dplyr 的 mutate_each 在函数中有效但 matches() 找不到参数

Question

在尝试解决时，我遇到了 dplyr 的 mutate_each 问题。我想在函数中使用它并将参数传递给它。 funs() 成功，但 matches().

失败

让我展示一个简单的例子，其中的任务是将一些标签附加到一些变量的值。

library(dplyr) 
mydf <- data.frame(this_var1 = c("a", "b", "c", "d", "e"), 
                   this_var2 = c("b", "c", "d", "e", "f"),
                   that_var1 = c("x", "y", "z", "w", "u"))

mymutate1 <- function(data, tag) {
  data %>% mutate_each(funs(paste0(., tag)))
}

mymutate1(mydf, "_foo")
  this_var1 this_var2 that_var1
1     a_foo     b_foo     x_foo
2     b_foo     c_foo     y_foo
3     c_foo     d_foo     z_foo
4     d_foo     e_foo     w_foo
5     e_foo     f_foo     u_foo

这很有魅力。但是，如果我还尝试控制应为哪些变量应用转换，则会失败。

mymutate2 <- function(data, tag, m) {
  data %>% mutate_each(funs(paste0(., tag)), matches(m))
}
mymutate2(mydf, "_foo", "this")

这会产生以下错误：Error in is.string(match) : object 'm' not found。为什么 tag 被发现而 m 没有？

代码本身按预期工作：

mydf %>% mutate_each(funs(paste0(., "_foo")), matches("this"))
  this_var1 this_var2 that_var1
1     a_foo     b_foo         x
2     b_foo     c_foo         y
3     c_foo     d_foo         z
4     d_foo     e_foo         w
5     e_foo     f_foo         u

Answer 1

您将要使用 mutate_each 的 Standard Evaluation (SE) 版本——即 mutate_each_:

mymutate2 <- function(data, tag, m) {
  data %>% mutate_each_(funs(paste0(., tag)), ~matches(m))
}

为了更加清楚，以下是等效的：

mymutate3 <- function(data, tag, m) {
  data %>% mutate_each_(~paste0(., tag), ~matches(m))
}

根据 vignette:

"It’s best to use a formula [ ~ as opposed to quote() or using strings "" ], because a formula captures both the expression to evaluate, and the environment in which it should be a evaluated...Using anything other than a formula will fail because it doesn't know which environment to look in."

dplyr 的 mutate_each 在函数中有效但 matches() 找不到参数

dplyr's mutate_each within function works but matches() does not find argument

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