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Left Join
course content

Course Content

Data Manipulation using pandas

Left JoinLeft Join

Let's start with left and right joins. What does left join mean? Left join returns all the records from the left table, and matching records from the right table. If not all the records were matched, than remaining fields would be filled with NAs.

Implementation in Python

All types of joins are implemented in pandas with the df_left.merge(df_right, on = 'column', how = 'method') function. There df_left is the left table, df_right is the right one, on - key field (column) that will be used for comparison, how - type of join.

For instance, let's perform a left join of two dataframes. Column with unique values in each dataframe is id. To perform a left join, set the how = 'left' parameter.

Left Join

As you can see, all the records from the data1 table were left, and only matching record from the data2 table were added.

Everything was clear?

Section 5. Chapter 2