[R] Selecting groups with R

[Michael A. Miller]

To drop empty factor levels from a subset, I use the following:

a.subset <- subset(dataset, Color!='BLUE')
ifac <- sapply(a.subset,is.factor)
a.subset[ifac] <- lapply(a.subset[ifac],factor)

Mike


> dataset
  Color Score
1   RED    10
2   RED    13
3   RED    12
4 WHITE    22
5 WHITE    27
6 WHITE    25
7  BLUE    18
8  BLUE    17
9  BLUE    16
> table(dataset)
       Score
Color   10 12 13 16 17 18 22 25 27
  BLUE   0  0  0  1  1  1  0  0  0
  RED    1  1  1  0  0  0  0  0  0
  WHITE  0  0  0  0  0  0  1  1  1
> 
> a.subset <- subset(dataset, Color!='BLUE')
> a.subset
  Color Score
1   RED    10
2   RED    13
3   RED    12
4 WHITE    22
5 WHITE    27
6 WHITE    25
> 
> table(a.subset)
       Score
Color   10 12 13 22 25 27
  BLUE   0  0  0  0  0  0
  RED    1  1  1  0  0  0
  WHITE  0  0  0  1  1  1
> 
> ifac <- sapply(a.subset,is.factor)
> a.subset[ifac] <- lapply(a.subset[ifac],factor)
> 
> table(a.subset)
       Score
Color   10 12 13 22 25 27
  RED    1  1  1  0  0  0
  WHITE  0  0  0  1  1  1