Re: [R] help on barplots

From: Marc Schwartz <MSchwartz_at_mn.rr.com>
Date: Tue 20 Dec 2005 - 01:05:21 EST

On Mon, 2005-12-19 at 12:27 +0100, Björn Rogell wrote:
> Hello, I am a beginner with R and I would need some help with doing
> barplots.
> My problem is that I would like to include both diffrent colors of the
> bars
> and precence/absence of shading lines in the barplots. When reading
> in the
> help file about the "col" command it states:
>
> col: a vector of colors for the bars or bar components. By
> default, grey is used if 'height' is a vector, and a
> gamma-corrected grey palette if 'height' is a matrix.
>
> It seems like the default is to color the bar components, when I add
> both
> col and density the shading lines gets the colors in the col vector.
> What I
> would need is diffrent colors of the bars and black shading lines.
> How could I solve this problem?
> Thanksful for answer/ Björn Rogell
>
>
> > meanbufoAN
> TR101 TR203 TR302 TR404 TR509 TR611
> TR710
> TR812
> 12.329885 12.712815 12.115556 12.570500 11.580300 11.920851 10.094532
> 9.854988
>
> barplotANbufo<-barplot(meanbufoAN,ylim=c(0,15),col=c("white","lightgrey","white",
>
> "lightgrey","white","lightgrey","white","lightgrey"),
>
> names.arg=c("1","2","2","4","5","6","7","8"),density=c(0,0,12,12,0,0,12,12),xlab="",
> ylab="Length")

The problem here is that the bars are drawn within barplot() using rect(), which does not allow for both bar colors and line shadings simultaneously. However, there is a workaround.

This involves drawing the initial barplot using the colors that you want for the bars and then using barplot a second time, with 'add = TRUE' and 'col = NA'. The former will 'overplot' the initial barplot without clearing the plot device first. The latter will draw the shading lines, but using a transparent background color, so that it retains the initial bar colors.

Thus:

barplotANbufo <- barplot(meanbufoAN, ylim = c(0, 15),

                         col = c("white", "lightgrey"),
                         names.arg = c(1, 2, 2, 4:8),
                         xlab="", ylab="Length")

barplot(meanbufoAN, ylim = c(0, 15), col = NA,
        density = rep(c(0, 12), 2, each = 2),
        axes = FALSE, add = TRUE)

Note also some efficiencies in the specification of the colors (which will be recycled), names.arg (presuming that the '2' should be there twice) and density in the second call using rep().

HTH, Marc Schwartz



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