将列表转换为R中的数据框，并添加带有子列表名称的列 [英] Convert list to dataframe in R and add column with names of sub-lists

问题描述

列表l具有三个分别命名为一，二和三的字符串.我想将l转换为数据框，并且我需要在n中具有名称的附加列.

List l has three strings that are named one, two, and three, respectively. I want to convert l to a dataframe, and I need an additional column with the names in n.

l <- list(c("a", "b"), c("c", "d", "e"), c("e"))
n <- c("one", "two", "three")

我可以使用循环来做到这一点，但是我敢肯定，有更有效的方法可以做到这一点.

I can do it using a loop, but I'm sure there are more efficient ways of doing this.

out <- NULL
for (i in 1:length(n)){
  step <- rep(n[i], length(l[[i]]))
  out <- c(out, step)}

df <- as.data.frame(unlist(l))
df$n <- out
df

#  unlist(l)     n
#1         a   one
#2         b   one
#3         c   two
#4         d   two
#5         e   two
#6         e three

推荐答案

另一种选择是在将列表中每个元素的名称设置为向量之后使用stack:

Another option is to use stack after setting the name for each element of the list to be the vector:

stack(setNames(l, n))

#  values   ind
#1      a   one
#2      b   one
#3      c   two
#4      d   two
#5      e   two
#6      e three

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