A method and system for mapping a number of characters in a string, wherein the string comprises a combination of characters representing indexed expressions and a combination of characters representing non-indexed expressions. One embodiment produces a weight array that can be utilized to compare a first and second string having indexed and non-indexed expressions. In one embodiment, a method generates a set of special weights for characters that represent indexed and non-indexed expressions. The method then associates a weight value of an indexed expression with the specific group of characters representing a specific non-indexed expression, and generates a weight array by retrieving a plurality of special weights associated with the specific group of characters representing the specific non-indexed expression and the associated weight value of the indexed expression.