Order the Levels of a Categorical Variable

The levels of a categorical (nominal or ordinal) variable on axes are ordered using the Value Ordering column property (if one has been assigned), or the default value ordering. To change the ordering, you can either:

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Use the Value Ordering column property. For details about the Value Ordering column property, see Value Ordering in the Using JMP book.

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Use the values of a numeric variable already in the graph. In Graph Builder, right-click on the categorical axis and select Order By.

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Use the values of an arbitrary numeric variable. In Graph Builder, drag the numeric variable next to the categorical variable in the zone until a trapezoid appears, then drop the variable. The axis label changes to <categorical variable> ordered by <numeric variable>. See Example of Ordering the Levels of a Categorical Variable Using a Numeric Variable.

To change the order of the levels or the statistic, proceed as follows:

Right-click on the axis label and select Order By.

Select one of the ascending or descending options.

You can order by a variable’s Order Statistic (these options are prefixed by the variable’s name) or by the number of observations in each level of the categorical variable (Count).

The default ordering statistic is the mean. To use another statistic, right-click on the axis label and select Order Statistic.

Note: If you try to order the values of a numeric variable using another numeric variable, JMP merges the variables. See Merge Variables on a Common Axis.

Example of Ordering the Levels of a Categorical Variable Using a Numeric Variable

To order a nominal or ordinal variable by a numeric variable, consider data about vehicle types. You want to see the vehicle types arranged in a meaningful order.

Select Help > Sample Data Library and open Cars.jmp.

Select Graph > Graph Builder.

Select Size and drag it into the X zone.

This variable represents the type of the vehicle. Eight levels are listed alphabetically on the X axis: compact (comp), heavy (hev), lightweight (lt), medium (med), mini, multi-purpose (mpv), pick-up truck (pu), and van. Since the levels are listed alphabetically, they are not ordered in a meaningful way. For example, heavy comes before mini and lightweight. You want to order the levels by Wt (weight).

Select Wt and drag it to the middle of the X axis. Drop it just above the X axis. Before you drop the variable, a blue quadrilateral appears.

Merging Wt and Size

The levels of Size are now arranged in increasing order according to the average Wt of all vehicles in the levels. Notice that mini and lt (lightweight) are now ordered before hev (heavy). The axis label is updated, signifying that an ordering variable is in use.

Next, verify that Size is actually ordered by Wt.

Select Wt and drag it to the Y zone.

Select Mean from the Summary Statistic list.

Example of Size Ordered by Wt, Ascending