Map function to build an array from filtered object-CodePudding

I'm trying to get my head around map functions currently without much success.

I currently have a list of objects and am trying to remap to a new object using the map function to return a map indexed by the created property with a list of wooids.

Having written my map function, I only seem to be returning the last time.

const variants = [
{
   created: '2022-03-06',
    hashname: 'c78ba80402290724609a5e98c369c90984494152',
    hashobject: '80864e6329d5e305a512ace872ad7d56a3f41095',
    hashparent: '19c5d50ddddeb7c9a92469df78c47d9d611f1599',
    action: 'added',
    wooid: 7288
  },
{
   created: '2022-03-06',
    hashname: 'c78ba80402290724609a5e98c369c90984494152',
    hashobject: '80864e6329d5e305a512ace872ad7d56a3f41095',
    hashparent: '19c5d50ddddeb7c9a92469df78c47d9d611f1599',
    action: 'added',
    wooid: 7289
  }   
]

const res = Object.fromEntries(variants.map(k => [k.created, [k.wooid]]))
console.log(res)

Current output

{ '2022-03-06': [ 7289 ] }

Desired output:

{ '2022-03-06': [ 7289, 7288 ] }

Any help would be greatly appreciated as I'm unsure how to dynamically populate the array to include all other entires (6 in total).

CodePudding user response：

Use Array.prototype.reduce() to build up your object. Check if you already have a key for each created value and if not, create an empty array. Then append the wooid value

const variants = [{"created":"2022-03-06","hashname":"c78ba80402290724609a5e98c369c90984494152","hashobject":"80864e6329d5e305a512ace872ad7d56a3f41095","hashparent":"19c5d50ddddeb7c9a92469df78c47d9d611f1599","action":"added","wooid":7288},{"created":"2022-03-06","hashname":"c78ba80402290724609a5e98c369c90984494152","hashobject":"80864e6329d5e305a512ace872ad7d56a3f41095","hashparent":"19c5d50ddddeb7c9a92469df78c47d9d611f1599","action":"added","wooid":7289}]

const res = variants.reduce((acc, { created, wooid }) => ({
  ...acc,
  [ created ]: [
    ...acc[created] ?? [], // init to an empty array if unset
    wooid
  ]
}), {})

console.log(res)

This will collect wooid values by created in the order they appear in the original data.