R/read_data.R

In MRCIEU/TwoSampleMR: Two Sample MR Functions and Interface to MR Base Database

#' Read outcome data
#'
#' Reads in outcome data. Checks and organises columns for use with MR or enrichment tests.
#' Infers p-values when possible from beta and se.
#'
#' @param filename Filename. Must have header with at least SNP column present.
#' @param snps SNPs to extract. If `NULL`, which the default, then doesn't extract any and keeps all.
#' @param sep Specify delimeter in file. The default is space, i.e. `sep=" "`.
#' @param phenotype_col Optional column name for the column with phenotype name corresponding the the SNP. If not present then will be created with the value `"Outcome"`. Default is `"Phenotype"`.
#' @param snp_col Required name of column with SNP rs IDs. The default is `"SNP"`.
#' @param beta_col Required for MR. Name of column with effect sizes. THe default is `"beta"`.
#' @param se_col Required for MR. Name of column with standard errors. The default is `"se"`.
#' @param eaf_col Required for MR. Name of column with effect allele frequency. The default is `"eaf"`.
#' @param effect_allele_col Required for MR. Name of column with effect allele. Must be "A", "C", "T" or "G". The default is `"effect_allele"`.
#' @param other_allele_col Required for MR. Name of column with non effect allele. Must be "A", "C", "T" or "G". The default is `"other_allele"`.
#' @param pval_col Required for enrichment tests. Name of column with p-value. The default is `"pval"`.
#' @param units_col Optional column name for units. The default is `"units"`.
#' @param ncase_col Optional column name for number of cases. The default is `"ncase"`.
#' @param ncontrol_col Optional column name for number of controls. The default is `"ncontrol"`.
#' @param samplesize_col Optional column name for sample size. The default is `"samplesize"`.
#' @param gene_col Optional column name for gene name. The default is `"gene"`.
#' @param id_col Optional column name to give the dataset an ID. Will be generated automatically if not provided for every trait / unit combination. The default is `"id"`.
#' @param min_pval Minimum allowed p-value. The default is `1e-200`.
#' @param log_pval The pval is -log10(P). The default is `FALSE`.
#' @param chr_col Optional column name for chromosome. Default is `"chr"`.
#' @param pos_col Optional column name for genetic position Default is `"pos"`.
#'
#' @export
#' @return data frame
read_outcome_data <- function(filename, snps=NULL, sep=" ", phenotype_col="Phenotype", snp_col="SNP", beta_col="beta", se_col="se", eaf_col="eaf", effect_allele_col="effect_allele", other_allele_col="other_allele", pval_col="pval", units_col="units", ncase_col="ncase", ncontrol_col="ncontrol", samplesize_col="samplesize", gene_col="gene", id_col="id", min_pval=1e-200, log_pval=FALSE, chr_col="chr", pos_col="pos")
{
	outcome_dat <- data.table::fread(filename, header=TRUE, sep=sep)
	outcome_dat <- format_data(
		as.data.frame(outcome_dat),
		type="outcome",
		snps=snps,
		phenotype_col=phenotype_col,
		snp_col=snp_col,
		beta_col=beta_col,
		se_col=se_col,
		eaf_col=eaf_col,
		effect_allele_col=effect_allele_col,
		other_allele_col=other_allele_col,
		pval_col=pval_col,
		units_col=units_col,
		ncase_col=ncase_col,
		ncontrol_col=ncontrol_col,
		samplesize_col=samplesize_col,
		gene_col=gene_col,
		id_col=id_col,
		min_pval=min_pval,
		log_pval=log_pval,
		chr_col=chr_col,
		pos_col=pos_col
	)
	outcome_dat$data_source.outcome <- "textfile"
	return(outcome_dat)
}

#' Read exposure data
#'
#' Reads in exposure data. Checks and organises columns for use with MR or enrichment tests.
#' Infers p-values when possible from beta and se.
#'
#' @param filename Filename. Must have header with at least SNP column present.
#' @param clump Whether to perform LD clumping with [clump_data()] on the exposure data. The default is `FALSE`.
#' @param sep Specify delimeter in file. The default is a space, i.e. `" "`.
#' @param phenotype_col Optional column name for the column with phenotype name corresponding the the SNP. If not present then will be created with the value "Outcome". The default is `"Phenotype"`.
#' @param snp_col Required name of column with SNP rs IDs. The default is `"SNP"`.
#' @param beta_col Required for MR. Name of column with effect sizes. The default is `"beta"`.
#' @param se_col Required for MR. Name of column with standard errors. The default is `"se"`.
#' @param eaf_col Required for MR. Name of column with effect allele frequency. The default is `"eaf"`.
#' @param effect_allele_col Required for MR. Name of column with effect allele. Must be "A", "C", "T" or "G". The default is `"effect_allele"`.
#' @param other_allele_col Required for MR. Name of column with non effect allele. Must be "A", "C", "T" or "G". The default is `"other_allele"`.
#' @param pval_col Required for enrichment tests. Name of column with p-value. The default is `"pval"`.
#' @param units_col Optional column name for units. The default is `"units"`.
#' @param ncase_col Optional column name for number of cases. The default is `"ncase"`.
#' @param ncontrol_col Optional column name for number of controls. The default is `"ncontrol"`.
#' @param samplesize_col Optional column name for sample size. The default is `"samplesize"`.
#' @param gene_col Optional column name for gene name. The default is `"gene"`.
#' @param id_col Optional column name to give the dataset an ID. Will be generated automatically if not provided for every trait / unit combination. The default is `"id"`.
#' @param min_pval Minimum allowed p-value. The default is `1e-200`.
#' @param log_pval The p-value is -log10(P). The default is `FALSE`.
#' @param chr_col Optional column name for chromosome. Default is `"chr"`.
#' @param pos_col Optional column name for genetic position Default is `"pos"`.
#'
#' @export
#' @return data frame
read_exposure_data <- function(filename, clump=FALSE, sep=" ", phenotype_col="Phenotype", snp_col="SNP", beta_col="beta", se_col="se", eaf_col="eaf", effect_allele_col="effect_allele", other_allele_col="other_allele", pval_col="pval", units_col="units", ncase_col="ncase", ncontrol_col="ncontrol", samplesize_col="samplesize", gene_col="gene", id_col="id", min_pval=1e-200, log_pval=FALSE, chr_col="chr", pos_col="pos")
{
	exposure_dat <- data.table::fread(filename, header=TRUE, sep=sep)
	exposure_dat <- format_data(
		as.data.frame(exposure_dat),
		type="exposure",
		snps=NULL,
		phenotype_col=phenotype_col,
		snp_col=snp_col,
		beta_col=beta_col,
		se_col=se_col,
		eaf_col=eaf_col,
		effect_allele_col=effect_allele_col,
		other_allele_col=other_allele_col,
		pval_col=pval_col,
		units_col=units_col,
		ncase_col=ncase_col,
		ncontrol_col=ncontrol_col,
		samplesize_col=samplesize_col,
		gene_col=gene_col,
		id_col=id_col,
		min_pval=min_pval,
		log_pval=log_pval,
		chr_col=chr_col,
		pos_col=pos_col
	)
	exposure_dat$data_source.exposure <- "textfile"
	if(clump)
	{
		exposure_dat <- clump_data(exposure_dat)
	}
	return(exposure_dat)
}

#' Read exposure or outcome data
#'
#' Reads in exposure data. Checks and organises columns for use with MR or enrichment tests. 
#' Infers p-values when possible from beta and se. 
#'
#' @param dat Data frame. Must have header with at least SNP column present.
#' @param type Is this the exposure or the outcome data that is being read in? The default is `"exposure"`.
#' @param snps SNPs to extract. If NULL then doesn't extract any and keeps all. The default is `NULL`.
#' @param header The default is `TRUE`.
#' @param phenotype_col Optional column name for the column with phenotype name corresponding the the SNP. If not present then will be created with the value `"Outcome"`. The default is `"Phenotype"`.
#' @param snp_col Required name of column with SNP rs IDs. The default is `"SNP"`.
#' @param beta_col Required for MR. Name of column with effect sizes. The default is `"beta"`.
#' @param se_col Required for MR. Name of column with standard errors. The default is `"se"`.
#' @param eaf_col Required for MR. Name of column with effect allele frequency. The default is `"eaf"`.
#' @param effect_allele_col Required for MR. Name of column with effect allele. Must contain only the characters "A", "C", "T" or "G". The default is `"effect_allele"`.
#' @param other_allele_col Required for MR. Name of column with non effect allele. Must contain only the characters "A", "C", "T" or "G". The default is `"other_allele"`.
#' @param pval_col Required for enrichment tests. Name of column with p-value. The default is `"pval"`.
#' @param units_col Optional column name for units. The default is `"units"`.
#' @param ncase_col Optional column name for number of cases. The default is `"ncase"`.
#' @param ncontrol_col Optional column name for number of controls. The default is `"ncontrol"`.
#' @param samplesize_col Optional column name for sample size. The default is `"samplesize"`.
#' @param gene_col Optional column name for gene name. The default is `"gene"`.
#' @param id_col The default is `"id"`.
#' @param min_pval Minimum allowed p-value. The default is `1e-200`.
#' @param z_col The default is `"z"`.
#' @param info_col The default is `"info_col"`.
#' @param chr_col The default is `"chr_col"`.
#' @param pos_col The default is `"pos"`.
#' @param log_pval The pval is -log10(P). The default is `FALSE`.
#'
#' @export
#' @return data frame
format_data <- function(dat, type="exposure", snps=NULL, header=TRUE, 
                        phenotype_col="Phenotype", snp_col="SNP", 
                        beta_col="beta", se_col="se", eaf_col="eaf", 
                        effect_allele_col="effect_allele", 
                        other_allele_col="other_allele", pval_col="pval", 
                        units_col="units", ncase_col="ncase", 
                        ncontrol_col="ncontrol", samplesize_col="samplesize", 
                        gene_col="gene", id_col="id", min_pval=1e-200, 
                        z_col="z", info_col="info", chr_col="chr", 
                        pos_col="pos", log_pval=FALSE)
{

if (inherits(dat, "data.table")) {
  datname <- deparse(substitute(dat))
  stop(paste0(
    "Your ", datname, " data.frame is also of class 'data.table', ",
    "please reformat as simply a data.frame with ", datname, " <- data.frame(",
    datname, ") and then rerun your format_data() call."
  ))
}

  all_cols <- c(phenotype_col, snp_col, beta_col, se_col, eaf_col, effect_allele_col, other_allele_col, pval_col, units_col, ncase_col, ncontrol_col, samplesize_col, gene_col, id_col, z_col, info_col, chr_col, pos_col)

	i <- names(dat) %in% all_cols
	if(sum(i) == 0)
	{
		stop("None of the specified columns present")
	}
	dat <- dat[,i]

	if(! snp_col %in% names(dat))
	{
		stop("SNP column not found")
	}

	names(dat)[names(dat) == snp_col] <- "SNP"
	snp_col <- "SNP"
	dat$SNP <- tolower(dat$SNP)
	dat$SNP <- gsub("[[:space:]]", "", dat$SNP)
	dat <- subset(dat, !is.na(SNP))

	if(!is.null(snps))
	{
		dat <- subset(dat, SNP %in% snps)
	}
	
	if(! phenotype_col %in% names(dat))
	{
		message("No phenotype name specified, defaulting to '", type, "'.")
		dat[[type]] <- type
	} else {
		dat[[type]] <- dat[[phenotype_col]]
		if(phenotype_col != type)
		{
			dat <- dat[,-which(names(dat)==phenotype_col)]
		}
	}

	if(log_pval)
	{
		dat$pval <- 10^-dat[[pval_col]]
	}

	# Remove duplicated SNPs
	dat <- plyr::ddply(dat, type, function(x){
		x <- plyr::mutate(x)
		dup <- duplicated(x$SNP)
		if(any(dup))
		{
			warning("Duplicated SNPs present in exposure data for phenotype '", x[[type]][1], ". Just keeping the first instance:\n", paste(x$SNP[dup], collapse="\n"))
			x <- x[!dup,]
		}
		return(x)		
	})

	# Check if columns required for MR are present
	mr_cols_required <- c(snp_col, beta_col, se_col, effect_allele_col) 
	mr_cols_desired <- c(other_allele_col, eaf_col)
	if(! all(mr_cols_required %in% names(dat)))
	{
		warning("The following columns are not present and are required for MR analysis\n", paste(mr_cols_required[!mr_cols_required %in% names(dat)]), collapse="\n")
		dat$mr_keep.outcome <- FALSE
	} else {
		dat$mr_keep.outcome <- TRUE
	}

	if(! all(mr_cols_desired %in% names(dat)))
	{
		warning("The following columns are not present but are helpful for harmonisation\n", paste(mr_cols_desired[!mr_cols_desired %in% names(dat)]), collapse="\n")
	}

	# Check beta
	i <- which(names(dat) == beta_col)[1]
	if(!is.na(i))
	{
		names(dat)[i] <- "beta.outcome"
		if(!is.numeric(dat$beta.outcome))
		{
			warning("beta column is not numeric. Coercing...")
			dat$beta.outcome <- as.numeric(dat$beta.outcome)
		}
		index <- !is.finite(dat$beta.outcome)
		index[is.na(index)] <- TRUE
		dat$beta.outcome[index] <- NA
	}

	# Check se
	i <- which(names(dat) == se_col)[1]
	if(!is.na(i))
	{
		names(dat)[i] <- "se.outcome"
		if(!is.numeric(dat$se.outcome))
		{
			warning("se column is not numeric. Coercing...")
			dat$se.outcome <- as.numeric(dat$se.outcome)
		}
		index <- !is.finite(dat$se.outcome) | dat$se.outcome <= 0
		index[is.na(index)] <- TRUE
		dat$se.outcome[index] <- NA
	}

	# Check eaf
	i <- which(names(dat) == eaf_col)[1]
	if(!is.na(i))
	{
		names(dat)[i] <- "eaf.outcome"
		if(!is.numeric(dat$eaf.outcome))
		{
			warning("eaf column is not numeric. Coercing...")
			dat$eaf.outcome <- as.numeric(dat$eaf.outcome)
		}
		index <- !is.finite(dat$eaf.outcome) | dat$eaf.outcome <= 0 | dat$eaf.outcome >= 1
		index[is.na(index)] <- TRUE
		dat$eaf.outcome[index] <- NA
	}

	# Check effect_allele
	i <- which(names(dat) == effect_allele_col)[1]
	if(!is.na(i))
	{
		names(dat)[i] <- "effect_allele.outcome"
		if(is.logical(dat$effect_allele.outcome))
		{
			dat$effect_allele.outcome <- substr(as.character(dat$effect_allele.outcome), 1, 1)
		}
		if(!is.character(dat$effect_allele.outcome))
		{
			warning("effect_allele column is not character data. Coercing...")
			dat$effect_allele.outcome <- as.character(dat$effect_allele.outcome)
		}

		dat$effect_allele.outcome <- toupper(dat$effect_allele.outcome)
		# index <- ! dat$effect_allele.outcome %in% c("A", "C", "T", "G")
		index <- ! (grepl("^[ACTG]+$", dat$effect_allele.outcome) | dat$effect_allele.outcome %in% c("D", "I"))
		index[is.na(index)] <- TRUE
		if(any(index))
		{
			warning("effect_allele column has some values that are not A/C/T/G or an indel comprising only these characters or D/I. These SNPs will be excluded.")
			dat$effect_allele.outcome[index] <- NA
			dat$mr_keep.outcome[index] <- FALSE
		}
	}


	# Check other_allele
	i <- which(names(dat) == other_allele_col)[1]
	if(!is.na(i))
	{
		names(dat)[i] <- "other_allele.outcome"
		if(is.logical(dat$other_allele.outcome))
		{
			dat$other_allele.outcome <- substr(as.character(dat$other_allele.outcome), 1, 1)
		}
		if(!is.character(dat$other_allele.outcome))
		{
			warning("other_allele column is not character data. Coercing...")
			dat$other_allele.outcome <- as.character(dat$other_allele.outcome)
		}

		dat$other_allele.outcome <- toupper(dat$other_allele.outcome)
		# index <- ! dat$other_allele.outcome %in% c("A", "C", "T", "G")
		index <- ! (grepl("^[ACTG]+$", dat$other_allele.outcome) | dat$other_allele.outcome %in% c("D", "I"))
		index[is.na(index)] <- TRUE
		if(any(index))
		{
			warning("other_allele column has some values that are not A/C/T/G or an indel comprising only these characters or D/I. These SNPs will be excluded")
			dat$other_allele.outcome[index] <- NA
			dat$mr_keep.outcome[index] <- FALSE
		}
	}


	# Check pval
	i <- which(names(dat) == pval_col)[1]
	if(!is.na(i))
	{
		names(dat)[i] <- "pval.outcome"
		if(!is.numeric(dat$pval.outcome))
		{
			warning("pval column is not numeric. Coercing...")
			dat$pval.outcome <- as.numeric(dat$pval.outcome)
		}
		index <- !is.finite(dat$pval.outcome) | dat$pval.outcome < 0 | dat$pval.outcome > 1
		index[is.na(index)] <- TRUE
		dat$pval.outcome[index] <- NA
		index <- dat$pval.outcome < min_pval
		index[is.na(index)] <- FALSE
		dat$pval.outcome[index] <- min_pval

		dat$pval_origin.outcome <- "reported"
		if(any(is.na(dat$pval.outcome)))
		{
			if("beta.outcome" %in% names(dat) & "se.outcome" %in% names(dat))
			{
				index <- is.na(dat$pval.outcome)
				dat$pval.outcome[index] <- stats::pnorm(abs(dat$beta.outcome[index])/dat$se.outcome[index], lower.tail=FALSE)
				dat$pval_origin.outcome[index] <- "inferred"
			}
		}
	}
	
	# If no pval column then create it from beta and se if available
	if("beta.outcome" %in% names(dat) & "se.outcome" %in% names(dat) & ! "pval.outcome" %in% names(dat))
	{
		message("Inferring p-values")
		dat$pval.outcome <- stats::pnorm(abs(dat$beta.outcome)/dat$se.outcome, lower.tail=FALSE) * 2
		dat$pval_origin.outcome <- "inferred"
	}
	

	if(ncase_col %in% names(dat))
	{
		names(dat)[which(names(dat) == ncase_col)[1]] <- "ncase.outcome"
		if(!is.numeric(dat$ncase.outcome))
		{
			warning(ncase_col, " column is not numeric")
			dat$ncase.outcome <- as.numeric(dat$ncase.outcome)
		}
	}
	if(ncontrol_col %in% names(dat))
	{
		names(dat)[which(names(dat) == ncontrol_col)[1]] <- "ncontrol.outcome"
		if(!is.numeric(dat$ncontrol.outcome))
		{
			warning(ncontrol_col, " column is not numeric")
			dat$ncontrol.outcome <- as.numeric(dat$ncontrol.outcome)
		}
	}

	

	if(samplesize_col %in% names(dat))
	{
		names(dat)[which(names(dat) == samplesize_col)[1]] <- "samplesize.outcome"
		if(!is.numeric(dat$samplesize.outcome))
		{
			warning(samplesize_col, " column is not numeric")
			dat$samplesize.outcome <- as.numeric(dat$samplesize.outcome)
		}

		if("ncontrol.outcome" %in% names(dat) & "ncase.outcome" %in% names(dat))
		{
			index <- is.na(dat$samplesize.outcome) & !is.na(dat$ncase.outcome) & !is.na(dat$ncontrol.outcome)
			if(any(index))
			{
				message("Generating sample size from ncase and ncontrol")
				dat$samplesize.outcome[index] <- dat$ncase.outcome[index] + dat$ncontrol.outcome[index]			
			}
		}
	} else if("ncontrol.outcome" %in% names(dat) & "ncase.outcome" %in% names(dat))
	{
		message("Generating sample size from ncase and ncontrol")
		dat$samplesize.outcome <- dat$ncase.outcome + dat$ncontrol.outcome
	}

	if(gene_col %in% names(dat))
	{
		names(dat)[which(names(dat) == gene_col)[1]] <- "gene.outcome"
	}
	
	if(info_col %in% names(dat))
	{
		names(dat)[which(names(dat) == info_col)[1]] <- "info.outcome"
	}

	if(z_col %in% names(dat))
	{
		names(dat)[which(names(dat) == z_col)[1]] <- "z.outcome"
	}

	if(chr_col %in% names(dat))
	{
		names(dat)[which(names(dat) == chr_col)[1]] <- "chr.outcome"
	}

	if(pos_col %in% names(dat))
	{
		names(dat)[which(names(dat) == pos_col)[1]] <- "pos.outcome"
	}

	if(units_col %in% names(dat))
	{
		names(dat)[which(names(dat) == units_col)[1]] <- "units.outcome"
		dat$units.outcome_dat <- as.character(dat$units.outcome)
		temp <- check_units(dat, type, "units.outcome")
		if(any(temp$ph))
		{
			dat[[type]] <- paste0(dat[[type]], " (", dat$units.outcome, ")")
		}
	}

	# Create id column
	if(id_col %in% names(dat))
	{
		names(dat)[which(names(dat) == id_col)[1]] <- "id.outcome"
		dat$id.outcome <- as.character(dat$id.outcome)
	} else {
		dat$id.outcome <- create_ids(dat[[type]])
	}

	if(any(dat$mr_keep.outcome))
	{
		mrcols <- c("SNP", "beta.outcome", "se.outcome", "effect_allele.outcome")
		mrcols_present <- mrcols[mrcols %in% names(dat)]
		dat$mr_keep.outcome <- dat$mr_keep.outcome & apply(dat[, mrcols_present], 1, function(x) !any(is.na(x)))
		if(any(!dat$mr_keep.outcome))
		{
			warning("The following SNP(s) are missing required information for the MR tests and will be excluded\n", paste(subset(dat, !mr_keep.outcome)$SNP, collapse="\n"))
		}
	}
	if(all(!dat$mr_keep.outcome))
	{
		warning("None of the provided SNPs can be used for MR analysis, they are missing required information.")
	}

	# Add in missing MR cols
	for(col in c("SNP", "beta.outcome", "se.outcome", "effect_allele.outcome", "other_allele.outcome", "eaf.outcome"))
	{
		if(! col %in% names(dat))
		{
			dat[[col]] <- NA
		}
	}

	names(dat) <- gsub("outcome", type, names(dat))
	rownames(dat) <- NULL
	return(dat)
}

check_units <- function(x, id, col)
{
	temp <- plyr::ddply(x, id, function(x1)
	{
		ph <- FALSE
		if(length(unique(x1[[col]])) > 1)
		{
			warning("More than one type of unit specified for ", x1[[id]][1])
			x1 <- plyr::mutate(x1)
			ph <- TRUE
		}
		return(data.frame(ph=ph[1], stringsAsFactors=FALSE))
	})
	return(temp)
}


#' Get data selected from GWAS catalog into correct format
#'
#' DEPRECATED. Please use [format_data()] instead.
#'
#' @param gwas_catalog_subset The GWAS catalog subset.
#' @param type The default is `"exposure"`.
#'
#' @export
#' @return Data frame
#' @examples \dontrun{
#' require(MRInstruments)
#' data(gwas_catalog)
#' bmi <- subset(gwas_catalog, Phenotype=="Body mass index" & Year==2010 & grepl("kg", Units))
#' bmi <- format_data(bmi)
#'}
format_gwas_catalog <- function(gwas_catalog_subset, type="exposure")
{
	message("This function is now deprecated and has been replaced by 'format_data'.")
	return(NULL)
}


#' Get data from eQTL catalog into correct format
#'
#' See [format_data()].
#'
#' @param gtex_eqtl_subset Selected rows from \code{gtex_eqtl} data loaded from \code{MRInstruments} package.
#' @param type Are these data used as `"exposure"` or `"outcome"`? Default is `"exposure"`.
#'
#' @export
#' @return Data frame
format_gtex_eqtl <- function(gtex_eqtl_subset, type="exposure")
{
	stopifnot(type %in% c("exposure", "outcome"))
	gtex_eqtl_subset[[type]] <- paste0(gtex_eqtl_subset$gene_name, " (", gtex_eqtl_subset$tissue, ")")

	if(length(unique(gtex_eqtl_subset[[type]])) > 1)
	{
		message("Separating the entries into the following phenotypes:\n", paste(unique(gtex_eqtl_subset[[type]]), collapse="\n"))
	}

	dat <- format_data(gtex_eqtl_subset, type=type, phenotype_col=type, pval_col="P_value", samplesize_col="n")
	dat[[paste0("data_source.", type)]] <- "gtex_eqtl"

	return(dat)

}


#' Get data from metabolomic QTL results
#'
#' See [format_data()].
#' 
#' @param metab_qtls_subset Selected rows from \code{metab_qtls} data loaded from \code{MRInstruments} package.
#' @param type Are these data used as `"exposure"` or `"outcome"`? Default is `"exposure"`.
#'
#' @export
#' @return Data frame
format_metab_qtls <- function(metab_qtls_subset, type="exposure")
{
	stopifnot(type %in% c("exposure", "outcome"))
	

	if(length(unique(metab_qtls_subset$phenotype)) > 1)
	{
		message("Separating the entries into the following phenotypes:\n", paste(unique(metab_qtls_subset$phenotype), collapse="\n"))
	}

	dat <- format_data(metab_qtls_subset, type=type, phenotype_col="phenotype")
	dat[[paste0("data_source.", type)]] <- "metab_qtls"

	return(dat)
}



#' Get data from proteomic QTL results
#'
#' See [format_data()].
#'
#' @param proteomic_qtls_subset Selected rows from \code{proteomic_qtls} data loaded from \code{MRInstruments} package.
#' @param type Are these data used as `"exposure"` or `"outcome"`? Default is `"exposure"`.
#'
#' @export
#' @return Data frame
format_proteomic_qtls <- function(proteomic_qtls_subset, type="exposure")
{
	stopifnot(type %in% c("exposure", "outcome"))
	

	if(length(unique(proteomic_qtls_subset$analyte)) > 1)
	{
		message("Separating the entries into the following phenotypes:\n", paste(unique(proteomic_qtls_subset$analyte), collapse="\n"))
	}

	dat <- format_data(proteomic_qtls_subset, type=type, phenotype_col="analyte")
	dat[[paste0("data_source.", type)]] <- "proteomic_qtls"

	return(dat)
}



#' Get data from methylation QTL results
#'
#' See [format_data()].
#'
#' @param aries_mqtl_subset Selected rows from \code{aries_mqtl} data loaded from \code{MRInstruments} package.
#' @param type Are these data used as `"exposure"` or `"outcome"`? Default is `"exposure"`.
#'
#' @export
#' @return Data frame
format_aries_mqtl <- function(aries_mqtl_subset, type="exposure")
{
	stopifnot(type %in% c("exposure", "outcome"))
	
	aries_mqtl_subset$Phenotype <- paste0(aries_mqtl_subset$cpg, " (", aries_mqtl_subset$age, ")")

	if(length(unique(aries_mqtl_subset$Phenotype)) > 1)
	{
		message("Separating the entries into the following phenotypes:\n", paste(unique(aries_mqtl_subset$Phenotype), collapse="\n"))
	}

	dat <- format_data(aries_mqtl_subset, type=type)
	dat[[paste0("data_source.", type)]] <- "aries_mqtl"

	return(dat)
}


random_string <- function(n=1, len=6)
{
	randomString <- c(1:n)
	for (i in 1:n)
	{
		randomString[i] <- paste(sample(c(0:9, letters, LETTERS),
		len, replace=TRUE),
		collapse="")
	}
	return(randomString)
}

create_ids <- function(x)
{
	a <- as.factor(x)
	levels(a) <- random_string(length(levels(a)))
	a <- as.character(a)
	return(a)
}


#' Combine data
#'
#' Taking exposure or outcome data (returned from [format_data()])
#' combine multiple datasets together so they can be analysed in one
#' batch. Removes duplicate SNPs, preferentially keeping those usable
#' in MR analysis.
#'
#' @param x List of data frames returned from [format_data()].
#'
#' @export
#' @return data frame
combine_data <- function(x)
{
	stopifnot(is.list(x))
	if("exposure" %in% names(x[[1]])) type <- "exposure"
	else if("outcome" %in% names(x[[1]])) type <- "outcome"
	else stop("Datasets must be generated from format_data")

	check <- all(sapply(x, function(i) {
		type %in% names(i)}))

	if(!check)
	{
		stop("Not all datasets or of type '", type, "'")
	}

	id_col <- paste0("id.", type)
	mr_keep_col <- paste0("mr_keep.", type)
	x <- plyr::rbind.fill(x)

	x <- plyr::ddply(x, id_col, function(x)
	{
		x <- plyr::mutate(x)
		x <- x[order(x[[mr_keep_col]], decreasing=TRUE), ]
		x <- subset(x, !duplicated(SNP))
		return(x)
	})

	rownames(x) <- NULL
	return(x)
}


#' Convert outcome data to exposure data
#'
#' Helper function to convert results from [extract_outcome_data()] to \code{exposure_dat} format.
#'
#' @param outcome_dat Output from [extract_outcome_data()].
#'
#' @export
#' @return data frame
convert_outcome_to_exposure <- function(outcome_dat)
{
	id <- subset(outcome_dat, !duplicated(outcome), select=c(outcome, id.outcome))
	exposure_dat <- format_data(
		outcome_dat,
		beta_col = "beta.outcome",
		se_col="se.outcome",
		pval_col="pval.outcome",
		phenotype_col="outcome",
		effect_allele_col="effect_allele.outcome",
		other_allele_col="other_allele.outcome",
		eaf_col="eaf.outcome",
		units_col="units.outcome"
	)
	exposure_dat <- merge(exposure_dat, id, by.x="exposure", by.y="outcome")
	exposure_dat <- subset(exposure_dat, select=-c(id.exposure))
	names(exposure_dat)[names(exposure_dat) == "id.outcome"] <- "id.exposure"
	return(exposure_dat)
}