dplyr:如何在函数内部使用 group_by? [英] dplyr: How to use group_by inside a function?

问题描述

我想在另一个函数中使用 dplyr::group_by 函数，但我不知道如何将参数传递给这个函数.

I want to use use the dplyr::group_by function inside another function, but I do not know how to pass the arguments to this function.

有人可以提供一个有效的例子吗?

Can someone provide a working example?

library(dplyr)
data(iris)
iris %.% group_by(Species) %.% summarise(n = n()) # 
## Source: local data frame [3 x 2]
##      Species  n
## 1  virginica 50
## 2 versicolor 50
## 3     setosa 50

mytable0 <- function(x, ...) x %.% group_by(...) %.% summarise(n = n())
mytable0(iris, "Species") # OK
## Source: local data frame [3 x 2]
##      Species  n
## 1  virginica 50
## 2 versicolor 50
## 3     setosa 50

mytable1 <- function(x, key) x %.% group_by(as.name(key)) %.% summarise(n = n())
mytable1(iris, "Species") # Wrong!
# Error: unsupported type for column 'as.name(key)' (SYMSXP)

mytable2 <- function(x, key) x %.% group_by(key) %.% summarise(n = n())
mytable2(iris, "Species") # Wrong!
# Error: index out of bounds

推荐答案

对于编程，group_by_ 是 group_by 的对应物:

For programming, group_by_ is the counterpart to group_by:

library(dplyr)

mytable <- function(x, ...) x %>% group_by_(...) %>% summarise(n = n())
mytable(iris, "Species")
# or iris %>% mytable("Species")

给出:

     Species  n
1     setosa 50
2 versicolor 50
3  virginica 50

更新 在写这篇文章时，dplyr 使用了 %.% ，这是上面最初使用的，但现在 %>% 是受青睐，因此已在上面更改为保持相关性.

Update At the time this was written dplyr used %.% which is what was originally used above but now %>% is favored so have changed above to that to keep this relevant.

更新 2 重组现已弃用，请改用 group_by_.

Update 2 regroup is now deprecated, use group_by_ instead.

更新 3 group_by_(list(...)) 在新版本的 dplyr 中现在变成了 group_by_(...)罗伯托的评论.

Update 3 group_by_(list(...)) now becomes group_by_(...) in new version of dplyr as per Roberto's comment.

更新 4 添加了评论中建议的细微变化.

Update 4 Added minor variation suggested in comments.

更新 5:现在可以使用 rlang/tidyeval 执行此操作:

Update 5: With rlang/tidyeval it is now possible to do this:

library(rlang)
mytable <- function(x, ...) {
  group_ <- syms(...)
  x %>% 
    group_by(!!!group_) %>% 
    summarise(n = n())
}
mytable(iris, "Species")

或传递未评估的 Species，即周围没有引号:

or passing Species unevaluated, i.e. no quotes around it:

library(rlang)
mytable <- function(x, ...) {
  group_ <- enquos(...)
  x %>% 
    group_by(!!!group_) %>% 
    summarise(n = n())
}
mytable(iris, Species)

更新 6:现在有一个 {{...}} 表示法，如果只有一个分组变量:

Update 6: There is now a {{...}} notation that works if there is just one grouping variable:

mytable <- function(x, group) {
  x %>% 
    group_by({{group}}) %>% 
    summarise(n = n())
}
mytable(iris, Species)

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