[R] plotmath vector problem; full program enclosed

[Paul Johnson]

On Wed, Jul 7, 2010 at 5:41 AM, Duncan Murdoch <murdoch.duncan at gmail.com> wrote:

>>>>
>>>
>>> You want "as.expression(b1)", not "expression(b1)".  The latter means
>>> "the
>>> expression consisting of the symbol b1".  The former means "take the
>>> object
>>> stored in b1, and convert it to an expression.".
>>>

Thanks to Duncan and Allen, who pointed out that I was not even
reading my own code carefully.  I apologize for trying your patience.

Before I stop swinging at this one, I still want to bother everybody
about one thing, which really was the original question, but I did not
know the words to ask it.

The full code below is a working example that works, but I don't
understand why. Focus on these two commands that produce 2 axes.  Both
produce the desired output, but, as far as I can see, they should not!

1:
   axis(1, line=6, at=mu+dividers*sigma,
labels=as.expression(c(b1,b2,b3,b4,b5), padj=-1))


2:
   axis(1, line=9, at=mu+dividers*sigma,
labels=c(as.expression(b1),b2,b3,b4,b5), padj=-1)

This second one shouldn't work, I think.
It has as.expression on only the first element, and yet they all come
out right. Is there a spill over effect?

My original question should not have asked why b1 does not print
correctly when I do this:

   axis(1, line=9, at=mu+dividers*sigma,
labels=c(expression(b1),b2,b3,b4,b5), padj=-1)

but the correct question should have been "why do b2, b3, b4 , and b5"
get processed properly into plot math even though they are not
expressions??

???
pj

### Filename: plotMathProblem.R
### Paul Johnson July 7, 2010
### email me <pauljohn at ku.edu>

  sigma <- 10.0
  mu <- 4.0

  myx <- seq( mu - 3.5*sigma,  mu+ 3.5*sigma, length.out=500)

  myDensity <- dnorm(myx,mean=mu,sd=sigma)

  ### xpd needed to allow writing outside strict box of graph
  ### Need big bottom margin to add several x axes
  par(xpd=TRUE, ps=10, mar=c(18,2,2,2))

  plot(myx, myDensity, type="l", xlab="", ylab="Probability Density ",
main=myTitle1, axes=FALSE)
  axis(2, pos= mu - 3.6*sigma)
  axis(1, pos=0)

  lines(c(myx[1],myx[length(myx)]),c(0,0)) ### closes off axes


  addInteriorLine <- function(x, m, sd){
    for (i in 1:(length(x))){
      lines( c(x[i],x[i]), c(0, dnorm(x[i],m=m,sd=sd)), lty= 14, lwd=.2)
    }
  }


  dividers <- c(qnorm(0.025), -1, 0, 1, qnorm(0.975))
  addInteriorLine(mu+sigma*dividers, mu,sigma)

  # bquote creates an expression that text plotters can use
  t1 <-  bquote( mu== .(mu))
  mtext(bquote( mu == .(mu)), 1, at=mu, line=-1)


  addInteriorLabel <- function(pos1, pos2, m, s){
    area <- abs(100*( pnorm(m+pos1*s,m,s)-pnorm(m+pos2*s, m,s)))
    mid <- m+0.5*(pos1+pos2)*s
    text(mid, 0.5*dnorm(mid,m,s),label=paste(round(area,2),"%"))
  }


  addInteriorLabel(dividers[1],dividers[2],  mu, sigma)
  addInteriorLabel(dividers[2],dividers[3],  mu, sigma)
  addInteriorLabel(dividers[3],dividers[4],  mu, sigma)
  addInteriorLabel(dividers[4],dividers[5],  mu, sigma)

   b1 <- substitute( mu - d*sigma, list(d=round(dividers[1],2)) )
   b2 <- substitute( mu - sigma )
   b3 <- substitute( mu )
   b4 <- substitute( mu + sigma )
   b5 <- substitute( mu + d*sigma, list(d=round(dividers[5],2)) )
   axis(1, line=4, at=mu+dividers*sigma, labels=c(b1,b2,b3,b4,b5), padj=-1)


   axis(1, line=6, at=mu+dividers*sigma,
labels=as.expression(c(b1,b2,b3,b4,b5), padj=-1))



   axis(1, line=9, at=mu+dividers*sigma,
labels=c(as.expression(b1),b2,b3,b4,b5), padj=-1)


-- 
Paul E. Johnson
Professor, Political Science
1541 Lilac Lane, Room 504
University of Kansas