seqinr (version 4.2-36)

count: Composition of dimer/trimer/etc oligomers

Description

Counts the number of times dimer/trimer/etc oligomers occur in a sequence. Note that the oligomers are overlapping by default.

Usage

count(seq, wordsize, start = 0, by = 1,
 freq = FALSE, alphabet = s2c("acgt"), frame = start)

Value

This function returns a table whose dimnames are all the possible oligomers. All oligomers are returned, even if absent from the sequence.

Arguments

seq

a vector of single characters.

wordsize

an integer giving the size of word (n-mer) to count.

start

an integer (0, 1, 2,...) giving the starting position to consider in the sequence. The default value 0 means that we start at the first nucleotide in the sequence.

by

an integer defaulting to 1 for the window step.

freq

if TRUE, word relative frequencies (summing to 1) are returned instead of counts

alphabet

a vector of single characters used to build the oligomer set.

frame

synonymous for start

Author

D. Charif, J.R. Lobry with suggestions from Gabriel Valiente, Stefanie Hartmann and Christian Gautier

Details

count counts the occurence of all words by moving a window of length word. The window step is controlled by the argument by. start controls the starting position in the sequence for the count.

References

citation("seqinr")

See Also

table for the class of the returned objet. See rho and zscore for dinucleotide statistics.

Examples

a <- s2c("acgggtacggtcccatcgaa")
##
## To count dinucleotide occurrences in sequence a:
##
count(a, word = 2)
##
## To count trinucleotide occurrences in sequence a, with start = 2:
##
count(a, word = 3, start = 2)
##
## To count dinucleotide relative frequencies in sequence a:
##
count(a, word = 2, freq = TRUE)
##
## To count dinucleotides in codon positions III-I in a coding sequence:
##
alldinuclIIIpI <- s2c("NNaaNatNttNtgNgtNtcNctNtaNagNggNgcNcgNgaNacNccNcaNN")
resIIIpI <- count(alldinuclIIIpI, word = 2, start = 2, by = 3)
stopifnot(all( resIIIpI == 1))
##
## Simple sanity check:
##
#alldinucl <- "aattgtctaggcgacca"
#stopifnot(all(count(s2c(alldinucl), 2) == 1))
#alldiaa <- "aaxxzxbxvxyxwxtxsxpxfxmxkxlxixhxgxexqxcxdxnxrxazzbzvzyzwztzszpzfzmzkzlzizhzgzezqzczdznz
#rzabbvbybwbtbsbpbfbmbkblbibhbgbebqbcbdbnbrbavvyvwvtvsvpvfvmvkvlvivhvgvevqvcvdvnvrvayywytysypyfymyky
#lyiyhygyeyqycydynyryawwtwswpwfwmwkwlwiwhwgwewqwcwdwnwrwattstptftmtktltithtgtetqtctdtntrtasspsfsmsks
#lsishsgsesqscsdsnsrsappfpmpkplpiphpgpepqpcpdpnprpaffmfkflfifhfgfefqfcfdfnfrfammkmlmimhmgmemqmcmdmnm
#rmakklkikhkgkekqkckdknkrkallilhlglelqlcldlnlrlaiihigieiqicidiniriahhghehqhchdhnhrhaggegqgcgdgngrgae
#eqecedenereaqqcqdqnqrqaccdcncrcaddndrdannrnarra"
#stopifnot(all(count(s2c(alldiaa), 2, alphabet = s2c("arndcqeghilkmfpstwyvbzx")) == 1))
##
## Example with dinucleotide count in the complete Human mitochondrion genome:
##
humanMito <- read.fasta(file = system.file("sequences/humanMito.fasta", package = "seqinr"))
##
## Get the dinucleotide count:
##
dinu <- count(humanMito[[1]], 2)
##
## Put the results in a 4 X 4 array:
##
dinu2 <- dinu
dim(dinu2) <- c(4, 4)
nucl <- s2c("ACGT")
dimnames(dinu2) <- list(paste(nucl, "-3\'", sep = ""), paste("5\'-", nucl, sep = ""))
##
## Show that CpG and GpT dinucleotides are depleted:
##
mosaicplot(t(dinu2), shade = TRUE,
  main = "Dinucleotide XpY frequencies in the Human\nmitochondrion complete genome", 
  xlab = "First nucleotide: Xp", 
  ylab = "Second nucleotide: pY", las = 1, cex = 1)
mtext("Note the depletion in CpG and GpT dinucleotides", side = 1, line = 3)