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