Re-indexing in pandas is a process that makes the data in a Series conform to a set of labels. It is used by pandas to perform much of the alignment process and is hence a fundamental operation.
Re-indexing achieves several things:
- Re-ordering existing data to match a set of labels
- Inserting NaN markers where no data exists for a label
- Possibly filling missing data for a label using some type of logic (defaulting to adding NaN values)
Re-indexing can be as simple as simply assigning a new index to the .index property of a Series. The following demonstrates changing the index of a Series in this manner: