r - 从 for 循环内的列表列表中删除元素

Question

我有一个命名的列表(数据框)列表。

l_of_lists <- list(
  fruits = list(
      red = data.frame("apple", "cherry", "strawberry"),
      yellow = data.frame("banana", "lemon"),
      orange = data.frame("orange", "grapefruit", "blood orange")),
  colors = list(
      green = data.frame("light green", "green", "dark green"),
      red = data.frame("red", "dark red"),
      blue = data.frame("light blue", "blue", "dark blue")),
  places = list(
    inside = data.frame("living room", "bathrooom", "kitchen"),
    outside = data.frame("garden", "yard"),
    neighborhood = data.frame("playground", "shop", "school"))
  )

我正在循环 l_of_lists 的 sublists 以确定每个数据帧的列数，并且我想删除每个不满足条件的 sublist (在本例中它有三列)。

使用以下代码:

for (ls in l_of_lists){
  for (sublist in ls){
    if (!ncol(sublist) == 3)
    {
      print(ncol(sublist))
      #sublist <- NULL # this does achieve the desired result
    }
  }
}

如何删除我用条件标识的子列表？
(我确信有一种更有效的方法来实现这一点，我很高兴收到有关此的提示。)

Answer 1

将没有 3 列的元素称为更容易:

lapply(l_of_lists,function(i)i[sapply(i,length)==3])

使用 sapply，您可以遍历 l_of_list 的每个元素以获取列数向量。您可以使用它对具有 3 列的那些进行子集化。

如果你想删除，试试这个

l_of_lists = lapply(l_of_lists,function(i)i[sapply(i,length)==3])