clarify error when rbindlist(l) is not a list()

[ajdamico]

hi, in the code below, users hit this error message that says data.table and data.frame objects are OK when they're actually not.. thanks for the amazing software!

library(data.table)


# correct error message
rbindlist( list( 1 ) )
# Error in rbindlist(x) : 
#   Item 1 of input is not a data.frame, data.table or list


# confusing error message, since item 1 is a data.frame
rbindlist( mtcars )
# Error in rbindlist(x) : 
#   Item 1 of input is not a data.frame, data.table or list

class(mtcars)
# [1] "data.frame"

x <- data.table( mtcars )

# confusing error message, since item 1 is a data.table
rbindlist( x )
# Error in rbindlist(x) : 
#   Item 1 of input is not a data.frame, data.table or list

class( x )
# [1] "data.table" "data.frame"


# works as expected
rbindlist( list( mtcars ) )
rbindlist( list( x ) )

[jangorecki]

Thanks for PR, I left comment how to fix failure of test 682

[codecov]

Codecov Report

Merging #3638 into master will decrease coverage by <.01%.
The diff coverage is 50%.

@@            Coverage Diff             @@
##           master    #3638      +/-   ##
==========================================
- Coverage   98.19%   98.18%   -0.01%     
==========================================
  Files          66       66              
  Lines       12923    12925       +2     
==========================================
+ Hits        12690    12691       +1     
- Misses        233      234       +1

Impacted Files	Coverage Δ
R/data.table.R	97.69% <50%> (-0.05%)	⬇️

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[jangorecki]

Looks like code there are not unit test for error message added in this PR, could you add one?

[ajdamico]

@jangorecki hi, i hope d064de2 works? thanks again

[mattdowle]

Great. Thanks @ajdamico. I've invited you to be project member so that next time you can create a branch directly in the main project. This makes it easier to work on each other's branches. You'll need to accept the invitation before it is applied (I think it's a notification in the top right of GitHub). Thanks again and welcome!

[mattdowle]

This was a code contribution, so I'm sorry @ajdamico, I should have added you to DESCRIPTION as a contributor at the time. I'll correct my mistake now in a commit to master linking to this PR.
Found as a result of following up on discussion at the end of #1236.
(This contribution was after the license change from GPL to MPL so it doesn't need to be included in the forthcoming retrospective-permission PR.)

[ajdamico]

we use this software every day. thank you!!