fst_wh: The Weir-Hill FST estimator

In OchoaLab/popkinsuppl: Supplement to popkin package

The Weir-Hill FST estimator

Description

This function implements the full FST estimator from Weir and Hill (2002) (equation 9). Handles very large data, passed as BEDMatrix or as a regular R matrix. Handles missing values correctly.

Usage

fst_wh(
  X,
  labs,
  m = NA,
  ind_keep = NULL,
  loci_on_cols = FALSE,
  mem_factor = 0.7,
  mem_lim = NA,
  m_chunk_max = 1000
)

Arguments

X	The genotype matrix (BEDMatrix, regular R matrix, or function, same as popkin).
labs	A vector of subpopulation assignments for every individual. At least two subpoplations must be present.
m	The number of loci, required if X is a function (ignored otherwise). In particular, m is obtained from X when it is a BEDMatrix or a regular R matrix.
ind_keep	An optional vector of individuals to keep (as booleans or indexes, used to subset an R matrix).
loci_on_cols	Determines the orientation of the genotype matrix (by default, FALSE, loci are along the rows). If X is a BEDMatrix object, the input value is ignored (set automatically to TRUE internally).
mem_factor	Proportion of available memory to use loading and processing genotypes. Ignored if mem_lim is not NA.
mem_lim	Memory limit in GB, used to break up genotype data into chunks for very large datasets. Note memory usage is somewhat underestimated and is not controlled strictly. Default in Linux and Windows is mem_factor times the free system memory, otherwise it is 1GB (OSX and other systems).
m_chunk_max	Sets the maximum number of loci to process at the time. Actual number of loci loaded may be lower if memory is limiting.

Value

A list with the following named elements, in this order:

• fst: The genome-wide Fst estimate (scalar).

• fst_loci: A vector of per-locus Fst estimates.

• data: a 2-by-m matrix of statistics used in estimating Fst. Useful to obtain a bootstrap distribution for the genome-wide Fst.

• maf: a vector of marginal allele frequency estimates, one for each locus. Note that it has not been converted to minor allele frequencies.

See Also

The popkin package.

Examples

# dimensions of simulated data
n_ind <- 100
m_loci <- 1000
k_subpops <- 10
n_data <- n_ind * m_loci

# missingness rate
miss <- 0.1

# simulate ancestral allele frequencies
# uniform (0,1)
# it'll be ok if some of these are zero
p_anc <- runif(m_loci)

# simulate some binomial data
X <- rbinom(n_data, 2, p_anc)

# sprinkle random missingness
X[ sample(X, n_data * miss) ] <- NA

# turn into a matrix
X <- matrix(X, nrow = m_loci, ncol = n_ind)

# create subpopulation labels
# k_subpops groups of equal size
labs <- ceiling( (1 : n_ind) / k_subpops )

# estimate FST using the Weir-Hill formula
fst_wc_obj <- fst_wh(X, labs)

# the genome-wide FST estimate
fst_wc_obj$fst

# vector of per-locus FST estimates
fst_wc_obj$fst_loci

OchoaLab/popkinsuppl documentation built on May 17, 2022, 9:50 a.m.