将列表转换为R中的数据框,并添加包含子列表名称的列

Question

List l有三个字符串,分别命名为一个,两个和三个.我想转换l为数据帧,我需要一个名为的附加列n.

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

我可以使用循环来完成它,但我确信有更有效的方法可以做到这一点.

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

Answer 1

使用基数R,基本上可以用两行来完成.

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

#Create an appropriately sized vector of names
nameVector <- unlist(mapply(function(x,y){ rep(y, length(x)) }, l, n))

#Create the result
resultDF <- cbind.data.frame(unlist(l), nameVector)


> resultDF
  unlist(l) nameVector
1         a        one
2         b        one
3         c        two
4         d        two
5         e        two
6         e      three

Answer 2

stack另一种选择是将列表中每个元素的名称设置为向量后使用：

stack(setNames(l, n))

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