从列表中删除特定于行的项目

Question

我想从前3列（＆＃39; group＆＃39;，＆＃39; animal＆＃39;和＆＃39;）中创建最后一列（＆＃39; desired_result＆＃39;）全＆＃39）。下面是可重复示例的代码。

library(data.table)
data = data.table(group = c(1,1,1,2,2,2), animal = c('cat', 'dog', 'pig', 'giraffe', 'lion', 'tiger'), desired_result = c('dog, pig', 'cat, pig', 'cat, dog', 'lion, tiger', 'giraffe, tiger', 'giraffe, lion'))
data[, full := list(list(animal)), by = 'group']
data = data[, .(group, animal, full, desired_result)]

data
    group  animal               full   desired_result
1:     1     cat          cat,dog,pig     dog, pig
2:     1     dog          cat,dog,pig     cat, pig
3:     1     pig          cat,dog,pig     cat, dog
4:     2 giraffe   giraffe,lion,tiger    lion, tiger
5:     2    lion   giraffe,lion,tiger    giraffe, tiger
6:     2   tiger   giraffe,lion,tiger    giraffe, lion

基本上，我想修改完整的＆＃39;所以它不包括相应的“动物”。我已尝试使用这些列的列表和字符版本的各种lapply命令，但无法解决此问题。

Answer 1

这是一种可能的方法

data[, desired_result := {
        temp <- unique(unlist(full)) 
        toString(temp[-match(animal, temp)])
        }, by = .(group, animal)]
data
#    group  animal               full desired_result
# 1:     1     cat        cat,dog,pig       dog, pig
# 2:     1     dog        cat,dog,pig       cat, pig
# 3:     1     pig        cat,dog,pig       cat, dog
# 4:     2 giraffe giraffe,lion,tiger    lion, tiger
# 5:     2    lion giraffe,lion,tiger giraffe, tiger
# 6:     2   tiger giraffe,lion,tiger  giraffe, lion

Answer 2

另一种选择：

data[, desired := .(Map(setdiff, list(animal), as.list(animal))), by = group]

#or if starting from full
data[, desired := .(Map(setdiff, full, animal))]

（回收魔法让第一个版本起作用）

Answer 3

我也找到了一种方法！

通过将'animal'变成一个列表，我可以使用mapply。

data$animal = strsplit(data$animal, ' ')
data$check = mapply(function(x, y) {list(x[x != y]) }, data$full, data$animal)

data
group  animal               full desired_result         check
1:     1     cat        cat,dog,pig       dog, pig       dog,pig
2:     1     dog        cat,dog,pig       cat, pig       cat,pig
3:     1     pig        cat,dog,pig       cat, dog       cat,dog
4:     2 giraffe giraffe,lion,tiger    lion, tiger    lion,tiger
5:     2    lion giraffe,lion,tiger giraffe, tiger giraffe,tiger
6:     2   tiger giraffe,lion,tiger  giraffe, lion  giraffe,lion