foverlaps returns error when keyed on "start" "end" and also contains columns "i.start" "i.end"

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
r
Domain
data

Research direction

Start by reproducing the supplied data.table and foverlaps example, then inspect how foverlaps handles existing i.start and i.end columns. Review the help file and decide whether the intended resolution is an early, clear naming-conflict error or continued prefixing; done means the conflict no longer produces the reported duplicate-column error and the behavior is documented.

Written by the indexing model from the issue text.

Description

non-equi joins

It's not unreasonable to assume the user's input data.table(s) to the arguments of foverlaps already contain columns prepended with "i.". This could occur in the case of repeated calls to foverlaps.

If it is intended behavior for column names "i.<interval key variable 1>", and "i.<interval key variable 2>" to be reserved, then at the very least there should be an error check at the top of the function (so the user doesn't need to wait for computation to learn there's a naming conflict) with a clear error message. This should be called out in the help file as well.

Alternatively, the function could just continue to prepend the column name with "i." until it finds one that's not already in use (e.g. using a while statement).

library(data.table)
x <- data.table(start=1:10,end=1:10,i.start=1:10,i.end=1:10)
setkey(x,start,end)
foverlaps(x,x)

error message:

Error in setcolorder(ans, c(xcols1, ycols, xcols2)) : 
  neworder contains duplicates

sessionInfo():

R version 3.5.3 (2019-03-11)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows Server 2008 R2 x64 (build 7601) Service Pack 1

Matrix products: default

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252    LC_MONETARY=English_United States.1252
[4] LC_NUMERIC=C                           LC_TIME=English_United States.1252    

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] data.table_1.12.2

loaded via a namespace (and not attached):
 [1] tidyselect_0.2.5 compiler_3.5.3   magrittr_1.5     assertthat_0.2.0 R6_2.2.2         tools_3.5.3      pillar_1.4.2    
 [8] glue_1.3.0       rstudioapi_0.7   dplyr_0.8.3      tibble_2.1.3     crayon_1.3.4     Rcpp_1.0.2       pkgconfig_2.0.2 
[15] rlang_0.4.0      purrr_0.2.5
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