[R] Help searching a matrix for only certain records

[Matt Borkowski]

Let me start by saying I am rather new to R and generally consider myself to be a novice programmer...so don't assume I know what I'm doing :)

I have a large matrix, approximately 300,000 x 14. It's essentially a 20-year dataset of 15-minute data. However, I only need the rows where the column I've named REC.TYPE contains the string "SAO  " or "FL-15". 

My horribly inefficient solution was to search the matrix row by row, test the REC.TYPE column and essentially delete the row if it did not match my criteria. Essentially...

> j <- 1
> for (i in 1:nrow(dataset)) {
>    if(dataset$REC.TYPE[j] != "SAO  " && dataset$RECTYPE[j] != "FL-15") {
>      dataset <- dataset[-j,]  }
>    else {
>      j <- j+1  }
> }

After watching my code get through only about 10% of the matrix in an hour and slowing with every row...I figure there must be a more efficient way of pulling out only the records I need...especially when I need to repeat this for another 8 datasets. 

Can anyone point me in the right direction?

Thanks!

Matt