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  • swbarnes2
    replied
    Originally posted by Ben Langmead View Post
    Hi swbarnes2 - I'm going to add your suggestion to the sourceforge feature request list. You seem invested in SOAP-style alignment, but I would note that Maq-style (the default) accomplishes something like iterative trimming by simply discounting the penalty associated with mismatches at low-quality positions (usually clustered at the 3' end).
    Yes, I did notice that, (and I'm running pretty close to default:--best -p 4 -t) but I still see about the same number of aligned reads as I do with SOAP set to no trimming. SOAP iteratively trimming yields a whole lot more. By a test I ran last night, allowing SOAP to iteratively trim every base pair until there were no more than 2 mismatches yielded an extra million reads aligning in one lane compared to bowtie. During the day, I run the faster 'trim 8 bp at a time', but the difference is still substantial.

    Out of curiosity, do you use SOAP's mode for aligning with indels?
    Yes, that's part of the reason. Maq's indel detection is pretty hopeless, or it was when I looked at it last. And I think that it was not handling repeats at all, but maybe I'm misremembering.

    I've tried Maq, and I use it as a compliment to SOAP, but I didn't like that the output was all processed for me. I wanted to see qualities and repetitiveness and read IDs and pair distances across the genome, and the pile-up view doesn't show that, and I'm pretty sure that Maqview won't either. But the output of Maq didn't give me the raw alignment info to construct a file with all that info, so I use SOAP, and process that output.

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  • Ben Langmead
    replied
    Hi swbarnes2 - I'm going to add your suggestion to the sourceforge feature request list. You seem invested in SOAP-style alignment, but I would note that Maq-style (the default) accomplishes something like iterative trimming by simply discounting the penalty associated with mismatches at low-quality positions (usually clustered at the 3' end).

    Out of curiosity, do you use SOAP's mode for aligning with indels?

    Leave a comment:


  • swbarnes2
    replied
    But I don't want to trim accurate bases needlessly. The virture of iterative trimming is that it only trims as many as it needs.

    I could run the program a bunch of times with different trimming, and recombine the data after, but that's a pain, and might not be as efficient as having the program trim each read as it is handling it.

    Leave a comment:


  • Chipper
    replied
    It has an option already to trim before alignment (-3 / -5) so why not try with that. It would help though if the unaligned reads were saved separately.

    Leave a comment:


  • swbarnes2
    replied
    Could Bowtie be altered to have an interative trimming function, like SOAP has? I just did a quick comparison, and while untrimmed SOAP and Bowtie had about the same number of aligned reads with no trimming, (and Bowtie was much faster) I find that iteratively trimming the last bases with SOAP, 8 at a time, gives a huge boost to the number of reads that align, up to 30%.

    Leave a comment:

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