Possible Duplicate:
Select only the first rows for each unique value of a column in R

I have a matrix of the following form:

col1 col2

1    2   
1    2    
1    2   
1    2   
1    2
2    5
2    5
2    5
3    7
3    7
3    7
3    7
3    7
3    7
3    7
3    7
4    2 
4    2 
4    2

I would like to select all the unique rows based on ‘col1’.

which in this case would be the first row from each unique value in col1:

subset:

col1   col2
1      2 
2      5
3      7
4      2

Here’s what I’ve tried:

https://dl.dropbox.com/u/22681355/matrix.csv
mat<-read.csv("matrix.csv")
sub<-unique(mat$V1)
subset(mat, mat==c(sub)

It spits out much more than I would expect to get and I get this error mesage:

Warning message:
In contacts$V1 == c(g) :
longer object length is not a multiple of shorter object length