Hi all, I am a newbie, so maybe my questions are very simple: Question 1. I have negative values after background substraction in a DNA chip data, and I want to discard these values. The data looks like: Gene1 0.3 0.2 0.6 Gene2 0.4 -0.1 1.2 Gene3 1.4 0.4 1.3 And I want: Gene1 0.3 0.2 0.6 Gene2 0.4 NA 1.2 Gene3 1.4 0.4 1.3 Question 2. I have 4 spot for each gene: Gene1_spot1 0.2 0.3 Gene1_spot2 0.3 0.5 Gene1_spot3 0.4 0.5 Gene1_spot4 0.5 0.2 Gene2_spot1 1.3 2.3 How can I calculate the mean of these spots? (mean of spots 1-4 for sample 1, then mean of spots 5-8 etc) Thanks Balazs Gyorffy ___________________________________________________________ BT Yahoo! Broadband - Free modem offer, sign up online today and save ?80 http://btyahoo.yahoo.co.uk