There is provided a method for compressing an index file in an information retrieval system that retrieves information from a plurality of documents. Each of the plurality of documents has features occurring therein. Each of the features has parameters corresponding thereto. Parameter values corresponding to the parameters of the features are mapped into a plurality of bins. Bin identifiers are stored in the index file. Each of the bin identifiers identifies a bin to which is assigned at least one individual parameter value corresponding to at least one individual parameter.