Convert array of objects into subarrays of objects by a selected property (javascript)-CodePudding

I am looking to take an array of objects, and convert it into an array of subarrays based on a chosen object property

for example:

[
  {foo: 1, bar: a}, {foo: 2, bar: b}, {foo: 1, bar: c}, {foo: 2, bar: d}
]

Create subarrays with the foo property would become:

[
  [
    {foo: 1, bar: a}, {foo: 1, bar: c}, 
  ],
  [
    {foo: 2, bar: b}, {foo: 2, bar: d}
  ]
]

I can't think of an efficient way to this. I keep resorting to creating a set of all of the unique property values of my chosen value, and then brute forcing through it multiple times.

const distinctProperties =  [...new Set(originalArray.map(item => item.foo))]

const newArray = distinctProperties.map(item => originalArray.filter(obj => obj.foo === item))

Thanks in advance for some advice here!

CodePudding user response：

can be done with reduce. you can wrap this around another function to group by the key you want.

Here I'm grouping based on the value of foo and res will be like this

{
  1: [{
  bar: "a",
  foo: 1
}, {
  bar: "c",
  foo: 1
}],
  2: [{
  bar: "b",
  foo: 2
}, {
  bar: "d",
  foo: 2
}]
}

then I'm taking Object.values of this to get the array format you want

let a =[
  {foo: 1, bar: 'a'}, {foo: 2, bar: 'b'}, {foo: 1, bar: 'c'}, {foo: 2, bar: 'd'}
]

let res= Object.values(a.reduce((acc,curr)=> {
    if(!acc[curr.foo])acc[curr.foo]=[];
  acc[curr.foo].push(curr)
    return acc;
},{}))

console.log(res)

As a generalized function to take key name as input

let a =[
  {foo: 1, bar: 'a'}, {foo: 2, bar: 'b'}, {foo: 1, bar: 'c'}, {foo: 2, bar: 'd'}
]


let groupByValue = (arr,key) => {
    return Object.values(arr.reduce((acc,curr)=> {
    if(!acc[curr[key]])acc[curr[key]]=[];
  acc[curr[key]].push(curr)
    return acc;
},{}))
}

let res1 = groupByValue(a,'foo')
let res2 = groupByValue(a,'bar')
console.log(res1)
console.log(res2)