Expand and grouping variables

[danielsjf]

It looks like expand, combined with some grouping variables gives some strange results:

> df <- data.frame(a=1:2,b=3:4,c=5:6)
> df %>% expand(a,b,c)
Source: local data frame [8 x 3]
      a     b     c
  (int) (int) (int)
1     1     3     5
2     1     3     6
3     1     4     5
4     1     4     6
5     2     3     5
6     2     3     6
7     2     4     5
8     2     4     6
> df %>% group_by(a,b) %>% expand(a,b,c)
Source: local data frame [8 x 7]
      b     a     a     b     a     b     c
  (int) (int) (int) (int) (int) (int) (int)
1     3     1     1     3     1     3     5
2     3     1     1     3     2     4     6
3     3     1     2     4     1     3     5
4     3     1     2     4     2     4     6
5     4     2     1     3     1     3     5
6     4     2     1     3     2     4     6
7     4     2     2     4     1     3     5
8     4     2     2     4     2     4     6