1. A computer apparatus, comprising: a processor; a memory communicatively coupled to the processor and storing program instructions causing the processor to: receive a user-defined query comprising one or more numerical data constraints; determine the relevancy of the query to each of one or more entries in a computer-searchable electronic index, each of the index entries representing an item of data extracted from at least one of a plurality of electronic source documents, wherein the determining further comprises: determine a spectral vector for at least a part of the query across the plurality of electronic source documents, the spectral vector comprising a first column of binned numerical values associated with the query and a second column of frequencies of occurrence of the binned numerical values within the plurality of electronic source documents, identify at least one spectral feature comprising a local maximum or local minimum in the frequencies of occurrence within the spectral vector, and limit the computer-searchable electronic index to those documents of the plurality of electronic source documents that are associated with the at least one spectral feature, the relevancy being based on association of documents with the at least one spectral feature; generate a graph, based on the relevancy determination, comprising a separate data point for each of the index entries determined to be most relevant to the query, wherein a plurality of the most relevant index entries can be extracted from a single one of the source documents; and provide an interactive display of the graph.