R help - Dec 2002 - Problems with segments and multiple graphs

I would like to create a page of two graphs (2 rows by 1 col) and then
draw vertical lines (segments?) on both graphs from the minimum
values to the corresponding maximum value.

So I have tried

#
> y <- rnorm(3000)
> par(mfrow=c(2,1))
> plot(y,type="l")
> plot(cumsum(y),type="l")
> segments(1000,min(cumsum(y)),1000,max(cumsum(y)))
> par(mfg=c(1,1))
> segments(1000,min(y),1000,max(y))
> y <- rnorm(3000)

The segment looks fine on the bottom graph but I get a small vertical
line on the top graph. The max(y) value looks OK but the min(y) looks
like the second largest value.
> ymin <- min(y)
> ymax <- max(y)
> segments(1000,ymin,1000,ymax)
doesn't make any difference.

Can I draw a (one) line that crosses both graphs?

Thanks 

Ross Darnell
-- 
Ross Darnell
Email: <r.darnell at shrs.uq.edu.au>

Hi,

there are perhaps problems with par(mfg) and coordinate system (at
least on my R 1.5.1 on RH 7.2).  But you may do

  y <- rnorm(3000)
  par(mfrow=c(2,1))
  plot(y,type="l")
  segments(1000,min(y),1000,max(y), col=2)
  plot(cumsum(y),type="l")
  segments(1000,min(cumsum(y)),1000,max(cumsum(y)), col=3)

i.e. plot and draw segment on upper graph, and thereafter do the same
on the lower.  Plot starts a new graph, but segements works on the
previous one.

Perhaps it helps.

Ott

 | From: Ross Darnell <r.darnell at shrs.uq.edu.au>
 | Date: 05 Dec 2002 14:46:20 +1000
 | 
 | I would like to create a page of two graphs (2 rows by 1 col) and then
 | draw vertical lines (segments?) on both graphs from the minimum
 | values to the corresponding maximum value.
 | 
 | So I have tried
 | 
 | #
 | > y <- rnorm(3000)
 | > par(mfrow=c(2,1))
 | > plot(y,type="l")
 | > plot(cumsum(y),type="l")
 | > segments(1000,min(cumsum(y)),1000,max(cumsum(y)))
 | > par(mfg=c(1,1))
 | > segments(1000,min(y),1000,max(y))
 | > y <- rnorm(3000)
 | 
 | 
 | The segment looks fine on the bottom graph but I get a small vertical
 | line on the top graph. The max(y) value looks OK but the min(y) looks
 | like the second largest value.

Ross Darnell wrote:
> 
> I would like to create a page of two graphs (2 rows by 1 col) and then
> draw vertical lines (segments?) on both graphs from the minimum
> values to the corresponding maximum value.
> 
> So I have tried
> 
> #
> > y <- rnorm(3000)
> > par(mfrow=c(2,1))
> > plot(y,type="l")
> > plot(cumsum(y),type="l")
> > segments(1000,min(cumsum(y)),1000,max(cumsum(y)))
> > par(mfg=c(1,1))
> > segments(1000,min(y),1000,max(y))
> > y <- rnorm(3000)
> 
> The segment looks fine on the bottom graph but I get a small vertical
> line on the top graph. The max(y) value looks OK but the min(y) looks
> like the second largest value.
> 
> > ymin <- min(y)
> > ymax <- max(y)
> > segments(1000,ymin,1000,ymax)
> 
> doesn't make any difference.
OK. The par settings won't be resetted completely, but you can do so
manually:

 y <- rnorm(3000)
 par(mfrow=c(2,1))
 plot(y,type="l")
 rpar <- par()  # remember par settings
 plot(cumsum(y),type="l")
 segments(1000,min(cumsum(y)),1000,max(cumsum(y)))
 par(rpar)      # restore the settings to draw the line 
 par(mfg=c(1,1))
 segments(1000,min(y),1000,max(y), col="red")

In your case it is simpler to complete each plot before stepping to the
next one.

> Can I draw a (one) line that crosses both graphs?
Yes. A simple but rather ugly solution:

  par(xpd = NA)
  abline(v = 1000)

Uwe Ligges