ClassifyNonzeroEqualCount - ObjectVision/GeoDMS GitHub Wiki

Classify functions ClassifyNonzeroEqualCount

• ClassifyNonzeroEqualCount(a, domain_unit)
• ClassifyNonzeroEqualCount(values, count, domain unit)

Since GeoDMS 20.20.0 the second form classifies a value-count table that was calculated before, with values and count the two subitem of a weeded_counts result. Use it when more than one result is derived from the same scan of a, since the calculation cache then calculates that scan once; the GeoDMS GUI uses this form of ClassifyNonzeroJenksFisher for the classification it generates for a map layer without a configured Classification. Below 4096 distinct values it gives the same class breaks as the two argument form; above it they can differ, because weeded_counts merges values that the two argument form counts separately.

ClassifyNonzeroEqualCount(a, domain unit) results in a data item with class breaks based on an equal count distribution of classes, as ClassifyEqualCount does, but treats the value 0 as a special value, as ClassifyNonzeroJenksFisher does (since 20.23.1):

• 0 is a compulsory class break, and the class that starts at 0 contains only the zeros.
• The negative and the positive values are classified separately, each with an equal count distribution over its own values.
• The numbers of classes for the negative and the positive values, within the total number of classes, are chosen such that the largest average count of a class is as small as possible. On a tie, the positive values get the extra class.

With 2 classes and data that contain negative values, the value 0 and positive values, there is no room for a class of 0 alone: the class breaks are the minimum and 0, so the negative values form the first class, and 0 shares the second class with the positive values.

Data with negative and positive values but without the value 0 also get a class break at 0 when there are 3 or more classes. The class that starts at 0 then contains no values, so that a diverging palette is centred on 0.

With only positive or only negative values, with 1 class, or with no more distinct values than classes, the class breaks are those of ClassifyEqualCount.

The same function can also be applied from the GUI, by requesting the Palette Editor of a map layer and activating the Classify > Equal Counts non-zero classification (since 20.23.1).

The ClassifyNonzeroEqualCount results in a set of ClassBreaks that can be used in the classify function to classify a data item.

attribute<nrPersons> classifyNZEcNrInh (inh_4K) := ClassifyNonzeroEqualCount(NrInh, inh_4K);

Table inh_4K, nr of rows = 4

Table District, nr of rows = 15

The value 0 gets a class of its own, and the 13 positive values are divided over the other 3 classes with counts as equal as possible. On the same data, ClassifyEqualCount gives the class breaks 0, 55, 300 and 860.

• ClassifyEqualCount
• ClassifyNonzeroEqualInterval
• ClassifyNonzeroJenksFisher