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error bars in line plots

6 messages · Myriam Abramson, Ko-Kang Kevin Wang, Ott Toomet +3 more

Myriam Abramson
# 
Hi!

Could you tell me how I can draw a graph with error bars? 
Sorry, I don't use R that often and I couldn't find it easily in the
documentation. 

TIA
Ko-Kang Kevin Wang
# 
Hi,

Take a look at http://finzi.psych.upenn.edu/R/Rhelp02/archive/4124.html and
its thread.

You may want to bookmark Jonathan Baron's page,
http://finzi.psych.upenn.edu/search.html , which lets you search the r-help
archive and R documentations.  You can find more information about error
bars there.

Hope this helps,

Kevin

------------------------------------------------
Ko-Kang Kevin Wang
Post Graduate PGDipSci Student
Department of Statistics
University of Auckland
New Zealand
www.stat.auckand.ac.nz/~kwan022

----- Original Message -----
From: "Myriam Abramson" <mabramso at gmu.edu>
To: <r-help at stat.math.ethz.ch>
Sent: Sunday, October 06, 2002 5:09 PM
Subject: [R] error bars in line plots
-.-.-
http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
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Ott Toomet
#
On 6 Oct 2002, Myriam Abramson wrote:
|Hi!
  |
  |Could you tell me how I can draw a graph with error bars? 
  |Sorry, I don't use R that often and I couldn't find it easily in the
  |documentation. 

There is no errorbars function in the package.  But you may easily construct
your own using segments().  I add my own versions below (actually, why not
put something similar into the base package?).

You may use it as:
plot(x,y)
errorbars(x,y, dy=dy)

The second function is for using with matplot().

Ott

-----------------------

errorbars <- function(x, y, dy=NULL, dx=NULL, ...) {
  if(dy) {
    segments(x, y-dy, x, y+dy, ...)
  }
  if(dx) {
    segments(x-dx, y, x+dx, y, ...)
  }
}


materrorbars <- function(x, y, dy=NULL, dx=NULL,
                         col=par("col"), lty=par("lty")) {
  M <- ncol(y)
  if(is.matrix(x))
    N <- nrow(x)
  else {
    N <- length(x)
    x <- matrix(x, N, M)
  }
  karv <- rep(col, length.out=M)
  joon <- rep(lty, length.out=M)
  if(!is.null(dy)) {
    for(i in seq(M)) {
      segments(x[,i], y[,i]-dy[,i], x[,i], y[,i]+dy[,i],
               col=karv[i], lty=joon[i])
    }
  }
  if(!is.null(dx)) {
    for(i in seq(M)) {
      segments(x[,i]-dx[,i], y[,i], x[,i]+dx[,i], y[,i],
               col=karv[i], lty=joon[i])
    }
  }
}

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volker.franz@tuebingen.mpg.de
# 
Hi, 

    >> Could you tell me how I can draw a graph with error bars?
KKW> Hi, Take a look at
    KKW> http://finzi.psych.upenn.edu/R/Rhelp02/archive/4124.html and
    KKW> its thread.

I just had a look at this page and expanded the examples a bit:

##Sample data:
mydat <- data.frame(x=1:10, y=1:10, dy=rnorm(10))
attach(mydat)

##Style of errorbars:
myangle=90  #Angle from shaft to edge of arrow head.
mylength=0.2#Length of arrow head in inches (!!!)

##One--sided errorbars:
plot(x,y,ylim=range(y,y+dy))
arrows(x,y,x,y+dy,angle=myangle,length=mylength)

##Two--sided errorbars:
plot(x,y,ylim=range(y-dy,y+dy))
arrows(x,y-dy,x,y+dy,code = 3,angle=myangle,length=mylength)

HTH
Volker
Frank E Harrell Jr
# 
On Mon, 7 Oct 2002 09:23:08 +0200 (CEST)
Ott Toomet <siim at obs.ee> wrote:

            

      
      
      
    

        
. . .

Also look at errbar and xYplot in the Hmisc library.  -Frank Harrell

  
    

      
      
    

  


  


      

    

    

      
      

        


  

        

      Richard Rowe
    

    

      
      #
    

  


  

      
At 09:23 07/10/02 +0200, you wrote:

            

      
      
      
    

        
When I first met the problem I felt error bars should be added ... however 
different disciplines have different ideas on what confidence intervals 
should be and a 'packaged' version of 'error bars' may be less than 
helpful.  Maybe a short script should be put somewhere accessable?  I built 
my own script in a couple of minutes based on previous solutions given by 
readers of r-help ... . It is actually a nice beginner exercise in R 
programming, taking a few moments with every prospect of swift success,


Richard Rowe
Senior Lecturer
Department of Zoology and Tropical Ecology, James Cook University
Townsville, Queensland 4811, Australia
fax (61)7 47 25 1570
phone (61)7 47 81 4851
e-mail: Richard.Rowe at jcu.edu.au
http://www.jcu.edu.au/school/tbiol/zoology/homepage.html

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