[R] Error bars on barplots

Martin Maechler maechler at stat.math.ethz.ch
Tue Sep 14 17:17:30 CEST 1999

>>>>> On Tue, 7 Sep 1999 12:24:38 GMT+2, "Karen KOTSCHY" <karen at gecko.biol.wits.ac.za> said:

    Karen> Hi everyone I've finally had a chance to look at this problem
    Karen> again. Thanks to Paul Murrell and Bendix Carstensen, putting
    Karen> error bars on barplots with single bars is quite simple, as
    Karen> barplot returns the x locations of the bar midpoints.

    Karen> However... with plots where you have groups of bars (where x is
    Karen> a matrix and beside=T), it is not as simple. One can work out
    Karen> the x locations of each individual bar manually, knowing the bar
    Karen> width and the midpoint of the group. I've written a function to
    Karen> do this when there are 3 bars in a group (see below). I'm sure
    Karen> the R gurus out there could suggest a more elegant or a simpler
    Karen> way!


    Karen> ----------------------------
    Karen> Karen Kotschy Centre for Water in the Environment University of
    Karen> the Witwatersrand Johannesburg

I've changed  barplot() to
- accept a "plot = FALSE" argument (default remains TRUE)
- in the above case ``beside = TRUE'' return 
  a vector of locations for *each* bar 
  (instead of midpoints of group of "beside-bar"s)

I wonder if we shouldn't even return a matrix of these locations
with the same dimension as  the barplot matrix argument.
This matrix result could still be addressed as a vector (as all
matrices can), but additionally, one could also use  apply(<res>, 2, mean)
to get the locations of the mids of each bar group.


Martin Maechler <maechler at stat.math.ethz.ch>	http://stat.ethz.ch/~maechler/
Seminar fuer Statistik, ETH-Zentrum  LEO D10	Leonhardstr. 27
ETH (Federal Inst. Technology)	8092 Zurich	SWITZERLAND
phone: x-41-1-632-3408		fax: ...-1228			<><
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