Number of "AT" repeats in sequence greater than 500bp

Question

[marija]

Hi, please I need your help.I have a sequence with length 1 000 000 bp. I want to create a function, which return the number of "AT" repeats (% A+T must be greater than 30%) and length must be greater than 500bp. I just don't know how to write the statement that the length must be greater than 500bp. Any help? Thank you

[Sean Davis]

Does letterFrequencyInSlidingView from the Biostrings Bioconductor package do what you need to get a summary of the data?

[marija]

I just know how to define that % A+T must be greater than 30%:

at <- function(x){
   alfreq <- alphabetFrequency(x, as.prob=TRUE)
    sum(alfreq[,c("A", "T")])
}

x > 0.30

[GenoMax]

Please edit the original post/question to add new information.

[cpad0112]

If you are parsing a single sequence for >500bp stretches with AT content > 30 % (i.e GC content <70), then what about window size and window overlap? or are you looking for set of sequences?

[marija]

I want the number of sequences that are greater than 500bp and have AT content > 30%. E.g in chr2:1,000,000-2,000,000 are 456 sequences with AT > 30% and length > 500bp (just example).