Concatenating DataFrames

While merge combines DataFrames by matching columns, concat stacks them together.

Stack rows (vertical):

combined = pd.concat([df1, df2, df3])

Useful for combining monthly files into one dataset.

Stack columns (horizontal):

combined = pd.concat([df1, df2], axis=1)

Reset the index after concatenating:

combined = pd.concat([df1, df2], ignore_index=True)

Without ignore_index, you'll have duplicate index values from each original DataFrame.

I cover data combination techniques in my Pandas course.