mapping one object to another using some functional programming

Question

I would like to map one array of object into another in a more functional style, I am using typescript.

Basically I am using delete to remove a property on a object, I would like to know if there is a better way to write it.

  const data = props.data.map(d => ({
    order: d.position,
    logs: d.batches.map(b => {
      let log= {
        amount: b.scrap,
        batchNumber: '', // NO GOOD
      }
      if (!b.batch || b.batch.length === 0) {
        delete log.batchNumber // NO GOOD
      }
      return log
    }),
  }))

example input data:

const data = [
    position: 1,
    batches: [
         {batchNumber: '', ammount: 3}
    ]
]

result:

const data = [{
        order: 1,
        logs:[ {ammount:3}]
    }
]

Can you give an example of your input/output data?

Andy
– Andy

2018-01-31 11:43:19 +00:00
Commented Jan 31, 2018 at 11:43 — Andy
– Andy, Commented Jan 31, 2018 at 11:43

Andy · Accepted Answer · 2018-01-31 12:05:19Z

2

You can do another map on the batches to return a new array of objects, and attach that to your returned object instead:

const out = data.map(({ position: order, batches }) => {
  const logs = batches.map(({ batchNumber, ammount }) => {
    if (batchNumber) return { batchNumber, ammount };
    return { ammount };
  });
  return { order, logs }
});

DEMO

edited Jan 31, 2018 at 12:05

answered Jan 31, 2018 at 11:53

Andy

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2 Comments

Radex Over a year ago

I need to add batchNumber if its property exist and its value is different than an empty string, does you code work in this way?

Andy Over a year ago

It does now @Radex.

georg · Accepted Answer · 2018-01-31 11:48:02Z

1

One approach would be to make a shallow copy of the target omitting keys you want to delete, for example:

let drop = key => obj => Object.keys(obj).reduce((r, k) =>
    k === key ? r : {...r, [k]: obj[k]}, {});

let test = [
    {foo:11, bar:2, baz: 3},
    {foo:22, bar:2, baz: 3},
    {foo:33, bar:2, baz: 3},
    ];

console.log(test.map(drop('bar')));

answered Jan 31, 2018 at 11:48

georg

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Comments

Me.Name · Accepted Answer · 2018-01-31 12:37:29Z

1

To add another option to the mix: it is possible to use Object.assign to optionally assign the property:

const data = [{
  position: 1,
  batches: [{batchNumber: '',ammount: 3}, {batchNumber: 'withNr',ammount: 4}]
}];
 
const res = data.map(d => 
  ({
    order: d.position,
    logs : d.batches.map(({ammount, batchNumber}) => Object.assign({ammount}, batchNumber ? {batchNumber} : null ))
  })
);
 
 console.log(res);

answered Jan 31, 2018 at 12:37

Me.Name

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