I want a simple count of the number of subjects in each condition of a study. The data look something like this:

```
subjectid  cond   obser variable
1234        1        1      12   
1234        1        2      14
2143        2        1      19
3456        1        1      12 
3456        1        2      14 
3456        1        3      13   

etc       etc    etc       etc

```

This is a large dataset and it is not always obvious how many unique subjects contribute to each condition, etc. 

I have this in a data.frame.

What I want is something like

```
cond   ofSs 
1       122 
2        98

```

Where for each "condition" I get a count of the number of unique Ss contributing data to that condition. Seems like this should be painfully simple.