 I have a list of genomic ranges mapped to hg19 . my data is in matrix format lets call it  `ranges` which has 600,000 rows and 4 clumns 
here is few row of my data

     head(ranges)
      chr    start    end      strand
    [1,] "chr1" "10025"  "10525"  "."   
    [2,] "chr1" "13252"  "13752"  "."   
    [3,] "chr1" "16019"  "16519"  "."   
    [4,] "chr1" "96376"  "96876"  "."   
    [5,] "chr1" "115440" "115940" "."   
    [6,] "chr1" "235393" "235893" "."   
Is there a function that gets sequences and calculates GC content for each row( each range)
I would prefer that  output be in a vector format
I would really appreciate your help




thank you all, 
these solutions are great.
 I also found a function that calculates GC content using BSgenome.Hsapiens.UCSC.hg19.

    require(BSgenome.Hsapiens.UCSC.hg19)
    require(BSgenome)
    library(Repitools)
    Granges<- makeGRangesFromDataFrame(data.frame(ranges))
    gc<- gcContentCalc(Granges , organism=Hsapiens, verbose=TRUE)

