子类化numpy ndarray问题

问题描述

我想继承numpy ndarray.但是，我不能更改数组.为什么self = ...不更改数组?谢谢.

I would like to subclass numpy ndarray. However, I cannot change the array. Why self = ... does not change the array? Thanks.

import numpy as np

class Data(np.ndarray):

    def __new__(cls, inputarr):
        obj = np.asarray(inputarr).view(cls)
        return obj

    def remove_some(self, t):
        test_cols, test_vals = zip(*t)
        test_cols = self[list(test_cols)]
        test_vals = np.array(test_vals, test_cols.dtype)

        self = self[test_cols != test_vals] # Is this part correct?

        print len(self) # correct result

z = np.array([(1,2,3), (4,5,6), (7,8,9)],
    dtype=[('a', int), ('b', int), ('c', int)])
d = Data(z)
d.remove_some([('a',4)])

print len(d)  # output the same size as original. Why?

推荐答案

也许使它成为函数而不是方法:

Perhaps make this a function, rather than a method:

import numpy as np

def remove_row(arr,col,val):
    return arr[arr[col]!=val]

z = np.array([(1,2,3), (4,5,6), (7,8,9)],
    dtype=[('a', int), ('b', int), ('c', int)])

z=remove_row(z,'a',4)
print(repr(z))

# array([(1, 2, 3), (7, 8, 9)],
#       dtype=[('a', '<i4'), ('b', '<i4'), ('c', '<i4')])

---

或者，如果您希望将其用作方法，

---

Or, if you want it as a method,

import numpy as np

class Data(np.ndarray):

    def __new__(cls, inputarr):
        obj = np.asarray(inputarr).view(cls)
        return obj

    def remove_some(self, col, val):
        return self[self[col] != val]

z = np.array([(1,2,3), (4,5,6), (7,8,9)],
    dtype=[('a', int), ('b', int), ('c', int)])
d = Data(z)
d = d.remove_some('a', 4)
print(d)

这里的主要区别是remove_some不会尝试修改self，它只会返回Data的新实例.

The key difference here is that remove_some does not try to modify self, it merely returns a new instance of Data.

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