The rows from multiple DataFrame objects can be concatenated to each other using the pd.concat() function and by specifying axis=0. The default operation of pd.concat() on two DataFrame objects along the row axis operates in the same way as the .append() method.
This is demonstrated by reconstructing the two datasets from the earlier append example and concatenating them instead.
If the set of columns in all DataFrame objects is not identical, pandas will fill those values with NaN.
Duplicate index labels can result as the rows are copied verbatim from the source objects. The keys parameter can be used to help differentiate which data frame a set of rows originated from. The following demonstrates by using keys to add a level to the index representing the source object:
