_.uniqBy(array, [iteratee=_.identity])

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_.uniqBy(array, [iteratee=_.identity])

_.uniqBy類似uniq方法，區別是需要傳入一個iteratee方法，用來處理每一個元素之后再比較

參數

[arrays] (...Array): 需要去重的數組

[iteratee=_.identity] (Function): 處理每一個元素的迭代器

返回值

(Array): 返回去重后的新數組

例子

_.uniqBy([2.1, 1.2, 2.3], Math.floor);
// => [2.1, 1.2]
 
// The `_.property` iteratee shorthand.
_.uniqBy([{ 'x': 1 }, { 'x': 2 }, { 'x': 1 }], 'x');
// => [{ 'x': 1 }, { 'x': 2 }]

源代碼：

iteratee參數也可以直接傳遞對象的屬性key，這樣的iteratee參數會被處理成一個函數，之前看過了，省略

import baseUniq from './.internal/baseUniq.js'

/**
 * This method is like `uniq` except that it accepts `iteratee` which is
 * invoked for each element in `array` to generate the criterion by which
 * uniqueness is computed. The order of result values is determined by the
 * order they occur in the array. The iteratee is invoked with one argument:
 * (value).
 *
 * @since 4.0.0
 * @category Array
 * @param {Array} array The array to inspect.
 * @param {Function} iteratee The iteratee invoked per element.
 * @returns {Array} Returns the new duplicate free array.
 * @see uniq, uniqWith
 * @example
 *
 * uniqBy([2.1, 1.2, 2.3], Math.floor)
 * // => [2.1, 1.2]
 */
//類似uniq方法，區別是需要傳入一個iteratee方法，用來處理每一個元素之后再比較
function uniqBy(array, iteratee) {
  return (array != null && array.length)
    ? baseUniq(array, iteratee)
    : []
    //如果數組不為空並且數組有長度，調用baseUniq處理，否則返回空數組
}

export default uniqBy

baseUniq

import SetCache from './SetCache.js'
import arrayIncludes from './arrayIncludes.js'//判斷數組是否包含給定值
import arrayIncludesWith from './arrayIncludesWith.js'//判斷數組是否包含給定值，區別是它的comparator需要作為參數傳入
import cacheHas from './cacheHas.js'
import createSet from './createSet.js'
import setToArray from './setToArray.js'

/** Used as the size to enable large array optimizations. */
const LARGE_ARRAY_SIZE = 200

/**
 * The base implementation of `uniqBy`.
 *
 * @private
 * @param {Array} array The array to inspect.
 * @param {Function} [iteratee] The iteratee invoked per element.
 * @param {Function} [comparator] The comparator invoked per element.
 * @returns {Array} Returns the new duplicate free array.
 */
//uniqBy的基礎實現，數組去重
function baseUniq(array, iteratee, comparator) {
  let index = -1//循環索引
  let includes = arrayIncludes//類似數組的includes方法，判斷數組是否包含給定值
  let isCommon = true//有沒有自定義比較器或者有沒有開啟緩存的標記

  const { length } = array//數組長度
  const result = []//結果數組
  let seen = result//臨時數組，用來存入不重復的數組元素值

  if (comparator) {//如果傳遞了自定義比較器，incledes方法就用arrayIncludesWith
    isCommon = false
    includes = arrayIncludesWith
  }
  else if (length >= LARGE_ARRAY_SIZE) {//如果數組長度超過200，就設置緩存
    const set = iteratee ? null : createSet(array)//如果沒有iteratee和comparator，就直接使用ES6的set類型去重
    if (set) {//如果可以用set類型去重，直接新建set對象然后再轉換成數組后返回結果
      return setToArray(set)
    }
    isCommon = false//否則開啟數組緩存
    includes = cacheHas
    seen = new SetCache
  }
  else {//如果沒有自定義比較器，數組長度也沒有超過200
    seen = iteratee ? [] : result
  }
  outer:
  while (++index < length) {//遍歷數組
    let value = array[index]//當前元素
    const computed = iteratee ? iteratee(value) : value//iteratee處理后的當前元素

    value = (comparator || value !== 0) ? value : 0//如果沒有傳遞comparator，將-0變為0
    if (isCommon && computed === computed) {//如果沒有傳遞自定義比較器，或者沒有開啟緩存，並且computed不是NaN
      let seenIndex = seen.length//seen數組的長度
      while (seenIndex--) {//遍歷seen數組，如果有和當前值一樣的，就跳出本次循環直接進行下一次
        if (seen[seenIndex] === computed) {
          continue outer
        }
      }
      if (iteratee) {//如果有iteratee參數，seen結尾插入當前不重復的元素
        seen.push(computed)
      }
      result.push(value)//結果數組結尾插入當前不重復的元素
    }
    else if (!includes(seen, computed, comparator)) {//如果有自定義比較器或者開啟了緩存，並且seen中沒有當前元素
      if (seen !== result) {//開啟緩存的情況seen數組要插入新值
        seen.push(computed)
      }
      result.push(value)//結果數組插入新值
    }
  }
  return result
}

export default baseUniq