在Ruby中，如何让我从一个数组的哈希？ [英] In Ruby, how do I make a hash from an array?

问题描述

我有一个简单的数组：

arr = ["apples", "bananas", "coconuts", "watermelons"]

我也有一个函数˚F将在一个字符串输入执行操作，并返回一个值。此操作是非常昂贵的，所以我想memoize的哈希结果。

I also have a function f that will perform an operation on a single string input and return a value. This operation is very expensive, so I would like to memoize the results in the hash.

我知道我可以进行所需的哈希像这样的东西：

I know I can make the desired hash with something like this:

h = {}
arr.each { |a| h[a] = f(a) }

我想要做的是没有初始化小时，这样我可以只写是这样的：

What I'd like to do is not have to initialize h, so that I can just write something like this:

h = arr.(???) { |a| a => f(a) }

可以在做什么？

推荐答案

假设你有一个FUNTASTIC名称的功能：F

Say you have a function with a funtastic name: "f"

def f(fruit)
   fruit + "!"
end

arr = ["apples", "bananas", "coconuts", "watermelons"]
h = Hash[ *arr.collect { |v| [ v, f(v) ] }.flatten ]

会给你：

{"watermelons"=>"watermelons!", "bananas"=>"bananas!", "apples"=>"apples!", "coconuts"=>"coconuts!"}

更新：

正如评论中提到，红宝石1.8.7引入了一个更好的语法如下：

As mentioned in the comments, Ruby 1.8.7 introduces a nicer syntax for this:

h = Hash[arr.collect { |v| [v, f(v)] }]

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