Subset with [ ] or subset( ) in R

Question

I was working with a dataframe similar to this one, called DB_reduced:

sex	BLT	BLN	BD
f	NA	45	2
f	3	46	NA
m	3.5	NA	1
f	4	43	1
NA	3.4	46	3
f	3.4	46	3
NA	3.6	41	3

I was expected to get a similar result with this two codes:

DB_reduced[DB_reduced$sex == "f", 2] # first line
# or
subset(DB_reduced, DB_reduced$Sexo == "f", select = 2, drop = TRUE) # second line

but rather than just finish with the same dataframe, the first returns:

sex  BLT
f    NA
f    3
f    4
NA   3.4
f    3.4
NA   3.5

and the second:

sex  BLT
f    NA
f    3
f    4
f    3.4

Why the difference? I thought that both codes worked in tha same way. How can I modify the first line to obtain the same result as the second?

Thanks all!

Answer 1

The documentation for ?subset specifies the following:

subset  logical expression indicating elements or rows to keep: missing values are taken as false.

so it drops NAs by default. You can get the same result using [ by adding & !is.na(DB_reduced$sex) as noted in the comments.