Continuous Group Variables

The BOXPLOT Procedure

Continuous Group Variables

By default, the PLOT statement treats numerical group variable values as discrete values and spaces the boxes evenly on the plot. The following statements produce the plot shown in Figure 18.5:

   symbol v=dot c=salmon;
   goptions ftext=swiss;
   axis1 minor=none color=black label=(angle=90 rotate=0);
   title 'Box Plot for Power Output';

   proc boxplot data=turbine;
      plot kwatts*day / turnhlabel
                        cframe   = vligb
                        cboxes   = dagr
                        cboxfill = ywh
                        vaxis    = axis1;
   run;

The labels on the horizontal axis in Figure 18.5 do not represent 20 consecutive days, but the box-and-whisker plots are evenly spaced (note that the TURNHLABEL option orients the horizontal axis labels vertically so there is room to display them all).

Figure 18.5: Box Plot with Discrete Group Variable

In order to treat the group variable as continuous, you can specify the CONTINUOUS or HAXIS= option. Either option produces a box plot with a horizontal axis scaled for continuous group variable values.

The following statements produce the plot shown in Figure 18.6. Note that the values on the horizontal axis represent consecutive days. Box-and-whisker plots are not produced for days when no turbine data was collected. The TOTPANELS= option is specified to display the entire box plot on one panel.

   symbol v=dot c=salmon;
   title 'Box Plot for Power Output';
   axis1 minor=none color=black label=(angle=90 rotate=0);

   proc boxplot data=turbine;
      plot kwatts*day / turnhlabel
                        cframe    = vligb
                        cboxes    = dagr
                        cboxfill  = ywh
                        totpanels = 1
                        vaxis     = axis1
                        continuous;

   run;

Figure 18.6: Box Plot with Continuous Group Variable

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