README.md

In vsbuffalo/tasselr: S4 methods for working with HDF5 files from TASSEL

tasselr

Tassel outputs HDF5 files full of GBS genotyping data. This package is an R interface to a subset of the information in these files, so users can quickly load and work with these data.

Required Packages

From CRAN:

• methods
• Rcpp

From Bioconductor:

• GenomicRanges
• Biobase
• rhdf5

Install these packages, then using devtools (which you can install via CRAN), do:

install_github("vsbuffalo/tasselr")

Loading Tassel HDF5 GBS into R

First, we initialize the HDF5 file with initTasselHDF5. By default, initTasselHDF5() assumes the HDF5 file is in Tassel5's schema; set the version='4' to change this. initTasselHDF5() loads in the loci positions as a GRanges object, and stores reference and alternate alleles (which you can access with the ref and alt accessor functions, respectively):

> gbs <- initTasselHDF5("path/to/mygbs.h5")
> gbs
    Tassel HDF5 object at 'path/to/mygbs.h5'
    955690 loci x 2060 samples
    Number of chromosomes: 11
    Object size: 127.022 Mb

> head(alt(gbs), 20)
  3   4   5   6   8  11  13  14  15  17  18
 "T" "A" "C" "G" "T" "C" "T" "T" "G" "G" "T"   [...]

> head(ref(gbs))
[1] "C" "C" "C" "C" "C" "A"

Loading Genotypes

Genotypes are loaded and decoded into the number of alternate alleles they have (0, 1, 2) for biallelic loci by the method loadBiallelicGenotypes():

> gbs <- loadBiallelicGenotypes(gbs)

The conversion methods are written in C++ with Rcpp so they're fast-ish.

The accessor function geno() can be used to extract this genotype matrix. Note that the number of loci, and the reference and alternate alleles will change, as only biallelic loci are kept. The object will always have internal consistency, and you should always use accessor functions to access data in slots.

Accessor functions:

• granges(): for loci positions.
• alt(): for alternate alleles.
• ref(): for reference alleles.
• geno(): for genotype matrix.

Warnings

• This is tied to Tassel's HDF5 formats (Tassel 4 and 5 only). If these change, there are no guarantees the data loaded in will be correct (sorry). Always run a sanity checks!

Todo

• Lazier loading, e.g. of specific samples or chromosomes at a time through reading in specific sample datasets or subsets.

• Interface to the /depth datasets, which contain a lot of information.

• Possibly re-looking into storing genotyping data using R's raw atomic vector, which will use 1/4 of the memory.

• Apply functions, which load parts from HDF5 files only as needed and apply function on them, e.g. functions for taking coverage depth statistics.

Dev Notes

• Initially I used R to find and convert missing values 0xFF values into NAs. This took 261.093 seconds (261.093 user, 129.891 system, 454.579 elapsed). Now this is done in C++ and it takes about 189.709 seconds (189.709 user, 59.941 system, 290.936 elapsed).

• Initially I used Rcpp to encode genotypes from tasselr. However, Rcpp's IntegerMatrix doesn't support matrices that are larger than 2^31 - 1 elements. To remedy this, I wrote everything in C and used a do.call().

vsbuffalo/tasselr documentation built on May 3, 2019, 7:08 p.m.