如何在函数中使用dplyr :: group_by

Question

我想创建一个函数,它将生成一个基于一个或多个分组变量计数的表.我发现这篇文章在一个函数中使用dplyr group_by,如果我将函数传递给单个变量名,它就可以工作

library(dplyr)
l <- c("a", "b", "c", "e", "f", "g")
animal <- c("dog", "cat", "dog", "dog", "cat", "fish")
sex <- c("m", "f", "f", "m", "f", "unknown")
n <- rep(1, length(animal))
theTibble <- tibble(l, animal, sex, n)


countString <- function(things) {
  theTibble %>% group_by(!! enquo(things)) %>% count()
}

countString(animal)
countString(sex)

这很好用,但我不知道如何传递函数两个变量.这种作品:

countString(paste(animal, sex))

它给了我正确的计数,但返回的表将动物和性变量折叠成一个变量.

# A tibble: 4 x 2
# Groups:   paste(animal, sex) [4]
  `paste(animal, sex)`    nn
  <chr>                <int>
1 cat f                    2
2 dog f                    1
3 dog m                    2
4 fish unknown             1

传递函数的语法是用逗号分隔的两个单词的语法是什么？我想得到这个结果:

# A tibble: 4 x 3
# Groups:   animal, sex [4]
  animal sex        nn
  <chr>  <chr>   <int>
1 cat    f           2
2 dog    f           1
3 dog    m           2
4 fish   unknown     1

Answer 1

您可以使用group_by_at和列索引,例如:

countString <- function(things) {
  index <- which(colnames(theTibble) %in% things)
  theTibble %>% 
       group_by_at(index) %>% 
       count()
}

countString(c("animal", "sex"))

## A tibble: 4 x 3
## Groups:   animal, sex [4]
#  animal sex        nn
#  <chr>  <chr>   <int>
#1 cat    f           2
#2 dog    f           1
#3 dog    m           2
#4 fish   unknown     1