[R] Legend positioning in scaled survival plot

[Uwe Ligges]

Rachel Pearce wrote:

> I am sorry that this is another novice question. I am having trouble
> using "legend" with the survival curve plot from the survival package,
> and I wonder if it is because I have rescaled my plot. 
> 
> Here is the relevant segment of code:
> 
> 
>>plot(survfit(Surv(OS,Status)~shortishcr1),main='Overall Survival by
> 
> factor',
> + xlab='Years',ylab='% surviving',lty=c(1,2),xscale=365.25,yscale=100)
> 
>>legend(5,80,c('Factor=1','Factor=2'),lty=c(1,2)) 
> 
> 
> Here the variable OS is in days, but I want to plot it in years, so I
> scale it; likewise y is scaled to a percentage.
> I am trying to position the legend in the rescaled x and y values.
> Legend returns no error, but no legend appears on the plot.


Ask for the real coordinatre system using
   par("usr")
and place the legend somewhere appropriate within these user coordinates.

Uwe Ligges


> If I exclude the scaling altogether:
> 
> 
>>plot(survfit(Surv(OS,Status)~shortishcr1),main='Overall Survival by
> 
> factor',
> + xlab='Years',ylab='% surviving',lty=c(1,2),)
> 
>>legend(1825,.8,c('Factor=1','Factor=2'),lty=c(1,2))
> 
> 
> then the legend appears exactly as expected.
> 
> Using the unscaled version of the legend call with the scaled plot,
> however, again no legend appears but no error is returned.
> 
> I suspect I am making some elementary mistake, but I just can't see it.
> It is so elementary that I can't find a similar question in the
> archives. Can someone help?
> 
> Here is my version information:
>          _              
> platform i386-pc-mingw32
> arch     i386           
> os       mingw32        
> system   i386, mingw32  
> status                  
> major    2              
> minor    0.1            
> year     2004           
> month    11             
> day      15             
> language R 
> 
> 
> Rachel
> 
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