snpMatrix (version 1.19.24)

read.HapMap.data: function to import HapMap genotype data as snp.matrix

Description

Given a URL for HapMap genotype data, read.HapMap.data, download and convert the genotype data into a snp.matrix class object, and saving snp support infomation into an associated data.frame.

Usage

read.HapMap.data(url, verbose=FALSE, save=NULL, ...)

Arguments

url

URL for HapMap data. Web data is to be specified with prefix "http://", ftp data with prefix "ftp://", and local file as "file://"

verbose

Where the dnSNPalleles annotation is ambiguous, output more details information about how/why assignment is made. See Notes below.

save

filename to save the download - if unspecified, a temporary file will be created but removed afterwards.

...

Place-holder for further switches - currently ignored.

Value

• Returns a list containing these two items when successful, otherwise returns NULL:
• snp.data
  A snp.matrix-class object containing the snp data
• snp.support
  A data.frame, containing the dbSNPalleles, Chromosome, Position, Strand entries from the hapmap genotype file, together with the actual Assignment used for allele 1 and allele 2 during the conversion (See Details above and Note below).

Details

During the conversion, if the dbSNPAlleles entry is exactly of the form "X/Y", where X, Y = A or C or G or T, then it is used directly for assigning allele 1 and allele 2.

However, about 1 in 1000 entries are more complicated e.g. may involving deletion, e.g. "-/A/G" or "-/A/AGT/G/T". Some heuristics are used in such cases, in which the observed genotypes in the specific snp of the current batch are examined in two passes. The first time to see which bases are present, excluding "N".

If more than 2 bases are observed in the batch specified in the url, the routine aborts, but so far this possibility has not arisen in tests. If there is exactly two, then allele 1 and 2 are assigned in alphabatical order (dbSNPAlleles entries seems to be always in dictionary order, so the assignment made should agree with a shorten version of the dbSNPAlleles entry). Likewise, if only "A" or "T" is observed, then we know automatically it is the first (assigned as "A/.") or the last allele (assigned as "./T") of a hypothetical pair, without looking at the dbSNPAlleles entry. For other observed cases of 1 base, the routine goes further and look at the dnSNPAlleles entry and see if it begins with "-/X/" or ends with "/X", as a single base, and compare it with the single base observed to see if it should be allele 1 (same as the beginning, or different from the end) and allele 2 (same as the end, or different from the beginning). If no decision can be made for a particular snp entry, the routine aborts with an appropriate message. (for zero observed bases, assignment is "./.", and of course, all observed genotypes of that snp are therefore converted to the equivalent of NA)

(This heuristics does not cover all grounds, but practically it seems to work. See Notes below.)

References

http://www.hapmap.org/genotypes

See Also

snp.matrix-class

Examples

## ** Please be aware that the HapMap project generates new builds from
## ** to time and the build number in the URL changes.

> library(snpMatrix)
> testurl <- "http://www.hapmap.org/genotypes/latest/fwd_strand/non-redundant/genotypes_chr1_CEU_r21_nr_fwd.txt.gz"
> result1 <- read.HapMap.data(testurl)
> sum1 <- summary(result1$snp.data)

> head(sum1[is.finite(sum1$z.HWE),], n=10)
           Calls Call.rate         MAF      P.AA       P.AB      P.BB      z.HWE
rs1933024     87 0.9666667 0.005747126 0.0000000 0.01149425 0.9885057 0.05391549
rs11497407    89 0.9888889 0.005617978 0.0000000 0.01123596 0.9887640 0.05329933
rs12565286    88 0.9777778 0.056818182 0.0000000 0.11363636 0.8863636 0.56511033
rs11804171    83 0.9222222 0.030120482 0.0000000 0.06024096 0.9397590 0.28293272
rs2977656     90 1.0000000 0.005555556 0.9888889 0.01111111 0.0000000 0.05299907
rs12138618    89 0.9888889 0.050561798 0.0000000 0.10112360 0.8988764 0.50240136
rs3094315     88 0.9777778 0.136363636 0.7272727 0.27272727 0.0000000 1.48118392
rs17160906    89 0.9888889 0.106741573 0.0000000 0.21348315 0.7865169 1.12733108
rs2519016     85 0.9444444 0.047058824 0.0000000 0.09411765 0.9058824 0.45528615
rs12562034    90 1.0000000 0.088888889 0.0000000 0.17777778 0.8222222 0.92554468

## ** Please be aware that the HapMap project generates new builds from
## ** to time and the build number in the URL changes.

## This URL is broken up into two to fit the width of
## the paper. There is no need in actual usage:
> testurl2 <- paste("http://www.hapmap.org/genotypes/latest/",
                  "fwd_strand/non-redundant/genotypes_chr1_JPT_r21_nr_fwd.txt.gz", sep="")
> result2 <- read.HapMap.data(testurl2)

> head(result2$snp.support)
           dbSNPalleles Assignment Chromosome Position Strand
rs10399749          C/T        C/T       chr1    45162      +
rs2949420           A/T        A/T       chr1    45257      +
rs4030303           A/G        A/G       chr1    72434      +
rs4030300           A/C        A/C       chr1    72515      +
rs3855952           A/G        A/G       chr1    77689      +
rs940550            C/T        C/T       chr1    78032      +