modin.pandas.merge¶

Merge DataFrame or named Series objects with a database-style join.

A named Series object is treated as a DataFrame with a single named column.

The join is done on columns or indexes. If joining columns on columns, the DataFrame indexes will be ignored. Otherwise if joining indexes on indexes or indexes on a column or columns, the index will be passed on. When performing a cross merge, no column specifications to merge on are allowed.

Warning

If both key columns contain rows where the key is a null value, those rows will be matched against each other. This is different from usual SQL join behaviour and can lead to unexpected results.

Parameters:

left (DataFrame or named Series) –
right (DataFrame or named Series) – Object to merge with.
how ({'left', 'right', 'outer', 'inner', 'cross'}, default 'inner') –
Type of merge to be performed.
- left: use only keys from left frame, similar to a SQL left outer join; preserve key order.
- right: use only keys from right frame, similar to a SQL right outer join; preserve key order.
- outer: use union of keys from both frames, similar to a SQL full outer join; sort keys lexicographically.
- inner: use intersection of keys from both frames, similar to a SQL inner join; preserve the order of the left keys.
- cross: creates the cartesian product from both frames, preserves the order of the left keys.
on (label or list) – Column or index level names to join on. These must be found in both DataFrames. If on is None and not merging on indexes then this defaults to the intersection of the columns in both DataFrames.
left_on (label or list, or array-like) – Column or index level names to join on in the left DataFrame. Can also be an array or list of arrays of the length of the left DataFrame. These arrays are treated as if they are columns.
right_on (label or list, or array-like) – Column or index level names to join on in the right DataFrame. Can also be an array or list of arrays of the length of the right DataFrame. These arrays are treated as if they are columns.
left_index (bool, default False) – Use the index from the left DataFrame as the join key(s). If it is a MultiIndex, the number of keys in the other DataFrame (either the index or a number of columns) must match the number of levels.
right_index (bool, default False) – Use the index from the right DataFrame as the join key. Same caveats as left_index.
sort (bool, default False) – Sort the join keys lexicographically in the result DataFrame. If False, the order of the join keys depends on the join type (how keyword).
suffixes (list-like, default is ("_x", "_y")) – A length-2 sequence where each element is optionally a string indicating the suffix to add to overlapping column names in left and right respectively. Pass a value of None instead of a string to indicate that the column name from left or right should be left as-is, with no suffix. At least one of the values must not be None.
copy (bool, default True) – This argument is ignored in Snowpark pandas API.
indicator (bool or str, default False) – If True, adds a column to the output DataFrame called “_merge” with information on the source of each row. The column can be given a different name by providing a string argument. The column will have a Categorical type with the value of “left_only” for observations whose merge key only appears in the left DataFrame, “right_only” for observations whose merge key only appears in the right DataFrame, and “both” if the observation’s merge key is found in both DataFrames.
validate (str, optional) – This is not yet supported.

Returns:

A DataFrame of the two merged objects.

Return type:

DataFrame

See also

merge_ordered: Merge with optional filling/interpolation.
merge_asof: Merge on nearest keys.
DataFrame.join: Similar method using indices.

Examples

>>> df1 = pd.DataFrame({'lkey': ['foo', 'bar', 'baz', 'foo'],
...                     'value': [1, 2, 3, 5]})
>>> df2 = pd.DataFrame({'rkey': ['foo', 'bar', 'baz', 'foo'],
...                     'value': [5, 6, 7, 8]})
>>> df1
  lkey  value
0  foo      1
1  bar      2
2  baz      3
3  foo      5
>>> df2
  rkey  value
0  foo      5
1  bar      6
2  baz      7
3  foo      8

Copy

Merge df1 and df2 on the lkey and rkey columns. The value columns have the default suffixes, _x and _y, appended.

>>> df1.merge(df2, left_on='lkey', right_on='rkey')
  lkey  value_x rkey  value_y
foo        1  foo        5
foo        1  foo        8
bar        2  bar        6
baz        3  baz        7
foo        5  foo        5
foo        5  foo        8

Copy

Merge DataFrames df1 and df2 with specified left and right suffixes appended to any overlapping columns.

>>> df1.merge(df2, left_on='lkey', right_on='rkey',
...           suffixes=('_left', '_right'))
  lkey  value_left rkey  value_right
0  foo           1  foo            5
1  foo           1  foo            8
2  bar           2  bar            6
3  baz           3  baz            7
4  foo           5  foo            5
5  foo           5  foo            8

Copy

>>> df1 = pd.DataFrame({'a': ['foo', 'bar'], 'b': [1, 2]})
>>> df2 = pd.DataFrame({'a': ['foo', 'baz'], 'c': [3, 4]})
>>> df1
     a  b
0  foo  1
1  bar  2
>>> df2
     a  c
0  foo  3
1  baz  4

Copy

>>> df1.merge(df2, how='inner', on='a')
     a  b  c
0  foo  1  3

Copy

>>> df1.merge(df2, how='left', on='a')
     a  b    c
0  foo  1  3.0
1  bar  2  NaN

Copy

>>> df1 = pd.DataFrame({'left': ['foo', 'bar']})
>>> df2 = pd.DataFrame({'right': [7, 8]})
>>> df1
  left
0  foo
1  bar
>>> df2
   right
0      7
1      8

Copy

>>> df1.merge(df2, how='cross')
  left  right
0  foo      7
1  foo      8
2  bar      7
3  bar      8

Copy