Quickly remove zero variance variables from a data.frame

Question

I have a large data.frame that was generated by a process outside my control, which may or may not contain variables with zero variance (i.e. all the observations are the sa

Answer 1

How about using factor to count the number of unique elements and looping with sapply:

dat[sapply(dat, function(x) length(levels(factor(x)))>1)]
   B  D F
1  3 10 I
2  4 10 J
3  6 10 I
4  9 10 J
5  2 10 I
6  9 10 J
7  9 10 I
8  7 10 J
9  6 10 I
10 1  1 J

NAs are excluded by default, but this can be changed with the exclude parameter of factor:

dat[sapply(dat, function(x) length(levels(factor(x,exclude=NULL)))>1)]
   B  D F  G
1  3 10 I 10
2  4 10 J 10
3  6 10 I 10
4  9 10 J 10
5  2 10 I 10
6  9 10 J 10
7  9 10 I 10
8  7 10 J 10
9  6 10 I 10
10 1  1 J NA