如何使用函数 numpy.append [英] How to use the function numpy.append

问题描述

我在使用函数 numpy.append 时遇到问题.我编写了以下函数作为较大代码段的一部分，但是，我的错误在以下内容中重现:

I have a problem using the function numpy.append. I wrote the following function as part of a larger piece of code, however, my error is reproduced in the folowing:

data = [
         [
          '3.5', '3', '0', '0', '15', '6', 
          '441', 'some text', 'some more complicated data'
         ], 
         [
          '4.5', '5', '1', '10', '165', '0', 
          '1', 'some other text', 'some even more complicated data'
         ]
       ]

def GetNumpyArrey(self, index):
    r = np.array([])
    for line in data:
        np.append(r, float(line[index]))

    print r

索引<6.结果是:

>> []

我做错了什么?

非常感谢！

推荐答案

与 list append 方法不同，numpy 的 append 不会就地追加.它返回一个附加了额外元素的新数组.所以你需要做 r = np.append(r, float(line[index])).

Unlike the list append method, numpy's append does not append in-place. It returns a new array with the extra elements appended. So you'd need to do r = np.append(r, float(line[index])).

不过，以这种方式构建 numpy 数组是低效的.最好将您的列表构建为 Python 列表，然后在最后创建一个 numpy 数组.

Building up numpy arrays in this way is inefficient, though. It's better to just build your list as a Python list and then make a numpy array at the end.

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