Final answer:
The provided code snippet indicates an outer join operation between two dataframes on a common column in a data analysis library. It results in a combined dataframe with all records from both original dataframes and nulls for any unmatched records.
Step-by-step explanation:
The notation (adf, bdf, how='outer', on='x1') appears to be referring to a command or function call that is likely used in a programming context, specifically in data manipulation or data analysis libraries such as pandas in Python. This command suggests a merge or join operation between two dataframes, 'adf' and 'bdf', on a common column 'x1' using an outer join. An outer join combines the rows from both dataframes where the join condition is met and also includes all other rows from both dataframes, with missing values filled in as null where no match is found.
For example, if 'adf' has rows with keys 1, 2, and 3 in column 'x1', and 'bdf' has rows with keys 1, 3, and 4, the outer join on 'x1' would result in a dataframe containing keys 1, 2, 3, and 4, with the respective data from each original dataframe included where a match is found and nulls elsewhere.