Selecting rows that are the same in separate data frames

I want to compare two matrices or data frames and select or get an index
for those rows which are the same in both. I have tried the following :






a = matrix ( 1:10, ncol = 2 )
a

b = matrix ( c ( 2,3,4,7,8,9 ), ncol = 2 )
b

a[a==b]






a = as.data.frame ( matrix ( 1:10, ncol = 2 ) )
a

b = as.data.frame ( matrix ( c ( 2,3,4,7,8,9 ), ncol = 2 ) )
b

a[a==b]








Any ideas please.


Thanks.


Simon Parker
Imperial College