histb2b <- function(x1,x2, direction=1, 
	names=NULL, breaks=NULL, 
	xlab="",ylab="",
	col=NULL, border="#444444", clinecol="#444444",
	xlim=NULL, ylim=NULL,
	...) {
### Comments:
#     x1 and x2: vectors of values to plot
#     direction: 1  x1 on top
#                2  x1 on left
#                3  x1 on bottom
#                4  x1 on right
#     names: lables for the two variables
#     breaks: usual breakpoints for the histograms
#             may be the number of breaks, or the breaks themselves
#     col: two colors for the histograms
#     border: the border collor for the histogram rectangles
#     clinecol: color for the center line
#
#
#     version: 0.2015.0624
#


# Check for defaults
if( length(col)<1 )   col=c(2,4)
if( length(col)>2 )   col=col[c(1,2)]

if( length(names)<1 ) names=c("","")
if( length(names)>2 ) names=names[c(1,2)]


if(length(breaks)==0) {
  breaks=seq( min(x1,x2), max(x1,x2), length=31 )
}

if(length(breaks)==1) {
  breaks=seq( min(x1,x2), max(x1,x2), length=breaks )
} 

# Alter items based on direction specified.
if(direction==3 || direction==4) {
  yy=x1; x1=x2; x2=yy
  yy=names[1]; names[1]=names[2]; names[2]=yy
}


# Create the two histograms
h1 = hist(x1, breaks=breaks, plot=FALSE)
h2 = hist(x2, breaks=breaks, plot=FALSE)


widest=max( c(h1$counts,h2$counts)*1.1 )


if(direction==1 || direction==3) {

  if( length(xlim)!=2 ) xlim=c( min(breaks),max(breaks) )

  # Start plot
  plot.new()
  plot.window( xlim=xlim, ylim=c(-widest,widest) )

  # Plot the histogram boxes
  for(i in 1:(length(breaks)-1)) {
    rect( h1$breaks[i],0, h1$breaks[i+1],-h1$counts[i], col=col[1], border=border)
    rect( h2$breaks[i],0, h2$breaks[i+1], h2$counts[i], col=col[2], border=border)
  }

  #Print the names
  text( min(breaks), -widest, names[1], pos=4 )
  text( min(breaks),  widest, names[2], pos=4 )
  abline(h=0, col=clinecol)

} else {  ### direction = 2 or 4

  if( length(ylim)!=2 ) ylim=c( min(breaks),max(breaks))
  
  # Start plot
  plot.new()
  plot.window( xlim=c(-widest,widest), ylim=ylim )

  # Plot the histogram boxes
  for(i in 1:(length(breaks)-1)) {
    rect( 0,h1$breaks[i], -h1$counts[i],h1$breaks[i+1], col=col[1], border=border)
    rect( 0,h2$breaks[i],  h2$counts[i],h2$breaks[i+1], col=col[2], border=border)
  }

  # Print the names
  text( -widest, min(breaks), names[1], pos=4 )
  text(  widest, min(breaks), names[2], pos=2 )
  abline(v=0, col=clinecol)

}



# END function
}