numpy.argsort¶

numpy.argsort(a,axis=-1,kind='quicksort',order=None)[source]¶

Returns the indices that would sort an array.

Perform an indirect sort along the given axis using the algorithm specifiedby thekind keyword. It returns an array of indices of the same shape asa that index data along the given axis in sorted order.

Parameters:

a : array_like Array to sort. axis : int or None, optional Axis along which to sort. The default is -1 (the last axis). If None,the flattened array is used. kind : {‘quicksort’, ‘mergesort’, ‘heapsort’}, optional Sorting algorithm. order : str or list of str, optional Whena is an array with fields defined, this argument specifieswhich fields to compare first, second, etc. A single field canbe specified as a string, and not all fields need be specified,but unspecified fields will still be used, in the order in whichthey come up in the dtype, to break ties.

Returns:

index_array : ndarray, int Array of indices that sorta along the specified axis.Ifa is one-dimensional,a[index_array] yields a sorteda.

See also

sort

Describes sorting algorithms used.

lexsort

Indirect stable sort with multiple keys.

ndarray.sort

Inplace sort.

argpartition

Indirect partial sort.

Notes

Seesort for notes on the different sorting algorithms.

As of NumPy 1.4.0argsort works with real/complex arrays containingnan values. The enhanced sort order is documented insort.

Examples

One dimensional array:

>>>x=np.array([3,1,2])>>>np.argsort(x)array([1, 2, 0])

Two-dimensional array:

>>>x=np.array([[0,3],[2,2]])>>>xarray([[0, 3],       [2, 2]])

>>>np.argsort(x,axis=0)array([[0, 1],       [1, 0]])

>>>np.argsort(x,axis=1)array([[0, 1],       [0, 1]])

Sorting with keys:

>>>x=np.array([(1,0),(0,1)],dtype=[('x','<i4'),('y','<i4')])>>>xarray([(1, 0), (0, 1)],      dtype=[('x', '<i4'), ('y', '<i4')])

>>>np.argsort(x,order=('x','y'))array([1, 0])

>>>np.argsort(x,order=('y','x'))array([0, 1])