lapply/purrr :: map之类的函数默认允许访问索引? [英] lapply / purrr::map like function that allows access to the index by default?

问题描述

有一个变通办法，允许在s/lapply内部访问索引

例如

x <- list(a=11,b=12,c=13) 
lapply(seq_along(x), function(y, n, i) { paste(n[[i]], y[[i]]) }, y=x, n=names(x))

是否有像s/lapply(或类似 purrr :: map())之类的函数，该函数允许以最简单的方式访问索引，我想这只是简单地提供所需的初始函数调用的名称，仅此而已；

Is there any function like s/lapply (or like purrr::map()) which allows access to the index in the simplest way possible, which I guess would be to simply supply its desired name to the initial function call and nothing more;

map_with_index <- function(.x, .f, index) {
  # Same as purrr::map()
  # ..but whatever string is provided to 'index' parameter becomes the index
  # and is accessible inside the function
  }

是否已经存在某些东西，或者可以定义一个执行此操作的自定义函数?

Does something already exist, or is it possible to define a custom function that does this?

注意:有人可能会说上面的s/lapply技术可以达到要求.但是反驳的说法是，即使在MRE中，它也会增加不必要的复杂性，更不用说在复杂的现实生活中使用了，因此，进行简化很有价值.

Note: One could argue that the s/lapply technique above achieves what's required. But the counter argument is that it adds unwanted complexity even in its MRE, let alone in complicated real life settings, hence, a simplification would be valuable.

推荐答案

您需要查看 purrr :: imap 函数系列.这是一个简单的示例:

You need to look at the purrr::imap family of functions. Here is a simple example:

set.seed(123)
s <- sample(10)
purrr::imap_chr(s, ~ paste0(.y, ": ", .x))

输出

[1] "1: 3"  "2: 10" "3: 2"  "4: 8"  "5: 6"  "6: 9"  "7: 1"  "8: 7"  "9: 5"  "10:4"

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