In COMPSTAT'98 article , Klaschka and Mola dealt with an economical way of calculating, in the tree-based methods, all the values of splitting criterion for the splits based on an -valued categorical variable. We proposed a specific ordering of splits suitable for recalculating one value from another.
The core of the paper was a combinatorial idea: The -tuples of 's and 's coding the splits can be ordered in a sequence so that any two successive elements differ in exactly one position.
Only later I learned that the same combinatorial idea had already been utilized as early as in the sixties in the all possible subsets regression, see , .
Moreover, even in the sixties the idea was not quite novel: It was an independent reinvention of so called Gray code, for which Frank Gray took out a patent in 1953 (see , ).
Gray code seems to possess a high potential of being repeatedly reinvented. By the way, Gray was not the first to invent it: According to , it was used by Emile Baudot's telegraph, awarded a gold medal at the Universal Exposition in Paris in 1878.