R help - Mar 2004 - Center labels on a boxplot

Suppose that I have data on three species for a variable and datasets
from two time periods. I want to make a boxplot of the first dataset and
then add the second using 'at = ' and 'add = T' as in the
example for
'boxplot.'

Since the boxes are paired by species, I want to do is have the x labels
be centered between the boxes. I'm doing this now with mtext and
entering spaces to make them center. There must be a better way.

Much thanks, Andy

   #######################
   myDF1 <- data.frame(spp1 = c(0,0,0,0,1,0,1,1,0,0,0,1), 
                        spp2 = c(1,0,1,1,0,0,0,0,1,0,0,0),
                        spp3 = c(0,1,0,0,0,1,0,0,0,1,1,0),
                        aVar = runif(12, 1, 10) + 1:12)

    myDF2 <- data.frame(spp1 = c(1,1,0,0,0,0,0,0,1,0,0,1), 
                        spp2 = c(0,0,1,1,0,0,0,1,0,0,1,0),
                        spp3 = c(0,0,0,0,1,1,1,0,0,1,0,0),
                        aVar = runif(12, 1, 10) + 1:12)

    boxplot(aVar ~ spp1 + spp2 + spp3, data = myDF1, boxwex = 0.25, at 1:3 -
0.2,
                       names = c("","",""), 
                       ylab = "A Varirable of Extreme Interest",
                       ylim = c(0,24))

    boxplot(aVar ~ spp1 + spp2 + spp3, data = myDF2, boxwex = 0.25, at 1:3 +
0.2,
                       names = c("","",""), add =
T, col="gray")
 
    legend(0.5, 24, c("Time 1", "Time 2"),
           fill = c("white", "gray"))    
 
    
   mtext("SPP1, SPP2, SPP3",.....)
   #########################

How about something like this suitably fixed up:

 par(mfrow=c(1,3)
 for(i in 1:3)
   boxplot( data.frame( a=myDF1[myDF1[i]==1,4],
                        b=myDF2[myDF2[i]==1,4]),xlab=i,ylim=c(0,25) )

On Wed, 2004-03-10 at 10:34, Andy Bunn wrote:
> Suppose that I have data on three species for a variable and datasets
> from two time periods. I want to make a boxplot of the first dataset and
> then add the second using 'at = ' and 'add = T' as in the
example for
> 'boxplot.'
> 
> Since the boxes are paired by species, I want to do is have the x labels
> be centered between the boxes. I'm doing this now with mtext and
> entering spaces to make them center. There must be a better way.
> 
> Much thanks, Andy
> 
>    #######################
>    myDF1 <- data.frame(spp1 = c(0,0,0,0,1,0,1,1,0,0,0,1), 
>                         spp2 = c(1,0,1,1,0,0,0,0,1,0,0,0),
>                         spp3 = c(0,1,0,0,0,1,0,0,0,1,1,0),
>                         aVar = runif(12, 1, 10) + 1:12)
> 
>     myDF2 <- data.frame(spp1 = c(1,1,0,0,0,0,0,0,1,0,0,1), 
>                         spp2 = c(0,0,1,1,0,0,0,1,0,0,1,0),
>                         spp3 = c(0,0,0,0,1,1,1,0,0,1,0,0),
>                         aVar = runif(12, 1, 10) + 1:12)
> 
>     boxplot(aVar ~ spp1 + spp2 + spp3, data = myDF1, boxwex = 0.25, at >
1:3 - 0.2,
>                        names = c("","",""), 
>                        ylab = "A Varirable of Extreme Interest",
>                        ylim = c(0,24))
> 
>     boxplot(aVar ~ spp1 + spp2 + spp3, data = myDF2, boxwex = 0.25, at >
1:3 + 0.2,
>                        names = c("","",""),
add = T, col="gray")
>  
>     legend(0.5, 24, c("Time 1", "Time 2"),
>            fill = c("white", "gray"))    
>  
>     
>    mtext("SPP1, SPP2, SPP3",.....)
>    #########################

Andy,

Your boxplots are at (1:3 - 0.2) and (1:3 + 0.2). Thus, the centers of
the pairs are at 1:3.

You can use:

mtext(side = 1, text = c("SPP1", "SPP2", "SPP3"),
at = 1:3, line = 2)

To place the pair labels in the centers along the x axis.

HTH,

Marc Schwartz

Hello Andy,

does

mtext(c("SPP1", "SPP2", "SPP3"), side=1,
at=c(1,2,3))

complete your script?

Thomas P.