#' Permutation test for genome scan with a single-QTL model
#'
#' Permutation test for a enome scan with a single-QTL model by
#' Haley-Knott regression or a linear mixed model, with possible
#' allowance for covariates.
#'
#' @param genoprobs Genotype probabilities as calculated by
#' [calc_genoprob()].
#' @param pheno A numeric matrix of phenotypes, individuals x phenotypes.
#' @param kinship Optional kinship matrix, or a list of kinship matrices (one
#' per chromosome), in order to use the LOCO (leave one chromosome
#' out) method.
#' @param addcovar An optional numeric matrix of additive covariates.
#' @param Xcovar An optional numeric matrix with additional additive covariates used for
#' null hypothesis when scanning the X chromosome.
#' @param intcovar An optional numeric matrix of interactive covariates.
#' @param weights An optional numeric vector of positive weights for the
#' individuals. As with the other inputs, it must have `names`
#' for individual identifiers.
#' @param reml If `kinship` provided: if `reml=TRUE`, use
#' REML; otherwise maximum likelihood.
#' @param model Indicates whether to use a normal model (least
#' squares) or binary model (logistic regression) for the phenotype.
#' If `model="binary"`, the phenotypes must have values in \eqn{[0, 1]}.
#' @param n_perm Number of permutation replicates.
#' @param perm_Xsp If TRUE, do separate permutations for the autosomes
#' and the X chromosome.
#' @param perm_strata Vector of strata, for a stratified permutation
#' test. Should be named in the same way as the rows of
#' `pheno`. The unique values define the strata.
#' @param chr_lengths Lengths of the chromosomes; needed only if
#' `perm_Xsp=TRUE`. See [chr_lengths()].
#' @param cores Number of CPU cores to use, for parallel calculations.
#' (If `0`, use [parallel::detectCores()].)
#' Alternatively, this can be links to a set of cluster sockets, as
#' produced by [parallel::makeCluster()].
#' @param ... Additional control parameters; see Details.
#'
#' @return If `perm_Xsp=FALSE`, the result is matrix of
#' genome-wide maximum LOD scores, permutation replicates x
#' phenotypes. If `perm_Xsp=TRUE`, the result is a list of
#' two matrices, one for the autosomes and one for the X
#' chromosome. The object is given class `"scan1perm"`.
#'
#' @details
#' If `kinship` is not provided, so that analysis proceeds by
#' Haley-Knott regression, we permute the rows of the phenotype data;
#' the same permutations are also applied to the rows of the
#' covariates (`addcovar`, `Xcovar`, and `intcovar`)
#' are permuted.
#'
#' If `kinship` is provided, we instead permute the rows of the
#' genotype data and fit an LMM with the same residual heritability
#' (estimated under the null hypothesis of no QTL).
#'
#' If `Xcovar` is provided and `perm_strata=NULL`, we do a
#' stratified permutation test with the strata defined by the rows of
#' `Xcovar`. If a simple permutation test is desired, provide
#' `perm_strata` that is a vector containing a single repeated
#' value.
#'
#' The `...` argument can contain several additional control
#' parameters; suspended for simplicity (or confusion, depending on
#' your point of view). `tol` is used as a tolerance value for linear
#' regression by QR decomposition (in determining whether columns are
#' linearly dependent on others and should be omitted); default
#' `1e-12`. `maxit` is the maximum number of iterations for
#' converence of the iterative algorithm used when `model=binary`.
#' `bintol` is used as a tolerance for converence for the iterative
#' algorithm used when `model=binary`. `eta_max` is the maximum value
#' for the "linear predictor" in the case `model="binary"` (a bit of a
#' technicality to avoid fitted values exactly at 0 or 1).
#'
#' @references Churchill GA, Doerge RW (1994) Empirical threshold
#' values for quantitative trait mapping. Genetics 138:963--971.
#'
#' Manichaikul A, Palmer AA, Sen S, Broman KW (2007) Significance
#' thresholds for quantitative trait locus mapping under selective
#' genotyping. Genetics 177:1963--1966.
#'
#' Haley CS, Knott SA (1992) A simple regression method for mapping
#' quantitative trait loci in line crosses using flanking markers.
#' Heredity 69:315--324.
#'
#' Kang HM, Zaitlen NA, Wade CM, Kirby A, Heckerman D, Daly MJ, Eskin
#' E (2008) Efficient control of population structure in model
#' organism association mapping. Genetics 178:1709--1723.
#'
#' @examples
#' # read data
#' iron <- read_cross2(system.file("extdata", "iron.zip", package="qtl2"))
#' \dontshow{iron <- iron[,c(10,18,"X")]}
#'
#' # insert pseudomarkers into map
#' map <- insert_pseudomarkers(iron$gmap, step=1)
#'
#' # calculate genotype probabilities
#' probs <- calc_genoprob(iron, map, error_prob=0.002)
#'
#' # grab phenotypes and covariates; ensure that covariates have names attribute
#' pheno <- iron$pheno
#' covar <- match(iron$covar$sex, c("f", "m")) # make numeric
#' names(covar) <- rownames(iron$covar)
#' Xcovar <- get_x_covar(iron)
#'
#' # strata for permutations
#' perm_strata <- mat2strata(Xcovar)
#'
#' # permutations with genome scan (just 3 replicates, for illustration)
#' operm <- scan1perm(probs, pheno, addcovar=covar, Xcovar=Xcovar,
#' n_perm=3, perm_strata=perm_strata)
#' summary(operm)
#'
#' # leave-one-chromosome-out kinship matrices
#' kinship <- calc_kinship(probs, "loco")
#'
#' # permutations of genome scan with a linear mixed model
#' \donttest{
#' operm_lmm <- scan1perm(probs, pheno, kinship, covar, Xcovar, n_perm=3,
#' perm_Xsp=TRUE, perm_strata=perm_strata,
#' chr_lengths=chr_lengths(map))
#' summary(operm_lmm)
#' }
#'
#' @seealso [scan1()], [chr_lengths()], [mat2strata()]
#' @export
scan1perm <-
function(genoprobs, pheno, kinship=NULL, addcovar=NULL, Xcovar=NULL,
intcovar=NULL, weights=NULL, reml=TRUE, model=c("normal", "binary"),
n_perm=1, perm_Xsp=FALSE, perm_strata=NULL, chr_lengths=NULL,
cores=1, ...)
{
if(is.null(genoprobs)) stop("genoprobs is NULL")
if(is.null(pheno)) stop("pheno is NULL")
# grab tol from dot args
dotargs <- list(...)
tol <- grab_dots(dotargs, "tol", 1e-12)
if(!is_pos_number(tol)) stop("tol should be a single positive number")
# normal or binary model?
model <- match.arg(model)
if(!is_pos_number(n_perm)) stop("n_perm should be a single positive integer")
# check that the objects have rownames
check4names(pheno, addcovar, Xcovar, intcovar)
# if Xcovar provided, the default is to do a stratified permutation test
if(is.null(perm_strata) && !is.null(Xcovar))
perm_strata <- mat2strata(Xcovar)
if(perm_Xsp) { # autosome/X chr-specific permutations
if(is.null(chr_lengths))
stop("Need to provide chr_lengths when perm_Xsp=TRUE")
is_x_chr <- attr(genoprobs, "is_x_chr")
# collapse to A/X
chr_lengths <- collapse_chr_lengths_to_AX(chr_lengths, is_x_chr)
if(any(chr_lengths < 1e-12))
stop("Autosome or X chromosome of length 0; skip perm_Xsp")
n_permX <- ceiling(n_perm * chr_lengths[["A"]] / chr_lengths[["X"]])
A <- scan1perm(genoprobs=genoprobs[,!is_x_chr], pheno=pheno,
kinship=subset_kinship(kinship, chr=!is_x_chr),
addcovar=addcovar, Xcovar=NULL, intcovar=intcovar, weights=weights,
reml=reml, model=model, n_perm=n_perm, perm_Xsp=FALSE,
perm_strata=perm_strata, chr_lengths=NULL, cores=cores, ...)
X <- scan1perm(genoprobs=genoprobs[,is_x_chr], pheno=pheno,
kinship=subset_kinship(kinship, chr=is_x_chr),
addcovar=addcovar, Xcovar=Xcovar, intcovar=intcovar, weights=weights,
reml=reml, model=model, n_perm=n_permX, perm_Xsp=FALSE,
perm_strata=perm_strata, chr_lengths=NULL, cores=cores, ...)
result <- list(A=A, X=X)
attr(result, "chr_lengths") <- chr_lengths
class(result$A) <- class(result$X) <- "matrix"
class(result) <- c("scan1perm", "list")
return(result)
}
# force things to be matrices
if(!is.matrix(pheno)) {
pheno <- as.matrix(pheno)
if(!is.numeric(pheno)) stop("pheno is not numeric")
}
if(is.null(colnames(pheno))) # force column names
colnames(pheno) <- paste0("pheno", seq_len(ncol(pheno)))
if(!is.null(addcovar)) {
if(!is.matrix(addcovar)) addcovar <- as.matrix(addcovar)
if(!is.numeric(addcovar)) stop("addcovar is not numeric")
}
if(!is.null(Xcovar)) {
if(!is.matrix(Xcovar)) Xcovar <- as.matrix(Xcovar)
if(!is.numeric(Xcovar)) stop("Xcovar is not numeric")
}
if(!is.null(intcovar)) {
if(!is.matrix(intcovar)) intcovar <- as.matrix(intcovar)
if(!is.numeric(intcovar)) stop("intcovar is not numeric")
}
# for binary model
if(model=="binary") {
if(!is.null(kinship))
stop("Can't yet account for kinship with model = \"binary\"")
pheno <- check_binary_pheno(pheno)
}
else {
# square-root of weights (only if model="normal")
weights <- sqrt_weights(weights) # also check >0 (and if all 1's, turn to NULL)
}
# check that kinship matrices are square with same IDs
kinshipIDs <- check_kinship(kinship, length(genoprobs))
# multiply kinship matrix by 2; rest is using 2*kinship
# see Almasy & Blangero (1998) https://doi.org/10.1086/301844
kinship <- double_kinship(kinship)
# find individuals in common across all arguments
# and drop individuals with missing covariates or missing *all* phenotypes
ind2keep <- get_common_ids(genoprobs, addcovar, Xcovar, intcovar,
kinshipIDs, weights, perm_strata, complete.cases=TRUE)
ind2keep <- get_common_ids(ind2keep, pheno[rowSums(is.finite(pheno)) > 0,,drop=FALSE])
if(length(ind2keep)<=2) {
if(length(ind2keep)==0)
stop("No individuals in common.")
else
stop("Only ", length(ind2keep), " individuals in common: ",
paste(ind2keep, collapse=":"))
}
# make sure addcovar is full rank when we add an intercept
addcovar <- drop_depcols(addcovar, TRUE, tol)
# make sure columns in intcovar are also in addcovar
addcovar <- force_intcovar(addcovar, intcovar, tol)
# drop things from Xcovar that are already in addcovar
Xcovar <- drop_xcovar(addcovar, Xcovar, tol)
if(!is.null(kinship)) { # fit linear mixed model
return(scan1perm_pg(genoprobs=genoprobs, pheno=pheno, kinship=kinship,
addcovar=addcovar, Xcovar=Xcovar, intcovar=intcovar,
weights=weights,
reml=reml, n_perm=n_perm, perm_strata=perm_strata,
cores=cores, ind2keep=ind2keep, ...))
}
if(model=="normal" && is.null(addcovar) && is.null(Xcovar) &&
is.null(intcovar) && is.null(weights)
&& sum(!is.finite(pheno[ind2keep,]))==0) # no covariates, no weights, no missing phenotypes
result <- scan1perm_nocovar(genoprobs=genoprobs,
pheno=pheno,
n_perm=n_perm,
perm_strata=perm_strata,
cores=cores,
ind2keep=ind2keep,
...)
else
result <- scan1perm_covar(genoprobs=genoprobs,
pheno=pheno,
addcovar=addcovar,
Xcovar=Xcovar,
intcovar=intcovar,
weights=weights,
model=model,
n_perm=n_perm,
perm_strata=perm_strata,
cores=cores,
ind2keep=ind2keep,
...)
result
}
# simplest version: no covariates, no weights, no missing phenotypes
scan1perm_nocovar <-
function(genoprobs, pheno, n_perm=1, perm_strata=NULL,
cores=1, ind2keep, ...)
{
# deal with the dot args
dotargs <- list(...)
tol <- grab_dots(dotargs, "tol", 1e-12)
stopifnot(tol > 0)
quiet <- grab_dots(dotargs, "quiet", TRUE)
check_extra_dots(dotargs, c("tol", "intcovar_method", "quiet", "max_batch"))
# set up parallel analysis
cores <- setup_cluster(cores)
if(!quiet && n_cores(cores)>1) {
message(" - Using ", n_cores(cores), " cores")
quiet <- TRUE # make the rest quiet
}
# max batch size
max_batch <- grab_dots(dotargs, "max_batch",
min(1000, ceiling(n_perm*length(genoprobs)*ncol(pheno)/n_cores(cores))))
# generate permutations
perms <- gen_strat_perm(n_perm, ind2keep, perm_strata)
# batch permutations
phe_batches <- batch_vec( rep(seq_len(ncol(pheno)), n_perm), max_batch)
perm_batches <- batch_vec( rep(seq_len(n_perm), each=ncol(pheno)), max_batch)
# drop cols in genotype probs that are all 0 (just looking at the X chromosome)
genoprob_Xcol2drop <- genoprobs_col2drop(genoprobs)
is_x_chr <- attr(genoprobs, "is_x_chr")
if(is.null(is_x_chr)) is_x_chr <- rep(FALSE, length(genoprobs))
# batches for analysis, to allow parallel analysis
run_batches <- data.frame(chr=rep(seq_len(length(genoprobs)), length(phe_batches)),
phe_batch=rep(seq_along(phe_batches), each=length(genoprobs)))
run_indexes <- seq_len(length(genoprobs)*length(phe_batches))
# subset the phenotypes
pheno <- pheno[ind2keep,,drop=FALSE]
nind <- nrow(pheno)
nullrss <- apply(pheno, 2, function(ph) nullrss_clean(as.matrix(ph), NULL, NULL, add_intercept=TRUE, tol))
# the function that does the work
by_group_func <- function(i) {
# deal with batch information, including individuals to drop due to missing phenotypes
chr <- run_batches$chr[i]
chrnam <- names(genoprobs)[chr]
phebatch <- phe_batches[[run_batches$phe_batch[i]]]
permbatch <- perm_batches[[run_batches$phe_batch[i]]]
# subset the genotype probabilities: drop cols with all 0s, plus the first column
Xcol2drop <- genoprob_Xcol2drop[[chrnam]]
if(length(Xcol2drop) > 0) {
pr <- genoprobs[[chr]][ind2keep,-Xcol2drop,,drop=FALSE]
pr <- pr[,-1,,drop=FALSE]
}
else
pr <- genoprobs[[chr]][ind2keep,-1,,drop=FALSE]
ph <- pheno[,phebatch,drop=FALSE]
for(col in seq_len(ncol(ph))) # permute columns
ph[,col] <- ph[perms[,permbatch[col]] , col]
# scan1 function taking clean data (with no missing values)
rss <- scan1_clean(pr, ph, NULL, NULL, NULL, add_intercept=TRUE, tol, "lowmem")
# calculate LOD score
lod <- nind/2 * (log10(nullrss[phebatch]) - log10(rss))
# return column maxima
apply(lod, 1, max, na.rm=TRUE)
}
# calculations in parallel
list_result <- cluster_lapply(cores, run_indexes, by_group_func)
# check for problems (if clusters run out of memory, they'll return NULL)
result_is_null <- vapply(list_result, is.null, TRUE)
if(any(result_is_null))
stop("cluster problem: returned ", sum(result_is_null), " NULLs.")
# reorganize results
result <- array(dim=c(length(genoprobs), n_perm, ncol(pheno)))
for(i in run_indexes) {
chr <- run_batches$chr[i]
phebatch <- phe_batches[[run_batches$phe_batch[i]]]
permbatch <- perm_batches[[run_batches$phe_batch[i]]]
for(j in seq_along(phebatch))
result[chr,permbatch[j], phebatch[j]] <- list_result[[i]][j]
}
result <- apply(result, c(2,3), max)
colnames(result) <- colnames(pheno)
class(result) <- c("scan1perm", "matrix")
result
}
# permutations with covariates and/or different batches of phenotypes
# also covers the case of a binary phenotype
scan1perm_covar <-
function(genoprobs, pheno, addcovar=NULL, Xcovar=NULL, intcovar=NULL,
weights=NULL, model=c("normal", "binary"),
n_perm=1, perm_strata=NULL, cores=1, ind2keep, ...)
{
model <- match.arg(model)
# deal with the dot args
dotargs <- list(...)
tol <- grab_dots(dotargs, "tol", 1e-12)
if(!is_pos_number(tol)) stop("tol should be a single positive number")
intcovar_method <- grab_dots(dotargs, "intcovar_method", "lowmem",
c("highmem", "lowmem"))
quiet <- grab_dots(dotargs, "quiet", TRUE)
if(model=="binary") {
bintol <- grab_dots(dotargs, "bintol", sqrt(tol))
if(!is_pos_number(bintol)) stop("bintol should be a single positive number")
eta_max <- grab_dots(dotargs, "eta_max", log(1-tol)-log(tol)) # for model="binary"
if(!is_pos_number(eta_max)) stop("eta_max should be a single positive number")
maxit <- grab_dots(dotargs, "maxit", 100)
if(!is_nonneg_number(maxit)) stop("maxit should be a single non-negative integer")
check_extra_dots(dotargs, c("tol", "intcovar_method", "quiet", "max_batch",
"maxit", "bintol", "eta_max"))
}
else {
check_extra_dots(dotargs, c("tol", "intcovar_method", "quiet", "max_batch"))
}
# set up parallel analysis
cores <- setup_cluster(cores)
if(!quiet && n_cores(cores)>1) {
message(" - Using ", n_cores(cores), " cores")
quiet <- TRUE # make the rest quiet
}
# max batch size
max_batch <- grab_dots(dotargs, "max_batch",
min(1000, ceiling(n_perm*length(genoprobs)*ncol(pheno)/n_cores(cores))))
# generate permutations
perms <- gen_strat_perm(n_perm, ind2keep, perm_strata)
# batch permutations
phe_batches <- batch_cols(pheno[ind2keep,,drop=FALSE], max_batch)
# drop cols in genotype probs that are all 0 (just looking at the X chromosome)
genoprob_Xcol2drop <- genoprobs_col2drop(genoprobs)
is_x_chr <- attr(genoprobs, "is_x_chr")
if(is.null(is_x_chr)) is_x_chr <- rep(FALSE, length(genoprobs))
# batches for analysis, to allow parallel analysis
run_batches <- data.frame(chr=rep(seq_len(length(genoprobs)), length(phe_batches)*n_perm),
phe_batch=rep(seq_along(phe_batches), each=length(genoprobs)*n_perm),
perm_batch=rep(rep(seq_len(n_perm), each=length(genoprobs), length(phe_batches))))
run_indexes <- seq_len(length(genoprobs)*length(phe_batches)*n_perm)
# the function that does the work
by_group_func <- function(i) {
# deal with batch information, including individuals to drop due to missing phenotypes
chr <- run_batches$chr[i]
chrnam <- names(genoprobs)[chr]
phebatch <- phe_batches[[run_batches$phe_batch[i]]]
permbatch <- run_batches$perm_batch[i]
phecol <- phebatch$cols
omit <- phebatch$omit
these2keep <- ind2keep # individuals 2 keep for this batch
if(length(omit) > 0) these2keep <- ind2keep[-omit]
if(length(these2keep)<=2) return(NULL) # not enough individuals
# apply permutation to the probs
# (I initially thought we'd need to apply these just to the rownames, but
# actually we've already aligned probs and pheno and so forth
# via ind2keep/these2keep, so now we need to just permute the rows)
#
# (also need some contortions here to keep the sizes the same)
pr <- genoprobs[[chr]][ind2keep,,,drop=FALSE]
pr <- pr[perms[,permbatch],,,drop=FALSE]
rownames(pr) <- ind2keep
pr <- pr[these2keep,,,drop=FALSE]
# subset the genotype probabilities: drop cols with all 0s, plus the first column
Xcol2drop <- genoprob_Xcol2drop[[chrnam]]
if(length(Xcol2drop) > 0) {
pr <- pr[,-Xcol2drop,,drop=FALSE]
}
pr <- pr[,-1,,drop=FALSE]
# subset the rest
ac <- addcovar; if(!is.null(ac)) ac <- ac[these2keep,,drop=FALSE]
Xc <- Xcovar; if(!is.null(Xc)) Xc <- Xc[these2keep,,drop=FALSE]
ic <- intcovar; if(!is.null(ic)) ic <- ic[these2keep,,drop=FALSE]
wts <- weights; if(!is.null(wts)) wts <- wts[these2keep]
ph <- pheno[these2keep, phecol, drop=FALSE]
# if X chr, paste X covariates onto additive covariates
# (only for the null)
if(is_x_chr[chr]) ac0 <- drop_depcols(cbind(ac, Xc), add_intercept=FALSE, tol)
else ac0 <- ac
if(model=="normal") {
# FIX_ME: calculating null RSS multiple times :(
nullrss <- nullrss_clean(ph, ac0, wts, add_intercept=TRUE, tol)
# scan1 function taking clean data (with no missing values)
rss <- scan1_clean(pr, ph, ac, ic, wts, add_intercept=TRUE, tol, intcovar_method)
# calculate LOD score
lod <- nrow(ph)/2 * (log10(nullrss) - log10(rss))
}
else { # binary model
# FIX_ME: calculating null LOD multiple times :(
nulllod <- null_binary_clean(ph, ac0, wts, add_intercept=TRUE, maxit, bintol, tol, eta_max)
# scan1 function taking clean data (with no missing values)
lod <- scan1_binary_clean(pr, ph, ac, ic, wts, add_intercept=TRUE,
maxit, bintol, tol, intcovar_method, eta_max)
# calculate LOD score
lod <- lod - nulllod
}
# return column maxima
apply(lod, 1, max, na.rm=TRUE)
}
# calculations in parallel
list_result <- cluster_lapply(cores, run_indexes, by_group_func)
# check for problems (if clusters run out of memory, they'll return NULL)
result_is_null <- vapply(list_result, is.null, TRUE)
if(any(result_is_null))
stop("cluster problem: returned ", sum(result_is_null), " NULLs.")
# reorganize results
result <- array(dim=c(length(genoprobs), n_perm, ncol(pheno)))
for(i in run_indexes) {
chr <- run_batches$chr[i]
phebatch <- phe_batches[[run_batches$phe_batch[i]]]
permbatch <- run_batches$perm_batch[i]
result[chr, permbatch, phebatch$cols] <- list_result[[i]]
}
result <- apply(result, c(2,3), max)
colnames(result) <- colnames(pheno)
class(result) <- c("scan1perm", "matrix")
result
}
# generate (potentially) stratified permutations
# (actual work is done in c++, see src/random.cpp)
gen_strat_perm <-
function(n_perm, ind2keep, perm_strata=NULL)
{
if(!is.null(perm_strata)) {
perm_strata <- perm_strata[ind2keep]
u <- unique(perm_strata)
if(length(u) > 1) {
strat_numeric <- match(perm_strata, u)-1
return(permute_nvector_stratified(n_perm,
seq_along(ind2keep),
strat_numeric,
length(u)))
}
}
permute_nvector(n_perm, seq_along(ind2keep))
}
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