Sorry if the description is vague - I'm extremely new to R and finding it hard to visualise exactly what I want to do. Suppose I have some data:

```
dat <- read.table(text = '
A    B    C
"Mike"    1    1
"Mike"    1    17
"Mike"    1    3
"Mike"    2    4
"Mike"    3    18
"Simon"    1    2
"Simon"    1    25
"Simon"    2    12
"Simon"    2    182
"Simon"    2    6', header=TRUE)
... etc.

```

Suppose I want to know the number of names (A column) that have 3 entries where B = 1, and the number of names that have 3 entries where B = 2, and so on?

In the example above, "Mike" has 3 entries where B = 1, but not B = 2 or B = 3. "Simon" has 3 entries for B = 2, and so on. It's crossing entries in the data, which I've not done yet in R, and I'm not sure how best to approach it.