summaryHeaderFromFieldHeader

Produce a summary header from a field header.

The result has the form <fieldHeader>_<operation>. e.g. If the field header is "length" and the operation is "max", the summary header is "length_max". The field header typically comes a header line in the input data or was constructed by fieldHeaderFromIndex().

If operationName is the empty string, then fieldHeader is used unchanged. This supports the Retain operator.