Why doesn't this code work?
mtcars %>% select_("starts_with('d')")
Error in eval(expr, envir, enclos) : could not find function "starts_with"
This is simplified example. I am trying to pass the select_ command to a function.
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Joel Kanerva
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3Why not `mtcars %>% select(starts_with('d'))`? – David Arenburg Aug 08 '16 at 10:02
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1Or maybe `mtcars %>% select_(~starts_with('d'))` , if you really want to use `select_` with the underscore, for whatever reason. – RHertel Aug 08 '16 at 10:10
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I'm passing select_ to a function. Bottom example worked. Thank you – Joel Kanerva Aug 08 '16 at 10:52
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It does with `packageVersion("dplyr")` 0.4.3 – NJBurgo Aug 08 '16 at 11:52
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@JoelKanerva Glad to heart that it works. In that case I post my comment as an answer, so that the question can be closed. – RHertel Aug 08 '16 at 14:53
1 Answers
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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").
RHertel
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t/f: select(arg,...) should be replaced with select_(~arg,...) in every instance that's not on the console? your example seems to contradict this page https://www.rdocumentation.org/packages/dplyr/versions/0.7.3/topics/select – 3pitt Oct 18 '17 at 19:27