[Rd] improve 'package not installed' load errors?

[Fox, John]

Dear Kevin,

As others have mentioned, it's my sense that this kind of error has become more frequent -- at least I see students who encounter these errors more frequently. I agree that a less cryptic error message might help.

Best,
 John
--------------------------------------
John Fox, Professor
McMaster University
Hamilton, Ontario, Canada
Web: socserv.mcmaster.ca/jfox



> -----Original Message-----
> From: R-devel [mailto:r-devel-bounces at r-project.org] On Behalf Of Kevin
> Ushey
> Sent: Monday, October 24, 2016 1:51 PM
> To: R-devel <r-devel at r-project.org>
> Subject: [Rd] improve 'package not installed' load errors?
> 
> Hi R-devel,
> 
> One of the more common issues that new R users see, and become stumped
> by, is error messages during package load of the form:
> 
> > library(ggplot2)
> Error in loadNamespace(j <- i[[1L]], c(lib.loc, .libPaths()),
> versionCheck = vI[[j]]) :
>   there is no package called 'Rcpp'
> Error: package or namespace load failed for 'ggplot2'
> 
> Typically, error messages of this form are caused simply by one or more
> dependent packages (in this case, 'Rcpp') not being installed or
> available on the current library paths. (A side question, which I do not
> know the answer to, is how users get themselves into this state.)
> 
> I believe it would be helpful for new users if the error message
> reported here was a bit more direct, e.g.
> 
> > library(ggplot2)
> Error: 'ggplot2' depends on package 'Rcpp', but 'Rcpp' is not installed
> consider installing 'Rcpp' with install.packages("Rcpp")
> 
> In other words, it might be helpful to avoid printing the
> 'loadNamespace()' call on error (since it's mostly just scary /
> uninformative), and check up-front that the package is installed before
> attempting to call 'loadNamespace()'. I'm sure a number of novice users
> will still just throw their hands up in the air and say "I don't know
> what to do", but I think this would help steer a number of users in the
> right direction.
> 
> (The prescription to suggest installing a package from CRAN if available
> might be a step too far, but I think making it more clear that the error
> is due to a missing dependent package would help.)
> 
> Any thoughts?
> Kevin
> 
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