dens rank of array

denseRank.ts

/**
 * denseRank({
 *   array: [
 *     {name: 'a', age: 20},
 *     {name: 'b', age: 5},
 *     {name: 'c', age: 20},
 *     {name: 'd', age: 75},
 *     {name: 'e', age: 21},
 *   ],
 *   column: 'age',
 *   ascOrDesc: 'asc'
 * })
 * => [
 *   {name: 'b', age: 5, rank: 1},
 *   {name: 'a', age: 20, rank: 2},
 *   {name: 'c', age: 20, rank: 2},
 *   {name: 'e', age: 21, rank: 3},
 *   {name: 'd', age: 75, rank: 4},
 * ]
 */
const denseRank = <T extends Record<string, unknown>>({
  records,
  column,
  ascOrDesc,
}: {
  records: T[]
  column: keyof T
  ascOrDesc: 'asc' | 'desc'
}): (T & { rank: number })[] => {
  const isAsc = ascOrDesc === 'asc'
  return Object.entries(
    // group by column
    records.reduce((acc: Record<string, T[]>, r) => {
      acc[r[column] as string] ??= []
      acc[r[column] as string].push(r)
      return acc
    }, {})
  )
    .sort(([a], [b]) => {
      return isAsc ? Number(a) - Number(b) : Number(b) - Number(a)
    })
    .map(([_, group], i) => {
      return group.map((r) => ({
        ...r,
        rank: i + 1,
      }))
    })
    .flat()
}