Question

My dataframe looks like this:

ID | value 1 | value 2 | value 3 | value 4
1  |    M    |    D    |    F    |   A
2  |    F    |    M    |    G    |   B
3  |    M    |    D    |    F    |   A
4  |    L    |    D    |    E    |   B

I want to get something like this.

value 1 | value 2 | value 3 | value 4|  Number of combinations
  M     |    D    |    F    |   A    |     2
  F     |    M    |    G    |   B    |     1
  L     |    D    |    E    |   B    |     1

e.g. to count the number of unique combinations of the columns value 1 – value 4.

Answer 1

count in plyr package will do that task.

> df
  ID   value.1   value.2   value.3 value.4
1  1     M         D         F           A
2  2     F         M         G           B
3  3     M         D         F           A
4  4     L         D         E           B
> library(plyr)
> count(df[, -1])
    value.1   value.2   value.3 value.4 freq
1     F         M         G           B    1
2     L         D         E           B    1
3     M         D         F           A    2