[R] When using require(), why do I get the error message "Error in if (!loaded) { : the condition has length > 1" ?

[Andrew Simmons]

In the first one, the argument is a character vector of length 1, so the
code works perfectly fine.

The second is a call, and when coerced to a character vector should look
like

c("[", "packages_i_want_to_use", "1")

You can try this yourself with quote(packages_i_want_to_use[1]) which
returns its first argument, unevaluated.

On Mon, Oct 24, 2022, 12:46 Kelly Thompson <kt1572757 using gmail.com> wrote:

> Thanks!
>
> # Please, can you help me understand why
> require( 'base' ) # works, but
> require( packages_i_want_to_use[1] ) # does not work?
>
> # In require( 'base' ), what is the "first argument"?
>
> On Mon, Oct 24, 2022 at 12:29 PM Andrew Simmons <akwsimmo using gmail.com>
> wrote:
> >
> > require(), similarly to library(), does not evaluate its first argument
> UNLESS you add character.only = TRUE
> >
> > require( packages_i_want_to_use[1], character.only = TRUE)
> >
> >
> > On Mon, Oct 24, 2022, 12:26 Kelly Thompson <kt1572757 using gmail.com> wrote:
> >>
> >> # Below, when using require(), why do I get the error message "Error
> >> in if (!loaded) { : the condition has length > 1" ?
> >>
> >> # This is my reproducible code:
> >>
> >> #create a vector with the names of the packages I want to use
> >> packages_i_want_to_use <- c('base', 'this_pac_does_not_exist')
> >>
> >> # Here I get error messages:
> >> require( packages_i_want_to_use[1] )
> >> #Error in if (!loaded) { : the condition has length > 1
> >>
> >> require( packages_i_want_to_use[2] )
> >> #Error in if (!loaded) { : the condition has length > 1
> >>
> >> # Here I get what I expect:
> >> require('base')
> >>
> >> require('this_pac_does_not_exist')
> >> #Loading required package: this_pac_does_not_exist
> >> #Warning message:
> >> #In library(package, lib.loc = lib.loc, character.only = TRUE,
> >> logical.return = TRUE,  :
> >> #  there is no package called ‘this_pac_does_not_exist’
> >>
> >> ______________________________________________
> >> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> >> https://stat.ethz.ch/mailman/listinfo/r-help
> >> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> >> and provide commented, minimal, self-contained, reproducible code.
>
> ______________________________________________
> R-help using r-project.org mailing list -- To UNSUBSCRIBE and more, see
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>

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