How to use regular expressions with dplyr's select helper functions

Question

It is straightforward to use dplyr to select columns using various helper functions, such as contains(). In the help file for these functions the argument is referred to as a 'literal string'. However, is it possible to use regular expressions instead?

The following example works:

library(dplyr)
iris %>%
   select(contains("Species"))

The following regex example does not:

# Select all column names that end with lower case "s"
iris %>%
   select(contains("s$"))

# Not run
data frame with 0 columns and 150 rows

I would like to know if using regular expressions in dplyr select helper functions is possible and, if so, their implementation.

If this isn't possible, I will except an answer using an alternative method (e.g., base or data.table). For background, my ultimate aim is to use a summarise_at() function or equivalent to sum all columns that end in a number (i.e, regexp [0-9]$).

Answer 1

The select helper function matches() is available to match regular expressions:

library(dplyr)

out <- select(iris, matches("s$"))

head(out)
#>   Species
#> 1  setosa
#> 2  setosa
#> 3  setosa
#> 4  setosa
#> 5  setosa
#> 6  setosa

Answer 2

With dplyr, one can use ends_with:

iris %>% 
  select(ends_with("s")) %>% 
   head(3)
  Species
1  setosa
2  setosa
3  setosa

With base and grepl:

head(iris[grepl("s$",names(iris),ignore.case = FALSE)])
  Species
1  setosa
2  setosa
3  setosa
4  setosa
5  setosa
6  setosa

Or using purrr:

iris %>% 
   purrr::keep(grepl("s$",names(.))) %>% 
   head()
  Species
1  setosa
2  setosa
3  setosa
4  setosa
5  setosa
6  setosa