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

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

_.uniqBy类似uniq方法，区别是需要传入一个iteratee方法，用来处理每一个元素之后再比较

参数

[arrays] (...Array): 需要去重的数组

[iteratee=_.identity] (Function): 处理每一个元素的迭代器

返回值

(Array): 返回去重后的新数组

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 }]

源代码：

iteratee参数也可以直接传递对象的属性key，这样的iteratee参数会被处理成一个函数，之前看过了，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]
 */
//类似uniq方法，区别是需要传入一个iteratee方法，用来处理每一个元素之后再比较
function uniqBy(array, iteratee) {
  return (array != null && array.length)
    ? baseUniq(array, iteratee)
    : []
    //如果数组不为空并且数组有长度，调用baseUniq处理，否则返回空数组
}

export default uniqBy

baseUniq

import SetCache from './SetCache.js'
import arrayIncludes from './arrayIncludes.js'//判断数组是否包含给定值
import arrayIncludesWith from './arrayIncludesWith.js'//判断数组是否包含给定值，区别是它的comparator需要作为参数传入
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的基础实现，数组去重
function baseUniq(array, iteratee, comparator) {
  let index = -1//循环索引
  let includes = arrayIncludes//类似数组的includes方法，判断数组是否包含给定值
  let isCommon = true//有没有自定义比较器或者有没有开启缓存的标记

  const { length } = array//数组长度
  const result = []//结果数组
  let seen = result//临时数组，用来存入不重复的数组元素值

  if (comparator) {//如果传递了自定义比较器，incledes方法就用arrayIncludesWith
    isCommon = false
    includes = arrayIncludesWith
  }
  else if (length >= LARGE_ARRAY_SIZE) {//如果数组长度超过200，就设置缓存
    const set = iteratee ? null : createSet(array)//如果没有iteratee和comparator，就直接使用ES6的set类型去重
    if (set) {//如果可以用set类型去重，直接新建set对象然后再转换成数组后返回结果
      return setToArray(set)
    }
    isCommon = false//否则开启数组缓存
    includes = cacheHas
    seen = new SetCache
  }
  else {//如果没有自定义比较器，数组长度也没有超过200
    seen = iteratee ? [] : result
  }
  outer:
  while (++index < length) {//遍历数组
    let value = array[index]//当前元素
    const computed = iteratee ? iteratee(value) : value//iteratee处理后的当前元素

    value = (comparator || value !== 0) ? value : 0//如果没有传递comparator，将-0变为0
    if (isCommon && computed === computed) {//如果没有传递自定义比较器，或者没有开启缓存，并且computed不是NaN
      let seenIndex = seen.length//seen数组的长度
      while (seenIndex--) {//遍历seen数组，如果有和当前值一样的，就跳出本次循环直接进行下一次
        if (seen[seenIndex] === computed) {
          continue outer
        }
      }
      if (iteratee) {//如果有iteratee参数，seen结尾插入当前不重复的元素
        seen.push(computed)
      }
      result.push(value)//结果数组结尾插入当前不重复的元素
    }
    else if (!includes(seen, computed, comparator)) {//如果有自定义比较器或者开启了缓存，并且seen中没有当前元素
      if (seen !== result) {//开启缓存的情况seen数组要插入新值
        seen.push(computed)
      }
      result.push(value)//结果数组插入新值
    }
  }
  return result
}

export default baseUniq