How to deal with large data sets
Welcome! I think you asked in the right place.  

If you have familiarity with Python, you might look at the numpy and Pandas libraries.  Numpy implements fast array and matrix manipulations, and Pandas arranges numpy objects into tables.  Along with scipy, they make the basis of the Python numerical computing stack.

Without more detail it's difficult to share a code example that'll do what you want, but if you run into any issues feel free to ask.

Edit: if your dataset is REALLY big and won't fit in memory, there are ways around that too, just specify.