[R] Finding rows common to two datasets

[Steve Murray]

Dear all,
 
I have 2 data frames, both with 14 columns of data and differing numbers of rows. The first two columns are 'Latitude' and 'Longitude'. I want to find the pairs of Latitude and Longitude coordinates which are common to both datasets, and output a new data frame which is composed of these coincident rows. I tried using the 'unique' command, but had difficulties interpreting the help file.
 
Many thanks for any help offered,
 
Steve