使用 discardWith() 自訂條件移除 Array 中 Element | 點燈坊

discard() 若要也能有 discardWith()，其中一個方法就是借用 withoutWith() 組合而成。

Version

macOS Catalina 10.15.6
Wink-fp 1.23.7

Functional

import { eqProps, of } from 'ramda'
import { withoutWith } from 'wink-fp'

let data = [
  { title: 'FP in JavaScript', price: 100 },
  { title: 'RxJS in Action', price: 200 },
  { title: 'Speaking JavaScript', price: 300 }
]

let obj = { title: 'FP in JavaScript', price: 100 }

// discardWith :: ((a, a) -> Boolean) -> a -> [a] -> [a]
let discardWith = pred => v => a => {
  let arr = of(v)
  return withoutWith(pred, arr, a)
}

discardWith((x, y) => x.title === y.title)(obj)(data) // ?

12 行

// discardWith :: ((a, a) -> Boolean) -> a -> [a] -> [a]
let discardWith = pred => v => a => {
  let arr = of(v)
  return withoutWith(pred, arr, a)
}

discardWith() 與 withoutWith() 差異只在於一個是傳 value，一個是傳 Array。

• 使用 of() 將 value 轉成 Array
• 再使用 withoutWith() 移除 element

Point-free

import { eqProps, of, useWith, identity } from 'ramda'
import { withoutWith } from 'wink-fp'

let data = [
  { title: 'FP in JavaScript', price: 100 },
  { title: 'RxJS in Action', price: 200 },
  { title: 'Speaking JavaScript', price: 300 }
]

let obj = { title: 'FP in JavaScript', price: 100 }

// discardWith :: ((a, a) -> Boolean) -> a -> [a] -> [a]
let discardWith = useWith(
  withoutWith, [identity, of, identity]
)

discardWith(eqProps('title'), obj, data) // ?

12 行

// discardWith :: ((a, a) -> Boolean) -> a -> [a] -> [a]
let discardWith = useWith(
  withoutWith, [identity, of, identity]
)

使用 useWith() 使 discardWith() 能 point-free。

Wink-fp

import { eqProps } from 'ramda'
import { discardWith } from 'wink-fp'

let data = [
  { title: 'FP in JavaScript', price: 100 },
  { title: 'RxJS in Action', price: 200 },
  { title: 'Speaking JavaScript', price: 300 }
]

let obj = { title: 'FP in JavaScript', price: 100 }

discardWith(eqProps('title'), obj, data) // ?

Wink-fp 已經內建 discardWith() 可直接使用。

discardWith()
((a, a) -> Boolean) -> a -> [a] -> [a]
提供自訂條件移除 Array 中 Element

Conclusion

• 帶有 with() 的 function 對於 Object 特別重要，我們可藉此指定只比對 Object 特定 property 比較即可