Create array of values from a dictionary of array of objects filtered by property

Question

I have a dictionary where key is string and value is array of objects:

objDict = {
  dataset1: [ { id: 1, count: 6 }, { id: 2, count: 7 }, { id: 3, count: 8 } ],
  dataset2: [ { id: 1, count: 5 }, { id: 2, count: 4 }, { id: 3, count: 3 } ]
}

I need to filter objects with specific id and create an array of count values: for id = 2 it would be countArray = [ 7, 4 ]. I suppose I should first use Object.values(objDict) but I don't know what to do afterwards.

Answer 1

Convert the object to an array with Object.values(), flatten to a single array, reduce and push the relevant count values to the accumulator (acc) array:

const getCountById = (id, dict) => Object.values(objDict)
  .flat()
  .reduce((acc, { id: oid, count }) => {
    if(id === oid) acc.push(count)
  
    return acc
  }, [])


const objDict = {
  dataset1: [ { id: 1, count: 6 }, { id: 2, count: 7 }, { id: 3, count: 8 } ],
  dataset2: [ { id: 1, count: 5 }, { id: 2, count: 4 }, { id: 3, count: 3 } ]
}

const result = getCountById(2, objDict)

console.log(result)

This is a bit of an abuse of reduce, the more idiomatic form would be to filter by the id, and then to map the objects to the count values:

const getCountById = (id, dict) => Object.values(objDict)
  .flat()
  .filter(o => o.id === id)
  .map(o => o.count)


const objDict = {
  dataset1: [ { id: 1, count: 6 }, { id: 2, count: 7 }, { id: 3, count: 8 } ],
  dataset2: [ { id: 1, count: 5 }, { id: 2, count: 4 }, { id: 3, count: 3 } ]
}

const result = getCountById(2, objDict)

console.log(result)