datatable.join()

datatable.

join

(

frame

)

sourcetests

Join clause for use in Frame’s square-bracket selector.

This clause is equivalent to the SQL JOIN, though for the moment datatable only supports left outer joins. In order to join, the frame must be keyed first, and then joined to another frame DT as:

DT[:, :, join(X)]

provided that DT has the column(s) with the same name(s) as the key in frame.

Parameters

frame

Frame

An input keyed frame to be joined to the current one.

return

Join Object

In most of the cases the returned object is directly used in the Frame’s square-bracket selector.

except

ValueError

The exception is raised if frame is not keyed.

See Also

• Tutorial on joins

Examples

df1 = dt.Frame(""" date X1 X2 01-01-2020 H 10 01-02-2020 H 30 01-03-2020 Y 15 01-04-2020 Y 20""") df2 = dt.Frame("""X1 X3 H 5 Y 10""")

First, create a key on the right frame (df2). Note that the join key (X1) has unique values and has the same name in the left frame (df1):

df2.key = "X1"

Join is now possible:

df1[:, :, join(df2)]

	date	X1	X2	X3
	str32	str32	int32	int32
0	01-01-2020	H	10	5
1	01-02-2020	H	30	5
2	01-03-2020	Y	15	10
3	01-04-2020	Y	20	10

4 rows × 4 columns

You can refer to columns of the joined frame using prefix g., similar to how columns of the left frame can be accessed using prefix f.:

df1[:, update(X2=f.X2 * g.X3), join(df2)] df1

	date	X1	X2
	str32	str32	int32
0	01-01-2020	H	50
1	01-02-2020	H	150
2	01-03-2020	Y	150
3	01-04-2020	Y	200

4 rows × 3 columns