The operation selects classes from a source classified data to a target classified data. Because the names in the expression refers to a data frame, the source classified data have to correspond to this data frame. In other words, there must be a class in the source classified data for each data record referred from the expression.
The flag -empty defines, if empty classes are created for each class in the source classified data anyway. Another alternative is to pick only those classes that are matched from the expression. See more about expressions in Section 4.2.1.
Example (ex4.6): Because a TS-SOM has several layers, it is often necessary to pick one of them, for instance, to use the selected layer as a classifier. The following commands show a piece of such commands:
# do typical sequence for training SOM (som), # for creating SOM classification (cld), # and so forth ... # take SOM layer indexes to a field NDA> somlayer -s som -fout somlay # selected classes from the layer 3 NDA> selcld -c cld -cout cld3 -expr 'somlay' = 3; -empty ...