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Calculating distance between data and groups

This command can be used to calculate a new data frame containing distances from all data records of a frame to several groups identified by a classified data. The distance can be measured as a) single linkage or b) group-average linkage (see figure below). Single linkage method locates the closest group member, and group-average first evaluates the average point for each group and calculates the distances between these group-averages and all data records. The result is a new data frame containing fields having the names of the groups identified in the classified data.

The calculation complexity of group-average linkage can be much smaller, but it cannot be used with certain types of data distributions. Part c) of the following figure depicts a problematic data distribution for group-average linkage.

figure1469

There is also a local distance model available, in which all distances are limited to located minimum group-to-group distances. These minimum group distances are evaluated using single or group-average linkage according to chosen method.

figure1474

tabular1478

This command creates new fields to a data frame containing distances from data vectors to groups of datavectors within the same data set. The groupings are identified by a classified data structure. The fields in output data are named according to group names.



Erkki Hakkinen
Thu Sep 24 11:51:34 EET DST 1998