The melt method is powerful and dramatically reshapes your DataFrame. It takes up to five parameters, with two of them being crucial to understanding how to reshape your data correctly:

• id_vars is a list of column names that you want to preserve as columns and not reshape
• value_vars is a list of column names that you want to reshape into a single column

The id_vars, or the identification variables, remain in the same column but repeat for each of the columns passed to value_vars. One crucial aspect of melt is that it ignores values in the index, and, in fact, it silently drops your index and replaces it with a default RangeIndex. This means that if you do have values in your index that you would like to keep, you will need to reset the index first before using melt.