datatable.sort()

datatable.

sort

(

*cols

,

reverse=False

,

na_position="first"

)

source

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

When a sort() object is present inside a DT[i, j, ...] expression, it will sort the rows of the resulting Frame according to the columns cols passed as the arguments to sort().

When used together with by(), the sort clause applies after the group-by, i.e. we sort elements within each group. Note, however, that because we use stable sorting, the operations of grouping and sorting are commutative: the result of applying groupby and then sort is the same as the result of sorting first and then doing groupby.

When used together with i (row filter), the i filter is applied after the sorting. For example:

DT[:10, :, sort(f.Highscore, reverse=True)]

will select the first 10 records from the frame DT ordered by the Highscore column.

Parameters

cols

FExpr

Columns to sort the frame by.

reverse

bool

If False, sorting is performed in the ascending order. If True, sorting is descending.

na_position

None | "first" | "last" | "remove"

If “first”, the default behavior, missing values are placed first in sorted output. If “last”, they are placed last. If “remove”, rows that contain missing values in cols are excluded from the output.

return

object

datatable.sort object for use in square-bracket selector.

Examples

from datatable import dt, f, by DT = dt.Frame({"col1": ["A", "A", "B", None, "D", "C"], "col2": [2, 1, 9, 8, 7, 4], "col3": [0, 1, 9, 4, 2, 3], "col4": [1, 2, 3, 3, 2, 1]}) DT

	col1	col2	col3	col4
	str32	int32	int32	int32
0	A	2	0	1
1	A	1	1	2
2	B	9	9	3
3	NA	8	4	3
4	D	7	2	2
5	C	4	3	1

6 rows × 4 columns

Sort by a single column:

DT[:, :, dt.sort("col1")]

	col1	col2	col3	col4
	str32	int32	int32	int32
0	NA	8	4	3
1	A	2	0	1
2	A	1	1	2
3	B	9	9	3
4	C	4	3	1
5	D	7	2	2

6 rows × 4 columns

Sort by multiple columns:

DT[:, :, dt.sort("col2", "col3")]

	col1	col2	col3	col4
	str32	int32	int32	int32
0	A	1	1	2
1	A	2	0	1
2	C	4	3	1
3	D	7	2	2
4	NA	8	4	3
5	B	9	9	3

6 rows × 4 columns

Sort in descending order:

DT[:, :, dt.sort(-f.col1)]

	col1	col2	col3	col4
	str32	int32	int32	int32
0	NA	8	4	3
1	D	7	2	2
2	C	4	3	1
3	B	9	9	3
4	A	2	0	1
5	A	1	1	2

6 rows × 4 columns

The frame can also be sorted in descending order by setting the reverse parameter to True:

DT[:, :, dt.sort("col1", reverse=True)]

	col1	col2	col3	col4
	str32	int32	int32	int32
0	NA	8	4	3
1	D	7	2	2
2	C	4	3	1
3	B	9	9	3
4	A	2	0	1
5	A	1	1	2

6 rows × 4 columns

By default, when sorting, null values are placed at the top; to relocate null values to the bottom, pass last to the na_position parameter:

DT[:, :, dt.sort("col1", na_position="last")]

	col1	col2	col3	col4
	str32	int32	int32	int32
0	A	2	0	1
1	A	1	1	2
2	B	9	9	3
3	C	4	3	1
4	D	7	2	2
5	NA	8	4	3

6 rows × 4 columns

Passing remove to na_position completely excludes any row with null values from the sorted output:

DT[:, :, dt.sort("col1", na_position="remove")]

	col1	col2	col3	col4
	str32	int32	int32	int32
0	A	2	0	1
1	A	1	1	2
2	B	9	9	3
3	C	4	3	1
4	D	7	2	2

5 rows × 4 columns

Sort by multiple columns, descending and ascending order:

DT[:, :, dt.sort(-f.col2, f.col3)]

	col1	col2	col3	col4
	str32	int32	int32	int32
0	B	9	9	3
1	NA	8	4	3
2	D	7	2	2
3	C	4	3	1
4	A	2	0	1
5	A	1	1	2

6 rows × 4 columns

The same code above can be replicated by passing a list of booleans to reverse. The length of the reverse flag list should match the number of columns to be sorted:

DT[:, :, dt.sort("col2", "col3", reverse=[True, False])]

	col1	col2	col3	col4
	str32	int32	int32	int32
0	B	9	9	3
1	NA	8	4	3
2	D	7	2	2
3	C	4	3	1
4	A	2	0	1
5	A	1	1	2

6 rows × 4 columns

In the presence of by(), sort() sorts within each group:

DT[:, :, by("col4"), dt.sort(f.col2)]

	col4	col1	col2	col3
	int32	str32	int32	int32
0	1	A	2	0
1	1	C	4	3
2	2	A	1	1
3	2	D	7	2
4	3	NA	8	4
5	3	B	9	9

6 rows × 4 columns