获得序列中一个项目的出现的位置 [英] getting the positions of the occurrences of one item in a sequence

问题描述

从aa序列，我需要获取给定项目出现的所有位置。

From a a sequence, I need to fetch all the positions of the occurrence of a given item.

我问自己，如果这是一个很好的方法来解决问题：

I'm asking myself if this is a good way to solve the problem:

(defn get-positions [item coll]
  (->> (map-indexed vector coll)
       (filter (fn [[_ v]] (= item v)))
       (map first)))

这也适用于字符串，它们将被第一个映射转换为序列。但是，如果我知道输入是字符串，这个问题会有更多的字符串特定的方法吗？

This also works for strings, they'll be transformed to a sequence by the first map. However, if I know the input's are strings, would there be a more string specific approach for this problem?

推荐答案

有一个一般的解决问题的方法，你为什么要花更多的精力去设想一个更具体的一个？

Since you already have a general solution to the problem, why would you want to spend more effort to try to come up with a more specific one? The benefits of doing so here are negligible.

只是出于种种原因，这里是另一种实现你的函数的方法：

Just for variety's sake, here's another way to implement your function:

(defn positions [x coll]
  (keep-indexed #(when (= x %2) %1) coll))

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