R Get minimum value in dataframe selecting rows on 2 columns [duplicate]

Question

I have a dataframe like the one I've simplified below. I want to first select rows with the same value based on column X, then in that selection select rows with the same value based on column Y. Then from that selection, I want to take the minimal value. I'm now using a forloop, but seems there must be an easier way. Thanks!

set.seed(123)    
data<-data.frame(X=rep(letters[1:3], each=8),Y=rep(c(1,2)),Z=sample(1:100, 12))
data
   X Y  Z
1  a 1 76
2  a 1 22
3  a 2 32
4  a 2 23
5  b 1 14
6  b 1 40
7  b 2 39
8  b 2 35
9  c 1 15
10 c 1 13
11 c 2 21
12 c 2 42

Desired outcome:

   X Y  Z
2  a 1 22
4  a 2 23
5  b 1 14
8  b 2 35
10 c 1 13
11 c 2 21

Answer 1

Here is a data.table solution:

library(data.table)
data = data.table(data)
data[, min(Z), by=c("X", "Y")]

EDIT based on OP's comment:

If there is a NA value in one of the columns we sort by, an additional row is created:

data[2,2] <-NA
data[, min(Z,na.rm = T), by=c("X", "Y")]

   X  Y V1
1: a  1 31
2: a NA 79
3: a  2 14
4: b  1 31
5: b  2 14
6: c  1 50
7: c  2 25