Numpy MaskedArray.argmax()函数| Python

在许多情况下，数据集可能不完整或因存在无效数据而受到污染。例如，传感器可能无法记录数据，或记录无效值。 numpy.ma模块通过引入掩码数组提供了解决此问题的便捷方法。掩码数组是可能缺少或无效条目的数组。

numpy.MaskedArray.argmax()函数返回沿给定轴的最大值的索引数组。屏蔽值被视为具有值 fill_value..

Syntax : numpy.MaskedArray.argmax(axis=None, fill_value=None, out=None)

Parameters:
axis : [None, integer] If None, the index is into the flattened array, otherwise along the specified axis.
fill_value : [ var, optional] Value used to fill in the masked values.
out : [ndarray, optional] A location into which the result is stored.
  -> If provided, it must have a shape that the inputs broadcast to.
  -> If not provided or None, a freshly-allocated array is returned.

Return : [index_array ]A new integer_array is returned unless out is specified, in which case a reference to out is returned.

代码#1：

# Python program explaining
# numpy.MaskedArray.argmax() method 
  
# importing numpy as geek 
# and numpy.ma module as ma
import numpy as geek
import numpy.ma as ma
  
# creating input array 
in_arr = geek.array([1, 2, 3, -1, 5])
print ("Input array : ", in_arr)
  
# Now we are creating a masked array.
# by making third entry as invalid. 
mask_arr = ma.masked_array(in_arr, mask =[0, 0, 1, 0, 0])
print ("Masked array : ", mask_arr)
  
# applying MaskedArray.argmax methods to mask array
out_arr = mask_arr.argmax()
print ("Index of max element in masked array : ", out_arr)

输出：

Input array :  [ 1  2  3 -1  5]
Masked array :  [1 2 -- -1 5]
Index of max element in masked array :  4

代码#2：

# Python program explaining
# numpy.MaskedArray.argmax() method 
  
# importing numpy as geek 
# and numpy.ma module as ma
import numpy as geek
import numpy.ma as ma
  
# creating input array 
in_arr = geek.array([10, 20, 30, -10, 50])
print ("Input array : ", in_arr)
  
# Now we are creating a masked array
# by making first third entry as invalid. 
mask_arr = ma.masked_array(in_arr, mask =[1, 0, 1, 0, 0])
print ("Masked array : ", mask_arr)
  
# applying MaskedArray.argmax methods to mask array
# and filling the masked location by 100
out_arr = mask_arr.argmax(fill_value = 100)
print ("Index of max element in masked array : ", out_arr)

输出：

Input array :  [ 10  20  30 -10  50]
Masked array :  [-- 20 -- -10 50]
Index of max element in masked array :  0