Yes, in fact I use excel to replace empty fields with another value (-999). But I would like to avoid this "manual" step. For example, I am using IDL to read the text file. Let's say that I have the following matrix:
10 20 33 45
21 14 e 78
(where "e" means empty value). If I read the first row, IDL identifies a vector with 4 components, and the value for column 3 will be 33. When I read the second row, IDL identifies a vector with 3 components, and the value for column 3 will be 78. May be the issue is how to identify empty values with IDL...