear,     apple: fixed.apple - item.apple };
        });
        console.log('checkk', data);

answered Sep 21, 2020 at 11:13

Ahmad Suddle

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