在R中搜索列表条目的索引 [英] Search for index of a list entry in R

问题描述

给定一个R列表，我希望找到给定列表条目的索引.例如，对于条目"36"，我希望输出为"2".另外，如何使用lapply并行执行此类查询?

Given an R list, I wish to find the index of a given list entry. For example, for entry "36", I want my output to be "2". Also, how could I do such queries in parallel using lapply?

> list

$`1`
[1] "7"  "12" "26" "29"

$`2`
[1] "11" "36"

$`3`
[1] "20" "49"

$`4`
[1] "39" "41"

推荐答案

这是一种单行代码，它允许(可能吗?)列表中的多个元素可能包含您要搜索的字符串:

Here's a one-liner that allows for the (likely?) possibility that more than one element of the list will contain the string for which you're searching:

## Some example data
ll <- list(1:4, 5:6, 7:12, 1:12)
ll <- lapply(ll, as.character)

which(sapply(ll, FUN=function(X) "12" %in% X))
# [1] 3 4

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