Getting unique rows of a table and their numbers

Question

I have a dataframe:

id  y   z
oX  79  100
oX  23  46
oX  10  29
uM  12  90
uT  43  50
uT  13  99

I would like to keeep unique rows based on

Answer 1

Just wanted to post another alternative, consider data.table

> library(data.table)
> data.table(mydf)[,.N, by="id"]
   id N
1: oX 3
2: uM 1
3: uT 2