JS: Group by 2 keys

Question

I have like to group an array of objects.

var _ = require('lodash')

const objects = [
  { a: 'test1', b: 'sample', c: 'ten' },
  { a: 'test2', b: 'sample', c: 'ten' },
  { a: 'test3', b: 'sampleone', c: 'ten' },
  { a: 'test4', b: 'sample', c: 'tentwo' },
]

//using lodash, groupBy b and c and concat 'a' values
const grouped = _(objects)
  .groupBy('b', 'c')
  .map((value, key) => ({
    b: key,
    c: value[0].c,
    a: _.map(value, 'a').join('|'),
  }))
  .value()

console.log(grouped)

The output from above is:

[
  { b: 'sample', c: 'ten', a: 'test1|test2|test4' },
  { b: 'sampleone', c: 'ten', a: 'test3' }
]

But I have like the output to be below, only group by b is 'sample' and c is 'ten'

[
  { b: 'sample', c: 'ten', a: 'test1|test2' },
  { b: 'sampleone', c: 'ten', a: 'test3' },
  { b: 'sample', c: 'tentwo', a: 'test4' }
]

Any help would be greatly appreciated.

Answer 1

To group by multiple keys you will to need do something like

.groupBy(({b,c}) => `${b}|${c}`)

i.e joining the individual keys and creating a new composite key (also will have create it in such a way that it becomes unique)

now the grouped object will look like this before the map call

{
  sampleone|ten: [{
  a: "test3",
  b: "sampleone",
  c: "ten"
}],
  sample|ten: [{
  a: "test1",
  b: "sample",
  c: "ten"
}, {
  a: "test2",
  b: "sample",
  c: "ten"
}],
  sample|tentwo: [{
  a: "test4",
  b: "sample",
  c: "tentwo"
}]
}

const objects = [
  { a: 'test1', b: 'sample', c: 'ten' },
  { a: 'test2', b: 'sample', c: 'ten' },
  { a: 'test3', b: 'sampleone', c: 'ten' },
  { a: 'test4', b: 'sample', c: 'tentwo' },
]


const grouped = _(objects)
  .groupBy(({b,c}) => `${b}|${c}`)
  .map((value, key) => ({
    b: value[0].b,
    c: value[0].c,
    a: _.map(value, 'a').join('|'),
  }))
  .value()

console.log(grouped)

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