【Q679】实现一个函数 groupBy

[shfshanyue]

类似 lodash.groupBy

groupBy([
  { id: 1, name: '山月', sex: 'male' },
  { id: 2, name: '张三', sex: 'female' },
  { id: 3, name: '李四', sex: 'female' }
], x => x.sex)

[shfshanyue]

function groupBy (collection, by) {
  return collection.reduce((acc, x) => {
    if (acc[by(x)]) { acc[by(x)].push(x)}
    else { acc[by(x)] = [x] }
    return acc 
  }, {})
}

[heretic-G]

function groupBy (data, filter) {
    const map = {}
    data.forEach(curr => {
        const key = filter(curr)
        if (!map[key]) map[key] = []
        map[key].push(curr)
    })
    return map
}

[JoeWrights]

function groupBy(arr = [], callback) {
  const obj = {}
  const keys = arr.map(callback)
  keys.forEach(key => {
    obj[key] = []
  })

  arr.forEach(ele => {
    obj[callback(ele)].push(ele)
  })

  return obj
}