R/merge_bed.R

In sgrote/ABAEnrichment: Gene expression enrichment in human brain regions

## take a bed-like-file and merge overlapping regions
## (for merging candidate into background regions in ABAEnrichment)


# merging for one chrom, input is sorted
merge_chrom = function(chrbed){ 
    # go through regions and merge with neighbor region
    i = 1
    while (i < nrow(chrbed)){   # last line cannot be changed
        # (a) no overlap    (stop before next start)
        if (chrbed[i,3] < chrbed[i+1,2]){
            i = i+1
        } 
        # (b) including the next region
        else if (chrbed[i,3] >= chrbed[i+1,3]){
            chrbed = chrbed[-(i+1),]
        }       
        # (c) included in next region (sorted by start,end -> must be included if starts are identical)
        else if (chrbed[i,2] == chrbed[i+1,2]){
            chrbed = chrbed[-i,]
        }       
        # (d) overlapping next region
        else if (chrbed[i,3] >= chrbed[i+1,2]){
            chrbed[i,3] = chrbed[i+1,3]
            chrbed = chrbed[-(i+1),]
        }
    }
    return(chrbed)
}

merge_bed = function(bed){
    # check that start < stop (athough this is already done in get_genes_from_regions...), for completeness
    if (any(bed[,2] > bed[,3])){
        stop("Genomic regions must be defined with start < stop.")
    }
    # sort
    bed = bed[order(bed[,1],bed[,2],bed[,3]),]
    # merge
    out = do.call(rbind,by(bed, bed[,1], merge_chrom))
    rownames(out) = 1:nrow(out)
    return(out)
}


#### for TESTING
### print before and after merging
#plot_bed = function(bed){
#   plot(1,type="n",ylim=range(chroms),xlim=range(c(starts,stops)),xlab="",ylab="")
#   apply(bed,1,function(reg) lines(c(reg[2],reg[3]),c(reg[1],reg[1])+runif(1,-0.1,0.1)))
#}
#chroms = c(1,1,1,2,2,2,2,2,2,3,3,4,4,4,5,5,5,5)
#starts = c(2,4,10,2,2,2,7,7,7,1,3,8,2,5,1,7,2,3)
#stops = c(3,10,12,5,5,5,9,8,10,4,5,10,7,6,2,9,4,5)
#bed = data.frame(chroms,starts,stops)
#par(mfrow=c(1,2))
#plot_bed(bed)
#bed_merged = merge_bed(bed)
#plot_bed(bed_merged)