Strange behavior for filtering in data.table with NA values

[sergiizaskaleta]

Reported from this SO question:
I've stumbled upon weird data table i behavior that returns a row with NAs where I would expect an empty data table. See:

a = data.table(a = 1, d = NA) 
a[!is.na(a) & d == "3"] 
#     a  d
#1: NA NA

I would expect an empty data table as a result here.
Compare to:

a = data.table(a = c(1,2), d = c(NA,3))
a[!is.na(a) & d == "3"] 
#    a d
#1: 2 3

This one does not produce an extra row with NA values, though.

> sessionInfo()
# R version 2.15.2 (2012-10-26)
# Platform: x86_64-w64-mingw32/x64 (64-bit)
# 
# locale:
# [1] LC_COLLATE=English_United Kingdom.1252 
# [2] LC_CTYPE=English_United Kingdom.1252
# 
# [3] LC_MONETARY=English_United Kingdom.1252
# [4] LC_NUMERIC=C
# 
# [5] LC_TIME=English_United Kingdom.1252
# 
# attached base packages:
# [1] stats graphics grDevices utils datasets methods base

[mattdowle]

Many thanks.
Did you really mean to include !is.na(a) i.e. on a column which has no NA?
i.e. instead of :

a = data.table(a = c(1,2), d = c(NA,3))
a[!is.na(a) & d == "3"]

this seems sufficient to demonstrate :

a = data.table(a = c(1,2), d = c(NA,3))
a[d == 3]

Indeed seems like there could be a bug here with 1-row data.table's containing one NA.

[sergiizaskaleta]

This actually was used in a piece of code that worked per subsets of a data.table, and in some rare subset case there could be such a scenario.

[arunsrinivasan]

Quite tightly linked to #857 IMO. Would push this to 1.9.8..

[arunsrinivasan]

Fixed with this commit: 353cf8a

Marked the wrong issue name while committing.

[mattdowle]

Causing package treemap to fail. Investigating.