_.unionBy([arrays], [iteratee=_.identity])


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_.unionBy([arrays], [iteratee=_.identity])
_.unionBy類似union方法,區別是傳遞一個iteratee方法來處理每一個數組元素來生成標准

參數

[arrays] (...Array): 需要處理的多個數組

[iteratee=_.identity] (Function): 處理每一個元素的遍歷器

返回值

(Array): 返回連起來的去重后的數組

例子

_.unionBy([2.1], [1.2, 2.3], Math.floor);
// => [2.1, 1.2]
 
// The `_.property` iteratee shorthand.
_.unionBy([{ '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,會被baseIteratee處理,省略

import baseFlatten from './.internal/baseFlatten.js'
import baseUniq from './.internal/baseUniq.js'
import isArrayLikeObject from './isArrayLikeObject.js'
import last from './last.js'

/**
 * This method is like `union` except that it accepts `iteratee` which is
 * invoked for each element of each `arrays` to generate the criterion by
 * which uniqueness is computed. Result values are chosen from the first
 * array in which the value occurs. The iteratee is invoked with one argument:
 * (value).
 *
 * @since 4.0.0
 * @category Array
 * @param {...Array} [arrays] The arrays to inspect.
 * @param {Function} iteratee The iteratee invoked per element.
 * @returns {Array} Returns the new array of combined values.
 * @see difference, union, unionWith, without, xor, xorBy
 * @example
 *
 * unionBy([2.1], [1.2, 2.3], Math.floor)
 * // => [2.1, 1.2]
 */
//類似union方法,區別是傳遞一個iteratee方法來處理每一個數組元素來生成標准
function unionBy(...arrays) {
  let iteratee = last(arrays)//最后一個元素是iteratee
  if (isArrayLikeObject(iteratee)) {//如果iteratee參數是array-like對象,就賦值為undefined
    iteratee = undefined
  }
  return baseUniq(baseFlatten(arrays, 1, isArrayLikeObject, true), iteratee)
  //調用baseUniq處理
}

export default unionBy
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

 


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