Numerical Computing with Python

Understanding the differences between concat, join, and merge

The merge and join DataFrame (and not Series) methods and the concat function all provide very similar functionality to combine multiple pandas objects together. As they are so similar and they can replicate each other in certain situations, it can get very confusing when and how to use them correctly. To help clarify their differences, take a look at the following outline:

• concat:
  • Pandas function
  • Combines two or more pandas objects vertically or horizontally
  • Aligns only on the index
  • Errors whenever a duplicate appears in the index
  • Defaults to outer join with option for inner
• join:
  • DataFrame method
  • Combines two or more pandas objects horizontally
  • Aligns the calling DataFrame's ...