DataFrame.join(other, on=None, how='left', lsuffix='', rsuffix='', sort=False)
[source]
Join columns with other DataFrame either on index or on a key column. Efficiently Join multiple DataFrame objects by index at once by passing a list.
Parameters: |
other : DataFrame, Series with name field set, or list of DataFrame Index should be similar to one of the columns in this one. If a Series is passed, its name attribute must be set, and that will be used as the column name in the resulting joined DataFrame on : column name, tuple/list of column names, or array-like Column(s) in the caller to join on the index in other, otherwise joins index-on-index. If multiples columns given, the passed DataFrame must have a MultiIndex. Can pass an array as the join key if not already contained in the calling DataFrame. Like an Excel VLOOKUP operation how : {‘left’, ‘right’, ‘outer’, ‘inner’}, default: ‘left’ How to handle the operation of the two objects.
lsuffix : string Suffix to use from left frame’s overlapping columns rsuffix : string Suffix to use from right frame’s overlapping columns sort : boolean, default False Order result DataFrame lexicographically by the join key. If False, preserves the index order of the calling (left) DataFrame |
---|---|
Returns: |
joined : DataFrame |
See also
DataFrame.merge
on, lsuffix, and rsuffix options are not supported when passing a list of DataFrame objects
>>> caller = pd.DataFrame({'key': ['K0', 'K1', 'K2', 'K3', 'K4', 'K5'], ... 'A': ['A0', 'A1', 'A2', 'A3', 'A4', 'A5']})
>>> caller A key 0 A0 K0 1 A1 K1 2 A2 K2 3 A3 K3 4 A4 K4 5 A5 K5
>>> other = pd.DataFrame({'key': ['K0', 'K1', 'K2'], ... 'B': ['B0', 'B1', 'B2']})
>>> other B key 0 B0 K0 1 B1 K1 2 B2 K2
Join DataFrames using their indexes.
>>> caller.join(other, lsuffix='_caller', rsuffix='_other')
>>> A key_caller B key_other 0 A0 K0 B0 K0 1 A1 K1 B1 K1 2 A2 K2 B2 K2 3 A3 K3 NaN NaN 4 A4 K4 NaN NaN 5 A5 K5 NaN NaN
If we want to join using the key columns, we need to set key to be the index in both caller and other. The joined DataFrame will have key as its index.
>>> caller.set_index('key').join(other.set_index('key'))
>>> A B key K0 A0 B0 K1 A1 B1 K2 A2 B2 K3 A3 NaN K4 A4 NaN K5 A5 NaN
Another option to join using the key columns is to use the on parameter. DataFrame.join always uses other’s index but we can use any column in the caller. This method preserves the original caller’s index in the result.
>>> caller.join(other.set_index('key'), on='key')
>>> A key B 0 A0 K0 B0 1 A1 K1 B1 2 A2 K2 B2 3 A3 K3 NaN 4 A4 K4 NaN 5 A5 K5 NaN
© 2011–2012 Lambda Foundry, Inc. and PyData Development Team
© 2008–2011 AQR Capital Management, LLC
© 2008–2014 the pandas development team
Licensed under the 3-clause BSD License.
http://pandas.pydata.org/pandas-docs/version/0.19.2/generated/pandas.DataFrame.join.html