Abstract

Sorts the array by the given axis, algorithm, and order. Note that there is a difference between the sort function and the sort method:

function

Returns a copy that is then sorted.

method

Returns None, and sorts the array in-place.

Function

Method

Property

Signature

Function: sort (arr, axis=-1, kind='quick', order=None)
Method: arr.sort (axis=-1, kind='quick', order=None)

Returns

Function: A sorted copy of arr.
Method: None. The sort is in-place and therefore affects the underlying array (no copy is made).

Arguments

arr

Array to be sorted.

axis

The axis the sort is applied to in a multi-dimensional array.

kind

The underlying algorithm to use. Also see: algorithms

'quick'
'heap'
'merge'

order

Used for arrays with fields defined. Can be one of the following:

A single string.
- Indicates that field as the basis for the sort.
A list or tuple of strings.
- Basis is in list order.
None
- If fields are defined, then the first field is the basis.

Details

algorithms

The various sorts are characterized by average speed, worst case performance, need for work space, and whether they are stable. A stable sort keeps items with the same key in the same relative order. The three available algorithms have the following properties:

kind	speed	worst case	work space	stable
quicksort	1	O(n^2)	0	no
mergesort	2	O(n*log(n))	~n/2	yes
heapsort	3	O(n*log(n))	0	no

All the sort algorithms make temporary copies of the data when the sort is not along the last axis. Consequently, sorts along the last axis are faster and use less space than sorts along other axis.

Example

sort()

In [1]: from numpy import *
In [2]: a = array([2,0,8,4,1])
In [3]: a.sort()         # in-place sorting with quicksort (default)
In [4]: a
Out[4]: array([0, 1, 2, 4, 8])

In [5]: a.sort(kind='mergesort') # algorithm options are 'quicksort', 'mergesort' and 'heapsort'
In [6]: a = array([[8,4,1],[2,0,9]])
In [7]: a.sort(axis=0)
In [8]: a
Out[8]:
array([[2, 0, 1],
       [8, 4, 9]])

In [9]: a = array([[8,4,1],[2,0,9]])
In [10]: a.sort(axis=1)      # default axis = -1
In [11]: a
Out[11]:
array([[1, 4, 8],
       [0, 2, 9]])

In [12]: sort(a)            # there is a functional form
Out[12]:
array([[1, 4, 8],
       [0, 2, 9]])

Notes

Docs in the source for the function are incorrect:

sort(a, axis=-1, kind='quicksort', order=None)
    Return copy of 'a' sorted along the given axis.

    Perform an inplace sort along the given axis using the algorithm
    specified by the kind keyword.

It should only say it returns a copy that is sorted. It does not have any side effect of sorting the underlying array in-place.

Function
Method
Property