select

根据条件过滤和转换数组元素。

语法

select<T, R>(
  array: T[],
  transform: (item: T) => R,
  condition?: (item: T) => boolean
): R[]

参数

• array (T[]): 要处理的数组
• transform ((item: T) => R): 转换函数
• condition ((item: T) => boolean, 可选): 过滤条件

返回值

• R[]: 过滤和转换后的数组

示例

基本用法

import { select } from 'radash'

const users = [
  { name: 'Alice', age: 25 },
  { name: 'Bob', age: 30 },
  { name: 'Charlie', age: 35 }
]

const names = select(users, user => user.name)
// ['Alice', 'Bob', 'Charlie']

带条件过滤

import { select } from 'radash'

const users = [
  { name: 'Alice', age: 25 },
  { name: 'Bob', age: 30 },
  { name: 'Charlie', age: 35 },
  { name: 'Diana', age: 20 }
]

const adultNames = select(
  users,
  user => user.name,
  user => user.age >= 25
)
// ['Alice', 'Bob', 'Charlie']

转换和过滤

import { select } from 'radash'

const products = [
  { name: 'Laptop', price: 999 },
  { name: 'Phone', price: 599 },
  { name: 'Book', price: 29 },
  { name: 'Tablet', price: 399 }
]

const expensiveProducts = select(
  products,
  product => ({ ...product, isExpensive: true }),
  product => product.price > 500
)
// [
//   { name: 'Laptop', price: 999, isExpensive: true },
//   { name: 'Phone', price: 599, isExpensive: true }
// ]

处理嵌套对象

import { select } from 'radash'

const orders = [
  { id: 1, customer: { name: 'Alice', city: 'New York' } },
  { id: 2, customer: { name: 'Bob', city: 'Los Angeles' } },
  { id: 3, customer: { name: 'Charlie', city: 'New York' } }
]

const nyCustomers = select(
  orders,
  order => order.customer.name,
  order => order.customer.city === 'New York'
)
// ['Alice', 'Charlie']

数值计算

import { select } from 'radash'

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

const evenSquares = select(
  numbers,
  n => n * n,
  n => n % 2 === 0
)
// [4, 16, 36, 64, 100]

字符串处理

import { select } from 'radash'

const words = ['hello', 'world', 'javascript', 'typescript', 'react']

const longWords = select(
  words,
  word => word.toUpperCase(),
  word => word.length > 5
)
// ['JAVASCRIPT', 'TYPESCRIPT']

处理日期

import { select } from 'radash'

const events = [
  { title: 'Meeting 1', date: new Date('2023-01-01') },
  { title: 'Meeting 2', date: new Date('2023-01-15') },
  { title: 'Meeting 3', date: new Date('2023-02-01') }
]

const thisMonthEvents = select(
  events,
  event => event.title,
  event => event.date.getMonth() === 0 // 1月
)
// ['Meeting 1', 'Meeting 2']

复杂条件

import { select } from 'radash'

const employees = [
  { name: 'Alice', age: 25, department: 'Engineering', salary: 80000 },
  { name: 'Bob', age: 30, department: 'Sales', salary: 60000 },
  { name: 'Charlie', age: 35, department: 'Engineering', salary: 90000 },
  { name: 'Diana', age: 28, department: 'Marketing', salary: 70000 }
]

const seniorEngineers = select(
  employees,
  emp => ({ ...emp, level: 'Senior' }),
  emp => emp.department === 'Engineering' && emp.age >= 30
)
// [
//   { name: 'Charlie', age: 35, department: 'Engineering', salary: 90000, level: 'Senior' }
// ]

处理空值

import { select } from 'radash'

const items = [
  { name: 'Item 1', category: 'A' },
  { name: 'Item 2', category: null },
  { name: 'Item 3', category: 'B' },
  { name: 'Item 4', category: undefined }
]

const categorizedItems = select(
  items,
  item => item.name,
  item => item.category != null
)
// ['Item 1', 'Item 3']

链式操作

import { select } from 'radash'

const numbers = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

// 先过滤偶数，再转换为字符串
const evenStrings = select(
  numbers,
  n => n.toString(),
  n => n % 2 === 0
)
// ['2', '4', '6', '8', '10']

// 再过滤长度大于1的字符串
const longEvenStrings = select(
  evenStrings,
  s => s,
  s => s.length > 1
)
// ['10']

注意事项

1. 转换函数: 必须提供转换函数
2. 条件函数: 条件函数是可选的
3. 性能: 时间复杂度为 O(n)
4. 类型安全: 支持完整的 TypeScript 类型推断

与其他函数的区别

• select: 同时进行过滤和转换
• map: 只进行转换
• filter: 只进行过滤
• map + filter: 需要两次遍历

性能

• 时间复杂度: O(n)
• 空间复杂度: O(n)
• 适用场景: 数据转换和过滤