Lessons in efficiency while coding Perl:

• Use regular expressions to split tab-delimited fields in large data files.
• Minimize number of elements in arrays and hashes.
• Use indexing variables.
• Use seek function rather than iteratively reading through filelines

Lessons in efficiency while coding R:

• Avoid loops; use sapply (or variant thereof).
• Label row names and column names of data frames for ease of subsetting.
• Download packages that have useful functions instead of attempting to reinvent the wheel.