[R] Adding Text to a Plot

[Peter Ehlers]

On 2012-05-22 07:51, David Winsemius wrote:
>
> On May 22, 2012, at 9:10 AM, Canto Casasola, Vicente David wrote:
>>
>> I'm pretty sure I'm missing something about this.
>>
>> Is there a smart way of typping hat(R)^2 and it's value from a linear
>> regression?
>>
>> I've just found this tricky one:
>>
>> # Sample data
>> x<- sample(1:100,10)
>> y<- 2+3*x+rnorm(10)
>>
>> # Run the regression
>> lm1<- lm(y~x)
>> # Plotting
>> plot(x,y, main="Linear Regression", col="red")
>> abline(lm1, col="blue")
>> placex<- par("usr")[1]+.1*(par("usr")[2]-par("usr")[1])
>> placey1<- par("usr")[3]+.9*(par("usr")[4]-par("usr")[3])
>> placey2<- par("usr")[3]+.8*(par("usr")[4]-par("usr")[3])
>>
>> # HERE: Is this the right way?
>
> # To do  .... what? I see that you over-plotted the R, presumably
> because you did not like the way that:
>     bquote(hat(R)^2 == .(summary(lm1)$adj.r.squared))
>
> ... ended up looking (with the exponent higher than in the non-hatted
> version.)
>
>>
>> text(x=placex, y=placey1,
>>      bquote(R^2 == .(summary(lm1)$r.squared)), adj=c(0,0))
>> text(x=placex, y=placey2,
>>      bquote(R^2 == .(summary(lm1)$adj.r.squared)), adj=c(0,0))
>> text(x=placex,y=placey2,
>>      expression(hat(R)), adj=c(0,0))
>>
>> In addition, when I save the plot as PDF, the expression hat(R)
>> seems to be
>> somewhat displaced.
>>
>> Any advice?
>>
> Are you sure? It "looks"  to me that the lower "R" is slightly shifted
> to the left, but when I actually measure it, there does not appear to
> be a shift. If it is real and not just an optical illusion, this may
> have something to do with your unstated version of R or your also
> unstated OS.

I don't see any shift either (Windows), easily checked with insert of an 
appropriate vertical line, but I would recommend not
overwriting the 'R' by using the phantom() construct:

   text(x=placex, y=placey2,
     bquote(phantom(R)^2 == .(summary(lm1)$adj.r.squared)), adj=c(0,0))
   text(x=placex, y=placey2,
     expression(hat(R)), adj=c(0,0))


Peter Ehlers

>
> --
> David Winsemius, MD
> West Hartford, CT