My apologies for what was obviously a simple question (however, I received a
number of replies from others who had the same problem). The SPLUS support
team resolved the problem:
"It is possible to create a grouped bar plot centered on zero with error
bars. Suppose I create the following data in S-PLUS:
my.df <- data.frame(x=LETTERS[1:3], y1=1:3, y2=c(-2,1,2), y3=-3:-1,
z1=c(.3,.6,.9), z2=c(-.4,.2,.8), z3=c(-.7,-.1,-.5))
Then to create the plot, select Graph -> 2D Plot. Choose 'Bar with Error -
Grouped' for the Plot Type and click OK. In the Bar Plot dialog that
appears enter the following information:
Data Set: my.df
x Columns: x
y Columns: y1,y2,y3
z Columns: z1,z2,z3
Click on the Position tab and choose the following:
Bar Base: Zero
Click OK.
You should now have the desired plot.
Following is information on specifying data for a grouped bar chart with
error bars:
For a grouped vertical bar chart with error bars, specify the names or
column numbers of your X, Y, and Z columns. The X column determines the
position of the groups along the x-axis. Each series of bars (for example,
the first bar in each grouping as you move across the graph sheet) must have
a y value corresponding to each x value. Thus the total number of y values
must be the same number of x values multiplied by the number of bars in each
grouping. These y values can be specified with multiple y columns, or with
one long column. The Z column should contain the standard error data and
should have the same dimensions as your Y column(s). Error bars cannot be
automatically calculated for grouped bar charts."
John Payne
UW
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