在列表中查找矢量元素的索引 [英] Find indices of vector elements in a list

问题描述

我有这个玩具角色向量:

I have this toy character vector:

a = c("a","b","c","d","e","d,e","f")

其中某些元素用逗号(例如"d，e")连接起来

in which some elements are concatenated with a comma (e.g. "d,e")

以及包含该向量的唯一元素的列表，在这种情况下，如果使用逗号串联元素，则我不会保留它们的各个组成部分.

and a list that contains the unique elements of that vector, where in case of comma concatenated elements I do not keep their individual components.

这是列表:

l = list("a","b","c","d,e","f")

我正在寻找一种有效的方法来获取l列表中a的元素的索引.对于a中由逗号连接的元素表示的a元素，它应返回l中这些逗号连接的元素的索引.

I am looking for an efficient way to obtain the indices of the elements of a in the l list. For elements of a that are represented by the comma concatenated elements in l it should return the indices of the these comma concatenated elements in l.

因此此函数的输出为:

c(1,2,3,4,4,4,5)

如您所见，它返回a元素的索引4:"d"，"e"和"d，e"

As you can see it returns index 4 for a elements: "d", "e", and "d,e"

推荐答案

您可以将策略与因素结合使用.首先，使用

You could use a strategy with factors. First, find the index for each element in your list with

l <- list("a","b","c","d,e","f")
idxtr <- Map(function(x) unique(c(x, strsplit(x, ",")[[1]])), unlist(l))

这将为l中的每个项目建立一个列表，以及每个元素的所有可能匹配项.然后我们取向量a并用这些水平创建一个因子，然后根据我们刚刚构建的列表重新分配

This build a list for each item in l along with all possible matches for each element. Then we take the vector a and create a factor with those levels, and then reassign based on the list we just build

a <- c("a","b","c","d","e","d,e","f")
a <- factor(a, levels=unlist(idxtr));
levels(a) <- idxtr
as.numeric(a)
# [1] 1 2 3 4 4 4 5

最后，要获取索引，我们在因子上使用as.numeric

finally, to get the index, we use as.numeric on the factor

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