[R] adding SE to bar plots

Anne York york at noaa.gov
Mon Nov 25 18:27:14 CET 2002

This simple function was written to superimpose error bars on a scatter
plot but can be also used with simple barplots. See second example.

"superpose.eb" <- function (x, y, ebl, ebu = ebl, lh = 0.01,   ...) 
#function to add error bars to an existing scatterplot
#written by Anne York, May 2002
#ebu is the length of the upper error bar; assumed to be a vector with same
#                                          length of x and y
#ebl is the length of the lower error bar; assumed to be a vector with same
#                                          length of x and y
#2*lh is a the length of the tick at the end of the error bar
#it is assumed that the limits of the axes on the existing plot are 
#sufficiently large to accomodate the error bars.

    segments(x, y + ebu, x, y - ebl, ...)
    segments(x - lh , y + ebu, x + lh , y + ebu, 
    segments(x - lh, y - ebl, x + lh , y - ebl,  ...)

my.ebl <- 2*abs(rnorm(10))
plot(1:10,1:10,ylim = c((0-max(ebl)),10+max(ebl)))
superpose.eb(1:10,1:10,ebl=my.ebl, lh = 0.05)

#Also works with a simple barplot:
dum <- barplot(1:10,ylim=c(0,12))
my.ebu <- abs(rnorm(10))
superpose.eb(dum[,1],1:10,ebl = 0, ebu=my.ebu, lh = 0.1, lwd = 3, col
points(dum[,1],1:10,pch=16, col = "red") # covers up the lower tick mark 

Date: Tue, 19 Nov 2002 15:28:56 -0800
From: Bill Shipley <Bill.Shipley at Usherbrooke.ca>
Subject: [R] adding SE to bar plots

Hello.  I know that one can add standard errors to a bar plot by repeated 
use of the lines() function, but this can be long when there are many 
bars.  I wonder if there is not already some other function that does this 

Bill Shipley
Departement de biologie
Universite de Sherbrooke
Sherbrooke (Quebec) CANADA J1K 2R9
Bill.Shipley at USherbrooke.ca

Anne E. York
National Marine Mammal Laboratory
Seattle WA 98115-0070  USA
e-mail: anne.york at noaa.gov
Voice: +1 206-526-4039
Fax: +1 206-526-6615

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