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Testing code snippets.

I’m just writing this to see how code snippets work using markdown and jekyll…

Here is a simple thing I often do to summarize distributions of pieces of information from the INFO field of a vcf file…

cl <- "tabix my.vcf.bgz Scaffold10 | grep -oP '(?<=DP=)[^;]+'"
dp <- scan(pipe(cl))

Here I’ve extracted the contents of the tag ‘DP’, which contains the depth of coverage of the variant.

In this case I’m feeding a line of code to the system, “cl”, with pipe(), and reading the results into R with scan().

To break down “cl”: I use tabix to quickly access arbitrary chunks of VCF files, then pipe the output to grep to pull out the depth. The flag -o extracts the regex match, and -P allows me to use what’s called a ‘positive lookahead’. That’s the section (?<=DP=). This requires the regex to match “DP=”, but doesn’t return it as part of the match. Then I match the characters in the field with [^;]+, which matches one or more of any character except “;”, which is the field delimiter.

Here’s the result: