Re: [R] "lwd" gives different plotted line widths for Vertical and horizontal Lines when lwd= 2?

From: Pedro de Barros <pbarros_at_ualg.pt>
Date: Sun, 06 Jul 2008 16:06:06 +0100

Hi Hadley,

Thanks for the quick and informative reply.

I did what you suggested, and it was indeed the problem for the axes lines (both are the same thickness). However, ticks are still thicker... I am attaching the two pdf files (one with lwd=2, the other with lwd=3).

Thanks again,
Pedro
At 15:02 2008/07/06, you wrote:
>On Sun, Jul 6, 2008 at 6:33 AM, Pedro de Barros <pbarros@ualg.pt> wrote:
> > Dear All,
> >
> > I have been trying to add lines to the axis grobs of plots produced with
> > ggplot2.
> >
> > The code I have used is below. It works, although I do not think it is a
> > really elegant way of doing what I want....
> > However, I am now noticing that when plotted, the width of the lines in the
> > axis are not the same as the line widths I get for the ticks (the ticks get
> > thicker lines). Also, when I build a function to do the same conversion, I
> > get different (thinner) line widths for the x-axis I have been trying to
> > find out why this is so, but I seem to have met a dead-end.
> >
> > #Test
> > library(ggplot2)
> > #Set the basic overall plot options
> > themePublish <-list(background.fill='white', grid.fill='white',
> > grid.colour='NA', grid.minor.colour='NA', axis.colour='black',
> > border.colour='NA')
> > ggtheme(themePublish)
> >
> > #Generate the data
> > plotdata<-data.frame(x=1:10, y=runif(10))
> >
> > #Build the ggplot object
> >
> > ggPlotObject<-ggplot()
> > ggPlotObject<-ggPlotObject+layer(data=plotdata,
> > mapping=aes_string(x='x',y='y'),geom='point', stat='identity', size=4)
> > ggPlotObject<-ggPlotObject+ scale_y_continuous(limits=c(0,1),
> expand=c(0,0))
> >
> > #################
> > #I define the following function
> > F.ggPlot.AddAxisLines<-function(ggPlotObject, col='black', lwd=2,
> > lty='solid'){
> >
> ###################################################################################################
> > # First, capture the ggPlot object as a gTree
> > ggPlotTree<-ggplot_plot(ggPlotObject)
> >
> > #Get the parameters defined for the lines
> > LinePars <- gpar(col=col, lwd=lwd, lty=lty)
> >
> > #Then, create the objects to add to the axes
> > YAxis.Line<-linesGrob(x=unit(c(1,1), 'npc'), y=unit(c(0,1), 'npc'),
> > vp='left_axis', name='YAxisLine', gp=LinePars)
> > XAxis.Line<-linesGrob(x=unit(c(0,1), 'npc'), y=unit(c(1,1), 'npc'),
> > vp='bottom_axis', name='XAxisLine', gp=LinePars)
> >
> > #Add the grobs to this object
> > ggPlotTreeMod<-ggPlotTree
> > ggPlotTreeMod<-addGrob(ggPlotTreeMod, YAxis.Line, gPath('yaxis'),
> grep=TRUE)
> > ggPlotTreeMod<-addGrob(ggPlotTreeMod, XAxis.Line, gPath('xaxis'),
> grep=TRUE)
> >
> > #Edit the properties of the ticks, to match those of the lines
> > ggPlotTreeMod<-editGrob(ggPlotTreeMod, gPath('ticks'), gp=LinePars,
> > grep=TRUE, global=TRUE)
> >
> > #Output the new object
> >
> > ggPlotTreeMod
> > }
> >
> > # and then do
> > ggPlotTreeMod2 <- F.ggPlot.AddAxisLines(ggPlotObject)
> > grid.draw(ggPlotTreeMod2)
> >
> > # I get different line thicknesses for the two axes
> >
> > #However, if I do
> > ggPlotTreeMod3 <- F.ggPlot.AddAxisLines(ggPlotObject, lwd=3)
> > grid.draw(ggPlotTreeMod3)
> >
> > # I get the same line thickness on both axes, but thicker ticks
>
>How are you judging thickness? It may be that due to the size of
>ticks and the size of the plot surface that thickness of the line is
>not a whole number of pixels, and depending on the exact position of
>the line, gets rounded up or down. Trying saving as pdf and zooming
>in.
>
>Hadley
>
>--
>http://had.co.nz/



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