Remove constant columns with or without NAs

Question

I am trying to get many lm models work in a function and I need to automatically drop constant columns from my data.table. Thus, I want to keep only columns wit

Answer 1

Just change

all(is.na(.col)) || all(.col[1L] == .col)

to

all(is.na(.col) | .col[1L] == .col)

Final code:

same <- sapply( df, function(.col){ all( is.na(.col) | .col[1L] == .col ) } )
df1 <- df[,!same, with=F]

Result:

    x
1:  1
2:  2
3:  3
4: NA
5:  5