SQL-like functionality in R
I'm also more comfortable with SQL, but when working with large data sets in R, my favourite manipulation tool is the data.table package. Unlike sqldf, which lets you write SQL in R, data.table lets you write R in R - but gives you the ability to add indexes on data frames (well, data.tables, to be precise). The ability to index data frames makes 'joins' much much much faster. And being an R implementation, your code still looks like R.