String Processing

 > a=c("AA","V")
 > a[0]
 character(0)

 > a[-1]
 [1] "V"
 > a[-2]
 [1] "AA"
 > a[-3]
 [1] "AA" "V"

 > seq = "atGCTGGATGAGaGCGAaaGAGCAGAGAGCCA"
 > toupper(seq)
 [1] "ATGCTGGATGAGAGCGAAAGAGCAGAGAGCCA"
 > tolower(seq)
 [1] "atgctggatgagagcgaaagagcagagagcca"

 > seq=toupper(seq)
 > substr(seq, start = 1, stop = 3)
 [1] "ATG"

 > x <-"AAA"
 > x
 [1] "AAA"
 > y <- "BBB"
 > c(x,y)
 [1] "AAA" "BBB"
 > paste(x,y)
 [1] "AAA BBB"
 > paste(x,y,sep="")
 [1] "AAABBB"

 > x=c("Orange","Apple","Banana")
 > min(x)
 [1] "Apple"
 > max(x)
 [1] "Orange"
 > sort(x)
 [1] "Apple"  "Banana" "Orange"

 > x=c("A","T","A","G","C","A","A","T")
 > summary(x)
    Length     Class      Mode
         8 character character
 > y=factor(x)
 > summary(y)
 A C G T
 4 1 1 2
 > y[0]
 factor(0)
 Levels: A C G T