Melting a Pandas DataFrame from Wide to Long Format Twice on the Same Column

Converting Long Data Frames to Longer Data Frames with Running Indicators in R

Reshaping Long-Form Data with Pandas: A Comparison of Two Methods

Using Custom Aggregate Functions with cast() in R reshape2: A Practical Guide to Resolving the Limitation of vapply and fill=0

Reshape and Group by Operations in Pandas DataFrames: A Comparative Approach