[R] lattice barchart with "negative" bars

[Deepayan Sarkar]

On Tuesday 10 December 2002 12:15 pm, Luis Torgo wrote:
> On Tuesday 10 December 2002 14:30, Deepayan Sarkar wrote:
> > No, I don't think so (short of using a modified panel.barchart, which
> > should be relatively easy -- panel.barchart essentially has just 3 lines
> > of code). But this seems very reasonable thing to want, so I'll add an
> > option for this.
> >
> > You could also use xyplot with type = "h", but that will give you lines
> > instead of bars.
>
> Thank you for your help. You are right it is easy to adapt panel.barchart
> to perform what I wanted. As such, while you do not add an option for that,
> I've took the liberty to create my version of panel.barchart to solve the
> problem temporarily. I herein include it together with a simple example
> use, in case somebody has the same problem as me.
>
> The function works almost fine. The only problem I was not able to get
> around is the zero value reference line I want to draw in the case of
> horizontal bars. I've used the grid.lines function. It works fine for
> vertical bars, but it doesn't work for horizontal bars...
>
> Luis Torgo
>
>
> # Adapted from the code of panel.barchart by Deepayan Sarkar
> my.panel.barchart <- function (x, y, box.ratio = 1, horizontal = TRUE, col
> = bar.fill$col,
>     ...)
> {
>     x <- as.numeric(x)
>     y <- as.numeric(y)
>     bar.fill <- trellis.par.get("bar.fill")
>     if (horizontal) {
>         height <- box.ratio/(1 + box.ratio)
>         grid.lines(x=0,y=unit(c(0,1),"npc"),default.units="native")

This seems to need x = c(0,0). It's slightly odd that this works in the other 
case. In any case, 

          panel.abline(v = 0) ## correspondingly, h = 0 below

might be a more elegant solution.

>         for (i in seq(along = x))
>           if (x[i] >= 0)
>             grid.rect(gp = gpar(fill = col), y = y[i], x = 0,
>                       height = height, width = y[i] - 0,
                                         ^^^^^^^^^^^^^^^^
Typo here, should be                     width = x[i] - 0,

>                       just = c("left", "centre"), default.units = "native")
>           else
>             grid.rect(gp = gpar(fill = col), y = y[i], x = x[i],
>                       height = height, width = 0 - x[i],
>                       just = c("left", "centre"), default.units = "native")
>     }
>     else {
>         width <- box.ratio/(1 + box.ratio)
>         grid.lines(x=unit(c(0,1),"npc"),y=0,default.units="native")
>         for (i in seq(along = y))
>           if (y[i] >= 0)
>             grid.rect(gp = gpar(fill = col), x = x[i], y = 0,
>                       height = y[i] - 0, width = width,
>                       just = c("centre", "bottom"), default.units =
> "native") else
>             grid.rect(gp = gpar(fill = col), x = x[i], y = y[i],
>                       height = 0 - y[i], width = width,
>                       just = c("centre", "bottom"), default.units =
> "native") }
> }
>
> # Example using the function
>
> my.data <-
> data.frame(var=c(34,-10,25,-40),season=c('s','w','s','w'),site=c('A','A','B
>','B'))
>
> barchart(var ~ season | site, data=my.data, panel="my.panel.barchart")