Thanks for your suggestions. I have noticed that you have mentioned in previous thread that a set of arrays is a poor choice of data structures. Honestly speaking, I find the Data structures in perl (like arrays of arrays, hashes of arrays, arrays of hashes etc.) very complicated for my understanding because of diverse use of parentheses & brackets and because of my recent introduction to perl as a biologist. Perl is the first computer language that I have been trying to learn through personal endeavor. I donot have any formal training on computer and its applications. I hope you will understand my limitations in understanding a computer language. Moreover, it may sound strange that I started learning how to use a computer(a laptop) since 22nd February 2008 when I was given a laptop by the university. Prior to that I could not afford a laptop because of its high cost.