optimized by group gvar() returns error: "negative length vectors are not allowed" when within-group variance is 0

[osofr]

Using latest development version of data.table (1.10.5):

This returns an error:

library(data.table)
testDT <- data.table(col1 = c(1,1,1, 2,2,2), col2 = c(2,2,2,1,1,1), ID = c(rep(1,3), rep(2,3)))
setkeyv(testDT, "ID")
testDT[, lapply(.SD, var), by = ID]

Error in gvar(col1) : negative length vectors are not allowed

This however works fine:

testDT[, lapply(.SD, stats::var), by = ID]
   ID col1 col2
1:  1    0    0
2:  2    0    0

[franknarf1]

Fwiw , no repro with

data.table 1.10.5 IN DEVELOPMENT built 2017-04-04 00:37:37 UTC; travis
 
R version 3.3.3 (2017-03-06)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows 10 x64 (build 14393)

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

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

other attached packages:
[1] data.table_1.10.5

loaded via a namespace (and not attached):
[1] tools_3.3.3

[osofr]

Apologies, adding session details, Mac OS X, R 3.3.1.

R version 3.3.1 (2016-06-21) -- "Bug in Your Hair"
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> library(data.table)
data.table 1.10.5 IN DEVELOPMENT built 2017-04-04 00:37:37 UTC; travis
  The fastest way to learn (by data.table authors): https://www.datacamp.com/courses/data-analysis-the-data-table-way
  Documentation: ?data.table, example(data.table) and browseVignettes("data.table")
  Release notes, videos and slides: http://r-datatable.com
> testDT <- data.table(col1 = c(1,1,1, 2,2,2), col2 = c(2,2,2,1,1,1), ID = c(rep(1,3), rep(2,3)))
> setkeyv(testDT, "ID")
> testDT[, lapply(.SD, var), by = ID]
Error in gvar(col1) : negative length vectors are not allowed
> testDT[, lapply(.SD, stats::var), by = ID]
   ID col1 col2
1:  1    0    0
2:  2    0    0
> 

[MichaelChirico]

Linking this knitr issue I created which may be related (though it seems to be a knitr issue in my case):

yihui/knitr#1457