filterFastq: Filter fastq from one file to another
In ShortRead: FASTQ input and manipulation

Description Usage Arguments Author(s) Examples

filterFastq filters reads from source to destination file(s) applying a filter to reads in each file. The filter can be a function or FilterRules instance; operations are done in a memory-efficient manner.

1 2	filterFastq(files, destinations, ..., filter = FilterRules(), compress=TRUE, yieldSize = 1000000L)

`files`	a character vector of valid file paths.
`destinations`	a character vector of destinations, recycled to be the same length as `files`. `destinations` must not already exist.
`...`	Additional arguments, perhaps used by a `filter` function.
`filter`	A simple function taking as it's first argument a `ShortReadQ` instance and returning a modified `ShortReadQ` instance (e.g., with records or nucleotides removed), or a `FilterRules` instance specifying which records are to be removed.
`compress`	A logical(1) indicating whether the file should be gz-compressed. The default is `TRUE`.
`yieldSize`	Number of fastq records processed in each call to `filter`; increase this for (marginally) more efficient I/O at the expense of increased memory use.

Martin Morgan mtmorgan@fhcrc.org

## path to a convenient fastq file
sp <- SolexaPath(system.file('extdata', package='ShortRead'))
fl <- file.path(analysisPath(sp), "s_1_sequence.txt")

## filter reads to keep those with GC < 0.7
fun <- function(x) {
    gc <- alphabetFrequency(sread(x), baseOnly=TRUE)[,c("G", "C")]
    x[rowSums(gc) / width(x) < .7]    
}
filterFastq(fl, tempfile(), filter=fun)

## trimEnds,character-method uses filterFastq internally
trimEnds(fl, "V", destinations=tempfile())