Group an array by primitive values or objects
npm install group-by-objectGroup an array by primitive values or objects using Maps.
``js`
npm install group-by-object
`js
import groupBy from 'group-by-object'
const array = [
{ a: 1, b: { c: 1, d: 4 } },
{ a: 2, b: { c: 1, d: 4 } },
{ a: 1, b: { c: 2, d: 4 } },
{ a: 1, b: { c: 1, d: 6 } }
]
const groups = groupBy(
array,
(item, index) => ({ // key selector
a: item.a,
c: item.b.c
}),
(item, index) => item // optional element selector
)
console.log(groups)
/*
Map {
{ a: 1, c: 1 } => [
{ a: 1, b: { c: 1, d: 4 } },
{ a: 1, b: { c: 1, d: 6 } }
],
{ a: 2, c: 1 } => [
{ a: 2, b: { c: 1, d: 4 } }
],
{ a: 1, c: 2 } => [
{ a: 1, b: { c: 2, d: 4 } }
]
}
*/
`
If you prefer a more fluent approach, you can automatically add the groupBy function to Array.prototype by doing the following:
`js
import groupBy from 'group-by-object'
groupBy.install()
...
const groups = array.groupBy(
item => ({
a: item.a,
c: item.b.c
})
) // returns a Map
`
Since this will still return a Map like the previous method, you can instead do groupBy.install(true) which will make Array.prototype.groupBy automatically convert the result to an array using Array.from internally.
So you can, for example, do:
`js
import groupBy from 'group-by-object'
groupBy.install(true)
...
const counted = array
.groupBy(
item => ({
a: item.a,
c: item.b.c
})
)
.map(([key, items]) => [key, items.length])
``