Subsampling Fastq

[GenoMax]

Chayan: see this thread for other options in case the R solution does not work: http://seqanswers.com/forums/showthread.php?t=16505

[chayan]

i need to subsampling my fastq file of Iontorrent shotgun reads. I install R-2.15 and going by the previous suggesitios in this thread i tried to install ShortRead by > install.packages("ShortRead") but get the folowing error
Warning message:
In getDependencies(pkgs, dependencies, available, lib) :
package ‘Shortread’ is not available

ne help regarding this and if any other ways to random sampling of my fastq file. Thanx in advannce

Regards
Chayan

[westerman]

@shanebrubaker:

I suspect that you will get a better response if you ask your questing in a different thread with a title that contains "Digital Normalization" instead of burying it inside this thread. As for the answer to your question, I do not know. I am just starting to explore the program and may find out the answer later today.

[shanebrubaker]

On a related note, I was trying to reduce my data size by using khmer, from a paper on Digitial Normalization. Does anyone have experience with this tool? I am getting an error when using it where it says I have no paired reads ... but I do. Are there simliar tools?

[pbseq]

Hi chrisbala,
in ShortRead package ( manual :
http://www.bioconductor.org/packages.../ShortRead.pdf
)

there is writeFastq method that looks like what you need:
from manual:

writeFastq signature(object = "ShortReadQ", file = "character", mode="character",
...): Write object to file in fastq format. mode defaults to ‘w’. This creates a new
file, or fails if file already exists. Use mode="a" to append to an existing file. file is
expanded using path.expand.

hope it helps

[ewilbanks]

You can also use the mothur package which has a similar subsampling feature. The examples shows fasta only but I think it can handle paired fasta/qual files.

http://www.mothur.org/wiki/Sub.sample

[chrisbala]

exporting

Ok, followup question...

Once I've done

donkey <- FastqSampler(con, n=1e6, readerBlockSize=1e8, verbose=FALSE)

How do I write the sampled sequences to a fastq file?

THanks, and apologies if this obvious.

Chris

[chrisbala]

haha, I'm a bit of a newbie but not quite THAT bad...

I was testing it out on my Mac/GUI version of R. That does not seem to work.

Linux version seems fine. Maybe I'm still missing something ... but thats my guess as to what was going on.

Thanks though!

[Zigster]

i don't think you loaded ShortRead
start R

> R

in R:

> install.packages("ShortRead")
> library("ShortRead")
> ?FastqSampler

[chrisbala]

Anyone know an easy way to randomly subsample from a fastq (Illumina data)?

ShortReads seems to have a function FastqSampler, but I can't seem to make it work (?FastqSampler gives No documentation for 'FastqSampler' in specified packages and libraries:
you could try '??FastqSampler')

Thanks!

Chris