[R] Help searching a matrix for only certain records

[arun]

Hi,
Try this:
set.seed(51)
 mat1<- as.matrix(data.frame(REC.TYPE= sample(c("SAO","FAO","FL-1","FL-2","FL-15"),20,replace=TRUE),Col2=rnorm(20),Col3=runif(20),stringsAsFactors=FALSE))
 dat1<- as.data.frame(mat1,stringsAsFactors=FALSE)

dat1[grepl("SAO|FL-15",dat1$REC.TYPE),]
#   REC.TYPE        Col2       Col3
#4     FL-15 -1.31594143 0.41193183
#6     FL-15  0.43419586 0.96004780
#9     FL-15 -0.90690732 0.84000657
#10      SAO  0.21363265 0.20155142
#13      SAO -0.55566727 0.71606558
#15      SAO -0.71533068 0.90851364
#17      SAO  1.58611036 0.97475674
#20      SAO -0.42904914 0.33710578
A.K.



----- Original Message -----
From: Matt Borkowski <mathias1979 at yahoo.com>
To: r-help at r-project.org
Cc: 
Sent: Sunday, March 3, 2013 1:11 AM
Subject: [R] Help searching a matrix for only certain records

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

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