Numpy recarray.argpartition()函数| Python
原文:https://www . geeksforgeeks . org/numpy-recarray-arg partition-function-python/
在 numpy 中，数组可能具有包含字段的数据类型，类似于电子表格中的列。一个例子是[(a, int), (b, float)]，数组中的每个条目都是一对(int，float)。通常，这些属性是使用字典查找来访问的，例如arr['a'] and arr['b']。
记录数组允许使用arr.a and arr.b作为数组成员访问字段。 numpy.recarray.argpartition() 函数返回分割该数组的索引。
语法:
numpy.recarray.argpartition(kth, axis=-1, kind='introselect', order=None)参数: kth:【int 或 ints 序列】要分区的元素索引。 轴:【int 或 None】要排序的轴。如果为“无”，则数组在排序前被展平。默认值为-1，沿最后一个轴排序。 种类:选择算法。默认值为“introselect”。 顺序:【字符串或字符串列表】当 arr 是定义了字段的数组时，此参数指定首先比较哪些字段，其次比较哪些字段等。
返回:【index _ Array，ndarray】沿指定轴划分数组的索引数组。
代码#1 :
# Python program explaining
# numpy.recarray.argpartition() 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.argpartition methods
# to float record array along axis 1
out_arr = geek.recarray.argpartition(rec_arr.a, kth = 1, axis = 1)
print ("Output partitioned array indices along axis 1: ", out_arr)
# applying recarray.argpartition methods
# to int record array along axis 0
out_arr = geek.recarray.argpartition(rec_arr.b, kth = 1, axis = 0)
print ("Output partitioned 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 partitioned array indices along axis 1: [[1 0 2]
[2 1 0]]
Output partitioned array indices array along axis 0: [[1 0 1]
[0 1 0]]
代码#2 :
我们将numpy.recarray.argpartition()应用于整个记录数组。
# Python program explaining
# numpy.recarray.argpartition() 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.argpartition methods to record array
out_arr = geek.recarray.argpartition(rec_arr, kth = 2)
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 array : [[1 0 2]
[2 1 0]]
