[R] lattice barchart with "negative" bars

[Luis Torgo]

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")
        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, 
                      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")


-- 
Luis Torgo
    FEP/LIACC, University of Porto   Phone : (+351) 22 607 88 30
    Machine Learning Group           Fax   : (+351) 22 600 36 54
    R. Campo Alegre, 823             email : ltorgo at liacc.up.pt
    4150 PORTO   -  PORTUGAL         WWW   : http://www.liacc.up.pt/~ltorgo