A system and method for determining the composition of a sample is provided. The system and method according to the present invention comprises: obtaining one or more spectra of the sample; obtaining one or more spectra of one or more target materials; pre-process the sample and the target spectra; providing a variable reduction means that combines certain contiguous spectral variables into a single variable, wherein the intensities of the said single variable is the sum of the intensities of the said spectral variables to be combined; determining an average spectrum and the statistic distribution of the sample and/or each of the target material in the reduced dimension; determining the likelihood the sample had the same composition of each of the one or more target material; and displaying the list of the most likely target material to a user.