dplyr组按描述为字符串向量的同名命名 [英] dplyr group by colnames described as vector of strings

问题描述

我正在尝试在数据框中对多列进行group_by操作，并且无法在group_by函数中写出每个列名称，因此我想将列名称称为矢量，如下所示：

I'm trying to group_by multiple columns in my data frame and I can't write out every single column name in the group_by function so I want to call the column names as a vector like so:

cols <- colnames(mtcars)[grep("[a-z]{3,}$", colnames(mtcars))]
mtcars %>% filter(disp < 160) %>% group_by(cols) %>% summarise(n = n())

这将返回错误：

Error in mutate_impl(.data, dots) : 
  Column `mtcars[colnames(mtcars)[grep("[a-z]{3,}$", colnames(mtcars))]]` must be length 12 (the number of rows) or one, not 7

我绝对想使用dplyr函数来执行此操作，但无法弄清楚。 p>

I definitely want to use a dplyr function to do this, but can't figure this one out.

推荐答案

您可以使用 group_by_at ，在其中可以传递列的字符向量名称作为组变量：

You can use group_by_at, where you can pass a character vector of column names as group variables:

mtcars %>% 
    filter(disp < 160) %>% 
    group_by_at(cols) %>% 
    summarise(n = n())
# A tibble: 12 x 8
# Groups:   mpg, cyl, disp, drat, qsec, gear [?]
#     mpg   cyl  disp  drat  qsec  gear  carb     n
#   <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <int>
# 1  19.7     6 145.0  3.62 15.50     5     6     1
# 2  21.4     4 121.0  4.11 18.60     4     2     1
# 3  21.5     4 120.1  3.70 20.01     3     1     1
# 4  22.8     4 108.0  3.85 18.61     4     1     1
# ...

或者您可以移动列选择在 group_by_at 中使用 vars 并选择列辅助函数：

Or you can move the column selection inside group_by_at using vars and column select helper functions:

mtcars %>% 
    filter(disp < 160) %>% 
    group_by_at(vars(matches('[a-z]{3,}$'))) %>% 
    summarise(n = n())

# A tibble: 12 x 8
# Groups:   mpg, cyl, disp, drat, qsec, gear [?]
#     mpg   cyl  disp  drat  qsec  gear  carb     n
#   <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <dbl> <int>
# 1  19.7     6 145.0  3.62 15.50     5     6     1
# 2  21.4     4 121.0  4.11 18.60     4     2     1
# 3  21.5     4 120.1  3.70 20.01     3     1     1
# 4  22.8     4 108.0  3.85 18.61     4     1     1
# ...

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