Using select_ and starts_with R

Question

Why doesn\'t this code work?

mtcars %>% select_(\"starts_with(\'d\')\")

Error in eval(expr, envir, enclos) : could not find function \"starts_with\"
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Answer 1

The difference between select() and select_() is their non-stadard / standard evaluation of the argument. If a function like starts_with() is used as an argument of select_() it should be quoted with a tilde:

library(dplyr)
mtcars %>% select_(~starts_with('d'))

This yields the same output as the normal use of select:

identical(mtcars %>% select_(~starts_with('d')), mtcars %>% select(starts_with('d')))
#[1] TRUE

For more information see the vignette on non-standard evaluation: vignette("nse").