.SD locked error when creating variable after subsetting data with .SD in j

[marc-outins]

Creating a new variable in a data.table which was created from an existing data.table using .SD in j gives a .SD locked error if i is supplied but no error if i is not supplied.

dt <- data.table(a = 1:10)

# Works as expected
sub_dt <- dt[,.SD]
sub_dt[,b := 1]

# Gives .SD is locked error
sub_dt2 <- dt[a == 5,.SD]
sub_dt2[,b := 1]

The address for .SD and sub_dt2 are the same.

# prints address and returns value
printSDaddr <-function(x){
  print(address(x))
  x
}

# Address of .SD and sub_dt are different
sub_dt <- dt[,printSDaddr(.SD)]
address(sub_dt)

# Address of .SD and sub_dt2 are the same
sub_dt2 <- dt[a == 5,printSDaddr(.SD)]
address(sub_dt2)

R version 3.1.3 (2015-03-09)
Platform: x86_64-w64-mingw32/x64 (64-bit)
Running under: Windows Server 2008 R2 x64 (build 7601) Service Pack 1

locale:
[1] LC_COLLATE=English_United States.1252  LC_CTYPE=English_United States.1252   
[3] LC_MONETARY=English_United States.1252 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] setlr_0.1           data.table_1.9.5    XLConnect_0.2-11    XLConnectJars_0.2-9

loaded via a namespace (and not attached):
 [1] chron_2.3-47     codetools_0.2-11 curl_0.9.2       devtools_1.8.0   digest_0.6.8     foreach_1.4.2   
 [7] git2r_0.10.1     httr_1.0.0       iterators_1.0.7  knitr_1.10.5     magrittr_1.5     memoise_0.2.1   
[13] plyr_1.8.3       R6_2.1.1         Rcpp_0.12.0      reshape2_1.4.1   rJava_0.9-6      rversions_1.0.1 
[19] stringi_0.4-1    stringr_1.0.0    tools_3.1.3      xml2_0.1.1 

[jangorecki]

Please read Support wiki before posting.
Looks like a bug where .data.table.locked attribute is not removed on sub_dt2 <- dt[a == 5,.SD] call, confirmed on latest version.

sub_dt2 <- dt[a == 5,.SD]
str(sub_dt2)
# Classes ‘data.table’ and 'data.frame':    1 obs. of  1 variable:
# $ a: int 5
#  - attr(*, ".data.table.locked")= logi TRUE