BarChart - Extendng the Y-axis and labeling the endpoints

*To*: mathgroup at smc.vnet.net*Subject*: [mg97536] BarChart - Extendng the Y-axis and labeling the endpoints*From*: Donald DuBois <donabc at comcast.net>*Date*: Sat, 14 Mar 2009 18:16:30 -0500 (EST)

Here is a BarChart (almost directly from the Mathematica Documentation): Needs["BarCharts`"] thisBarChart = BarChart[{1, 2, -1.3, 2.4}] I am trying to extend the labeling of the Y-axis so that the endpoints of the Y-axs extend a little beyond the extremes of the data in the Y direction (the extremes of the data being -1.3 and 2.4) and these endpoints are labeled with multiples of the chosen increment. I believe this makes the BarChart easier to read and is aesthetically more pleasing. For example, with the above evaluation of BarChart, the labeling of the Y-axis goes from 2.0 to -1.0 in increments of 0.5 as chosen by Mathematica but the Y-axis itself extends beyond these labels. I would like to extend the labeling in both directions (positive and negative sides along the Y-axis) to the nearest integral multiple of the increment that Mathematica has chosen so the Y-axis would be extended slightly beyond the extremes of the data and the endpoints of the Y-axis would have labels. In this example, the Y-axis would be extended from 2.5 to -1.5 and the labeling would go from { -1.0, -0.5, 0.0, 0.5, 1.0, 1.5, 2.0} to {-1.5, -1.0, -0.5, 0.0, 0.5, 1.0, 1.5, 2.0, 2.5} with the labeling being integral multiples of the chosen increment. To do this, I need to know that the automatic labeling is in increments of 0.5 (as chosen by Mathematica) and then I need to extend the endpoint labels from {-1.0, 2.0} to {-1.5, 2.5}. I can get the PlotRange that is chosen by Mathematica automatically by using AbsoluteOptions on the graphical object called thisBarChart: AbsoluteOptions[thisBarChart, PlotRange] which produces {PlotRange -> {{0.4, 4.6}, {-1.3, 2.4}}} But, I still don't know the increment that Mathematica used so that I can force the labeling to a high of 2.5 and a minimum of -1.5. There's another complication: Assuming I did know (by magic) that the chosen increment was 0.5 for the labeling I thought I could then use BarChart[{1, 2, -1.3, 2.4}, PlotRange -> {Automatic, { 2.5, -1.5}}] to extend the Y-axis endpoints with labels of -1.5, and 2.5 but this doesn't work because the endpoints of the Y-azis are not labeled. I find, through experimentation only, that what I need is: BarChart[{1, 2, -1.3, 2.4}, PlotRange -> {Automatic, {3.0, -2.0}}] and the increment for the labeling has automatically changed to 1 (the fact that the increment has changed from 0.5 to 1.0 in this case is not a problem.) How can I get Mathematica to do this in a programmatic way so that I don't need to experiment each time to (1) get the Y-axis extended a little beyond the extremes of the data and (2) the endpoints labeled with integral multiples of the chosen increment? Thank you in advance for any help you can give me.

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