R quo_name等同于quos [英] R quo_name equivalent of quos

问题描述

在使用dplyr编程之后，我注意到一个人可以使用quo_name添加名称.我想知道如何对多个列执行此操作，例如.就像各种各样的quos_name一样.例如:

Hi following Programming with dplyr I noticed that one can add a name using quo_name. I was wondering how to do this for multiple columns, eg. like a quos_name of sorts. E.g.:

   my_mutate <- function(df, expr) {
  expr <- enquo(expr)
  mean_name <- paste0("mean_", quo_name(expr))
  sum_name <- paste0("sum_", quo_name(expr))
  
  mutate(df, 
    !!mean_name := mean(!!expr), 
    !!sum_name := sum(!!expr)
  )
}

成为

   my_mutate <- function(df, ...) {
  exprs <-quos(...)
  mean_names <- paste0("mean_", quos_name(exprs))
  sum_names <- paste0("sum_", quos_name(exprs))
  
  mutate(df, 
    !!!mean_names := mean(!!!exprs), 
    !!!sum_names := sum(!!!exprs)
  )
}

即.为...中指定的所有列添加均值和求和列 ，当然这仅是一个示例，quos_names不存在.如果有办法的话，这将非常有帮助.

ie. adding the mean and sum columns for all columns specified in ... , of course this is only as an example and quos_names don't exist. It would be very helpful if there is a way of doing this.

例如，我知道可以在data.table DT[,(Col_names):=lapply(Cols,mean)]中执行类似的操作(此代码不起作用，但是我之前已经执行过类似的操作).

I know it is possible to do something like this in data.table DT[,(Col_names):=lapply(Cols,mean)] for instance (This code does not work, but I have done something like this before).

推荐答案

免责声明:虽然我认为@aosmith提出的mutate_at是最好，最简单的解决方案，但我认为这可能是有启发性的了解如果mutate_at不存在，如何使用rlang工具解决该问题.为了科学！

DISCLAIMER: While mutate_at proposed by @aosmith is in my opinion the best and simplest solution, I think it might be instructive to see how the problem could be approached using rlang tools, if mutate_at didn't exist. For science!

如评论中所述，您将需要研究purrr::map()系列功能.您还会遇到!!!mean_names := mean(!!!exprs)的另一个问题，因为!!!拼接运算符不能在分配的左手使用.

As mentioned in the comments, you will want to look into purrr::map() family of functions. You will also run into a separate problem with !!!mean_names := mean(!!!exprs) because the !!! splice operator cannot be used on the left hand of the assignment.

最好的rlang方法是将mutate表达式组成一个命名列表.使用quo执行表达式算术，并使用stringr::str_c(或一直在执行paste0)进行字符串算术:

The best rlang approach is to compose your mutate expressions as a named list. Use quo to perform expression arithmetic and stringr::str_c (or paste0 as you've been doing) for string arithmetic:

library( tidyverse )

my_mutate <- function(df, ...) {
  exprs <- enquos(...)

  mean_exprs <- set_names(
    map(exprs, ~quo(mean(!!.x))),               # mpg becomes mean(mpg)
    str_c("mean_", map_chr(exprs, quo_name)) )  # mpg becomes "mean_mpg"

  sum_exprs <- set_names(
    map(exprs, ~quo(sum(!!.x))),                # mpg becomes sum(mpg)
    str_c("sum_", map_chr(exprs, quo_name)) )   # mpg becomes "sum_mpg"

  mutate(df, !!!mean_exprs, !!!sum_exprs)
}

mtcars %>% my_mutate( mpg, cyl )
#    mpg cyl disp  hp ... mean_mpg mean_cyl sum_mpg sum_cyl
# 1 21.0   6  160 110 ... 20.09062   6.1875   642.9     198
# 2 21.0   6  160 110 ... 20.09062   6.1875   642.9     198
# 3 22.8   4  108  93 ... 20.09062   6.1875   642.9     198
# 4 21.4   6  258 110 ... 20.09062   6.1875   642.9     198

---

奖金::您会注意到我们在上面的表达式定义中重复了一段代码.我们可以将其提取到一个独立的函数中，该函数使用所提供的函数自动构造表达式并相应地命名这些表达式:

---

BONUS: You will notice that we are repeating a chunk of code in our definition of expressions above. We can pull that out into a standalone function that automatically constructs expressions with the provided function and names those expressions accordingly:

mutator <- function(f, ...) {
  f_expr <- enquo(f)
  exprs <- enquos(...)

  ## Same code as in my_mutate above, but with an arbitrary function
  set_names(
    map( exprs, ~quo((!!f_expr)(!!.x)) ),
    str_c( quo_name(f_expr), "_", map_chr(exprs, quo_name) )
  )
}

## Example usage
mutator( sd, mpg, cyl )
# $sd_mpg
# <quosure>
#   expr: ^^sd(^mpg)
#   env:  0x555e05260020

# $sd_cyl
# <quosure>
#   expr: ^^sd(^cyl)
#   env:  0x555e05273af8

我们现在可以使用新的mutator函数将my_mutate重新定义为简单的单行代码:

We can now use the new mutator function to re-define my_mutate as a simple one-liner:

my_mutate2 <- function(df, ...) {
  mutate( df, !!!mutator(mean, ...), !!!mutator(sum, ...) )
}

这篇关于R quo_name等同于quos的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！