Python Numpy recarray.compress()函数

在numpy中，数组可以有一个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)] ，其中数组中的每个条目是一对(int, float)。通常情况下，这些属性使用字典查询，如arr[‘a’] 和arr[‘b’] 。

numpy.recarray.compress()函数允许将字段作为数组的成员访问，使用arr.a和arr.b。

语法: numpy.recarray.compress(condition, axis=None, out=None)

参数:
condition : [1-D array of bool] 选择要返回哪些条目的数组。
axis : [int, optional] 沿着哪个轴线进行切片。
out :结果将被放在这个数组中。

返回:compress_array, ndarray。

代码#1：

# Python program explaining
# numpy.recarray.compress() 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 int: ", rec_arr.b)
  
# applying recarray.compress methods to float record array
float_rec_arr = rec_arr.a
print("Record array of float: ", float_rec_arr)
out_arr = (rec_arr.a).compress([0, 1], axis = 0)
print ("Output compressed array : ", out_arr) 
  
# applying recarray.compress methods to int record array
int_rec_arr = rec_arr.b 
print("Record array of int: ", int_rec_arr)
out_arr = int_rec_arr.compress([True, False], axis = 1)
print ("Output compressed array : ", out_arr) 

输出:

Input array :  [[(5.0, 2) (3.0, -4) (6.0, 9)]
 [(9.0, 1) (5.0, 4) (-12.0, -7)]]
Record array of int:  [[ 2 -4  9]
 [ 1  4 -7]]
Record array of float:  [[  5.   3.   6.]
 [  9.   5. -12.]]
Output compressed array :  [[  9.   5. -12.]]
Record array of int:  [[ 2 -4  9]
 [ 1  4 -7]]
Output compressed array :  [[2]
 [1]]

代码#2：

# Python program explaining
# numpy.recarray.compress() 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 int: ", rec_arr.b)
  
# applying recarray.compress methods to whole record array
out_arr = rec_arr.compress([True, False], axis = 1)
print ("Output compressed array : ", out_arr) 

输出:

Input array :  [[(5.0, 2) (3.0, -4) (6.0, 9)]
 [(9.0, 1) (5.0, 4) (-12.0, -7)]]
Record array of int:  [[ 2 -4  9]
 [ 1  4 -7]]
Output compressed array :  [[(5.0, 2)]
 [(9.0, 1)]]