[R] Error bars.

[Michael Camann]

Rolf et al.--

Here's a simple error bar function in R.

# produce vertical error bars on a plot-- aliased vbars in anticipation
# of the day when I need hbars to plot horizontal error bars....
#
# error bars originate at (x, y0) and radiate to y0 + y1 and y0 - y2
#
# example (adds +- 1.0 SE to a barplot of means for data vector x):
#
# y.mean <- mean(x)				# mean
# y.se <- sqrt(var(x,na.rm=TRUE)/length(x))	# std err
# z <- barplot(y.mean,plot=FALSE)		# location of bars
# barplot(y.mean,...)				# the real plot
# ebars(z,y.mean,y.mean+y.se,y.mean-y.se)	# add error bars


ebars <- vbars <- function (x, y0, y1, y2)
{
  for(i in 1:length(x))
  {
    if(y0[i]!=0 & !is.na(y0[i]) & y1[i]!=0 & !is.na(y1[i]) &
      (y0[i]!=y2[i]))
    {
      arrows (x[i], y0[i], x[i], y1[i], angle=90, length=0.05)
    }
    if(y0[i]!=0 & !is.na(y0[i]) & y2[i]!=0 & !is.na(y2[i]) &
      (y0[i]!=y2[i]))
    {
      arrows (x[i], y0[i],  x[i], y2[i],  angle=90, length=0.05)
    }
  }
}

--Mike C.

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Michael A. Camann                                  Voice: 707-826-3676
Associate Professor of Zoology                       Fax: 707-826-3201
Institute for Forest Canopy Research     Email: mac24 at axe.humboldt.edu
Department of Biology                            ifcr at axe.humboldt.edu
Humboldt State University
Arcata, CA 95521

                 URL:http://www.humboldt.edu/~mac24/
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


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