Numpy recarray.argsort() function | Python
Last Updated :
23 Apr, 2019
In numpy, arrays may have a data-types containing fields, analogous to columns in a spreadsheet. An example is
[(a, int), (b, float)], where each entry in the array is a pair of (int, float). Normally, these attributes are accessed using dictionary lookups such as
arr['a'] and arr['b'].
Record arrays allow the fields to be accessed as members of the array, using
arr.a and arr.b.
numpy.recarray.argsort() function returns the indices that would sort this array.
Syntax : numpy.recarray.argsort(arr, axis=-1, kind='quicksort', order=None)
Parameters:
arr : Input Record array.
axis : [int or None] Axis along which to sort. If None, the array is flattened before sorting. The default is -1, which sorts along the last axis.
kind : [‘quicksort’, ‘mergesort’, ‘heapsort’]Selection algorithm. Default is ‘quicksort’.
order : [str or list of str] When arr is an array with fields defined, this argument specifies which fields to compare first, second, etc.
Return : [index_array, ndarray] Array of indices that sort arr along the specified axis.
Code #1 :
Python3
# Python program explaining
# numpy.recarray.argsort() method
# importing numpy as geek
import numpy as geek
# creating input array with 2 different field
in_arr = geek.array([[(5.0, 2), (3.0, -4), (6.0, 9)],
[(9.0, 1), (5.0, 4), (-12.0, -7)]],
dtype =[('a', float), ('b', int)])
print ("Input array : ", in_arr)
# convert it to a record array,
# using arr.view(np.recarray)
rec_arr = in_arr.view(geek.recarray)
print("Record array of float: ", rec_arr.a)
print("Record array of int: ", rec_arr.b)
# applying recarray.argsort methods
# to float record array along axis 1
out_arr = geek.recarray.argsort(rec_arr.a, axis = 1)
print ("Output sorted array indices along axis 1: ", out_arr)
# applying recarray.argsort methods to
# int record array along axis 0
out_arr = geek.recarray.argsort(rec_arr.b, axis = 0)
print ("Output sorted array indices array along axis 0: ", out_arr)
Output:
Input array : [[(5.0, 2) (3.0, -4) (6.0, 9)]
[(9.0, 1) (5.0, 4) (-12.0, -7)]]
Record array of float: [[ 5. 3. 6.]
[ 9. 5. -12.]]
Record array of int: [[ 2 -4 9]
[ 1 4 -7]]
Output sorted array indices along axis 1: [[1 0 2]
[2 1 0]]
Output sorted array indices array along axis 0: [[1 0 1]
[0 1 0]]
Code #2 :
We are applying
numpy.recarray.argsort() to whole record array.
Python3
# Python program explaining
# numpy.recarray.argsort() method
# importing numpy as geek
import numpy as geek
# creating input array with 2 different field
in_arr = geek.array([[(5.0, 2), (3.0, 4), (6.0, -7)],
[(9.0, 1), (6.0, 4), (-2.0, -7)]],
dtype =[('a', float), ('b', int)])
print ("Input array : ", in_arr)
# convert it to a record array,
# using arr.view(np.recarray)
rec_arr = in_arr.view(geek.recarray)
# applying recarray.argsort methods to record array
out_arr = geek.recarray.argsort(rec_arr, kind ='heapsort')
print ("Output array : ", out_arr)
Output:
Input array : [[(5.0, 2) (3.0, 4) (6.0, -7)]
[(9.0, 1) (6.0, 4) (-2.0, -7)]]
Output sorted array indices : [[1 0 2]
[2 1 0]]
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