Hi all,

I don't understand why I'm getting this error, when using ShortRead package' s FastqStreamerList function.

My code:

fql<-FastqStreamerList(c("a.fastq.gz", "b.fastq.gz"), n=1e6)
while(length(object <- yield(fql))) {
  writeFastq(object, "pooled.fastq.gz", "a", compress=TRUE)
}

Error in (function (classes, fdef, mtable)  :
  unable to find an inherited method for function ‘yield’ for signature ‘"FastqStreamerList"’

It says that "FastqStreamerList" its not inherited method for "yield" function whereas, in ShortRead's Vignette "FastqStreamerList" usage is described like this:

## FastqSampler and FastqStreamer
FastqSampler(con, n=1e6, readerBlockSize=1e8, verbose=FALSE,ordered = FALSE)
FastqSamplerList(..., n=1e6, readerBlockSize=1e8, verbose=FALSE,ordered = FALSE)
FastqStreamer(con, n, readerBlockSize=1e8, verbose=FALSE)
FastqStreamerList(..., n, readerBlockSize=1e8, verbose=FALSE)
yield(x, ...)

So where is the problem?

> sessionInfo()
R version 3.2.2 (2015-08-14)
Platform: x86_64-pc-linux-gnu (64-bit)
Running under: Ubuntu 14.04.3 LTS

locale:
 [1] LC_CTYPE=en_US.UTF-8       LC_NUMERIC=C               LC_TIME=lt_LT.UTF-8        LC_COLLATE=en_US.UTF-8    
 [5] LC_MONETARY=lt_LT.UTF-8    LC_MESSAGES=en_US.UTF-8    LC_PAPER=lt_LT.UTF-8       LC_NAME=C                 
 [9] LC_ADDRESS=C               LC_TELEPHONE=C             LC_MEASUREMENT=lt_LT.UTF-8 LC_IDENTIFICATION=C       

attached base packages:
[1] stats4    parallel  stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
 [1] ShortRead_1.26.0        GenomicAlignments_1.4.1 Rsamtools_1.20.4        GenomicRanges_1.20.5    GenomeInfoDb_1.4.2     
 [6] Biostrings_2.36.3       XVector_0.8.0           IRanges_2.2.7           S4Vectors_0.6.3         BiocParallel_1.2.20    
[11] BiocGenerics_0.14.0    

loaded via a namespace (and not attached):
 [1] lattice_0.20-33      bitops_1.0-6         grid_3.2.2           futile.options_1.0.0 zlibbioc_1.14.0      hwriter_1.3.2       
 [7] latticeExtra_0.6-26  futile.logger_1.4.1  RColorBrewer_1.1-2   lambda.r_1.1.7       tools_3.2.2          Biobase_2.28.0

I guess you mean the reference manual page ?FastqStreamerList rather than vignette. The manual page is documenting several functions together; it doesn't imply that all functions work with one another. You could write the while() loop as

fsl <- FastqStreamerList(c("a.fastq.gz", "b.fastq.gz"), n=1e6)

repeat {
    s1 = yield(fsl[[1]])
    if (length(s1) == 0)
        break
    s2 = yield(fsl[[2]])
    cat("lengths:", length(s1), length(s2), "\n")
}

I'm not sure what you want to do to create 'pooled', concatenate chunks with append(s1, s2). Or maybe you're trying to concatenate? Then something like

fsl <- FastqStreamerList(c("a.fastq.gz", "b.fastq.gz"), n=100)
for (i in seq_along(fsl)) {
    fs = fsl[[i]]
    repeat {
        s = yield(fs)
        if (length(s) == 0)
            break
        ## writeFastq(...)
    }
}