select columns based on multiple strings with dplyr contains()

Question

I want to select multiple columns based on their names with a regex expression. I am trying to do it with the piping syntax of the dplyr package. I checked the other topics, but only found answers about a single string.

With base R:

library(dplyr)    
mtcars[grepl('m|ar', names(mtcars))]
###                      mpg am gear carb
### Mazda RX4           21.0  1    4    4
### Mazda RX4 Wag       21.0  1    4    4

However it doesn't work with the select/contains way:

mtcars %>% select(contains('m|ar'))
### data frame with 0 columns and 32 rows

What's wrong?

akrun · Accepted Answer · 2015-03-12 19:15:46Z

118

You can use matches

 mtcars %>%
        select(matches('m|ar')) %>%
        head(2)
 #              mpg am gear carb
 #Mazda RX4      21  1    4    4
 #Mazda RX4 Wag  21  1    4    4

According to the ?select documentation

‘matches(x, ignore.case = TRUE)’: selects all variables whose name matches the regular expression ‘x’

Though contains work with a single string

mtcars %>% 
       select(contains('m'))

edited Mar 12, 2015 at 19:15

answered Mar 12, 2015 at 19:10

akrun

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9 Comments

agenis - code en bois Over a year ago

Thank you @akrun, i feel stupid now :-). But one question, still: given that, why should we even use contains(), if matches() does the same and even better?

hadley Over a year ago

@agenis Because you might want to match "." and not have to think about how to escape it in a regular expression

akrun Over a year ago

@MichaelBellhouse In that case you use paste ie. paste(yourvec, collapse="|") and use that in matches

Michael Bellhouse Over a year ago

akrun, thank you so much. I;ve been doing a lot of digging and experimenting for this. All the best.

Michael Bellhouse Over a year ago

equivalent_for_filter <- df %>% filter(!grepl(paste(exclude_filter, collapse="|"),variable))

|

Vinícius Félix · Accepted Answer · 2021-09-24 09:26:30Z

23

You can use contains from package dplyr, if you give a vector of text options, like this:

mtcars %>% 
       select(contains(c("m", "ar"))

edited Sep 24, 2021 at 9:26

Vinícius Félix

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answered Sep 24, 2021 at 7:09

Nicki Norris

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2 Comments

Community Over a year ago

Your answer could be improved with additional supporting information. Please edit to add further details, such as citations or documentation, so that others can confirm that your answer is correct. You can find more information on how to write good answers in the help center.

Faustin Gashakamba Over a year ago

contains() with a vector of as many element as you want works just fine. Actually, matches() should be reserved for cases where you need complex matching using REGEX

Muthoni Thiong'o · Accepted Answer · 2021-07-19 13:12:26Z

4

You could still use grepl() from base R.

df <- mtcars[ , grepl('m|ar', names(mtcars))]

...which returns a subset dataframe, df, containing columns with m or ar in the column names

answered Jul 19, 2021 at 13:12

Muthoni Thiong'o

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Comments

redantman · Accepted Answer · 2023-03-28 14:54:52Z

1

here's an alternative

mtcars %>% 
    select(contains('m') | contains('ar')) %>% 
    head(2)

#             mpg am gear carb
# Mazda RX4      21  1    4    4
# Mazda RX4 Wag  21  1    4    4

answered Mar 28, 2023 at 14:54

redantman

311 bronze badge

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