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Standardise GWAS

standardise_gwas.Rmd

Here is a simple example of using the genepi.utils::GWAS() object to standardise your GWAS input ready for use with other features in this package. First some unprocessed example data:

library(genepi.utils)

filepath <- system.file("extdata", "example2_gwas_sumstats.tsv", package="genepi.utils")

gwas <- data.table::fread(filepath)

gwas

Column mapping

A number of column mapping options for standard GWAS formats are provided through the ColumnMap() class.

  • a string - valid id for a pre-defined map (e.g. ‘giant’ or ‘gwama’)
  • an unnamed character vector or list - the constructor will create a ColumnMap object as long as the provided column names are found within the list of known aliases
  • a named character vector or list - the names must be the standard column names to map to, and the values the current column names
  • a list of Column class objects 
# possible inputs to mapping object
colmap_input1 <-    c('MARKER', 'CHR', 'POS', 'BETA', 'SE', 'P', 'EAF', 'A1', 'A2') # will try to guess standard name mapping
colmap_input2 <- list(rsid='MARKER', chr='CHR', bp='POS', beta='BETA', se='SE', p='P', eaf='EAF', ea='A1', oa='A2') # standard naming
colmap_input3 <- list(Column(name='rsid', alias=c('MARKER'), type='character'),
                      Column(name='chr',  alias=c('CHR'),    type='character'),
                      Column(name='bp',   alias=c('POS'),    type='integer'),
                      Column(name='beta', alias=c('BETA'),   type='numeric'),
                      Column(name='se',   alias=c('SE'),     type='numeric'),
                      Column(name='p',    alias=c('P'),      type='numeric'),
                      Column(name='eaf',  alias=c('EAF'),    type='numeric'),
                      Column(name='ea',   alias=c('A1'),     type='character'),
                      Column(name='oa',   alias=c('A2'),     type='character'))

# column mapping object
map <- ColumnMap("ns_map")
map <- ColumnMap(colmap_input1)
map <- ColumnMap(colmap_input2)
map <- ColumnMap(colmap_input3)

map

Standardise GWAS

A GWAS can then be standardised like so:

filepath <- system.file("extdata", "example2_gwas_sumstats.tsv", package="genepi.utils")

gwas <- GWAS(dat=filepath, map=map)

gwas

As data.table

A GWAS object can be easily converted to data.table.

g <- as.data.table(gwas)

g

Custom quality control

A GWAS object is created after a number of data checks and filters. The default filters can be altered via the filters argument, which takes a named list of strings that can be evaluated as expressions to filter a data.table. The results of the filtering can be found in the @qc property of the GWAS object which is a named list of integer vectors identifying rows that fail that particular filter.

gwas <- data.table::fread(filepath)

gwas <- GWAS(dat     = gwas, 
             map     = map, 
             filters = list(beta_invalid = "!is.infinite(beta) & abs(beta) < 10",
                            eaf_invalid  = "eaf >= 0.01 & eaf <= 0.99",
                            p_invalid    = "!is.infinite(p) & sign(p) != -1 & p < 1",
                            se_invalid   = "!is.infinite(se) & abs(se) < 10",
                            chr_missing  = "!is.na(chr)",
                            bp_missing   = "!is.na(bp)",
                            beta_missing = "!is.na(beta)",
                            se_missing   = "!is.na(se)",
                            p_missing    = "!is.na(p)",
                            eaf_missing  = "!is.na(eaf)"))

gwas@qc