Select indexing in merged inverse query evaluations

Embodiments provide for select indexing, which uses an array to simultaneously construct output sets for instructions that operate on input nodesets with common axes. During evaluation of a message against an instruction tree, when a branching node with a large "splay" is iterated over, rather than iterating over an input nodeset with a common axis once per branch, the select indexing described herein iterates over the nodeset once in total. More specifically, the select index data structure includes an array of empty node sets for instructions that both, branch from a branching node, and evaluate input nodes that share a common axis. Identifiers for the input nodeset are compared to indices within the select index, and matches for the input nodes are added to the corresponding nodeset for the appropriate instruction. The results of the evaluation may then be passed to the branches of the select instructions for further processing.