Common code dictionary

Create a dictionary for common used code in analyzing NMDX dataset

Look at existing Jupyter notebooks in the repository to understand the NMDX dataset analysis workflow. Identify frequently used code snippets, functions, or patterns. Create a dictionary (likely a markdown or text file) that lists these common code pieces with explanations. Check if there's a docs or resources folder to place the dictionary.

Written by the indexing model from the issue text.