将带括号的字符串转换为numpy数组 [英] Convert a string with brackets to numpy array

问题描述

我在dataframe列中有一个像字符串一样的数组结构(我从csv文件中读取了dataframe).

I have an array-like structure in a dataframe column as a string (I read the dataframe from a csv file).

此列的一个字符串元素如下所示:

One string element of this column looks like this:

In  [1]: df.iloc[0]['points']    
Out [2]: '[(-0.0426, -0.7231, -0.4207), (0.2116, -0.1733, -0.1013), (...)]'

所以它实际上是一个类似数组的结构，对我来说看起来已经为numpy准备好了".

so it's really an array-like structure, which looks 'ready for numpy' to me.

numpy.fromstring()没有帮助，因为它不喜欢方括号:
在python中将数组的字符串表示转换为numpy数组

numpy.fromstring() doesn't help as it doesn't like brackets:
convert string representation of array to numpy array in python

如果我将其复制并粘贴到array()函数中，则字符串本身上的简单numpy.array()将返回一个numpy数组.
但是，如果我用包含如下字符串的变量填充array()函数:np.array(df.iloc[0]['points'])它不起作用，给我ValueError: could not convert string to float

A simple numpy.array() on the string itself, if I copy and paste it in the array() function is returning me a numpy array.
But if I fill the array() function with the variable containing the string like that: np.array(df.iloc[0]['points']) it does not work, giving me a ValueError: could not convert string to float

将字符串转换为numpy数组

是否有任何功能可以以简单的方式做到这一点(无需更换或重新放置括号)?

Is there any function to do that in a simple way (without replacing or regex-ing the brackets)?

推荐答案

在传递给numpy.array之前，可以使用ast.literal_eval:

You can use ast.literal_eval before passing to numpy.array:

from ast import literal_eval
import numpy as np

x = '[(-0.0426, -0.7231, -0.4207), (0.2116, -0.1733, -0.1013)]'

res = np.array(literal_eval(x))

print(res)

array([[-0.0426, -0.7231, -0.4207],
       [ 0.2116, -0.1733, -0.1013]])

您可以对Pandas系列中的字符串进行等效处理，但是尚不清楚是否需要跨行聚合.在这种情况下，您可以合并使用上述逻辑派生的NumPy数组的列表.

You can do the equivalent with strings in a Pandas series, but it's not clear if you need to aggregate across rows. If this is the case, you can combine a list of NumPy arrays derived using the above logic.

文档解释了 literal_eval 可接受的类型:

The docs explain types acceptable to literal_eval:

安全地评估表达式节点或包含Python的字符串 文字或容器显示.提供的字符串或节点只能 由以下Python文字结构组成:字符串，字节， 数字，元组，列表，字典，集合，布尔值和None.

Safely evaluate an expression node or a string containing a Python literal or container display. The string or node provided may only consist of the following Python literal structures: strings, bytes, numbers, tuples, lists, dicts, sets, booleans, and None.

因此，我们正在有效地将字符串转换为元组列表，然后np.array然后可以将其转换为NumPy数组.

So we are effectively converting a string to a list of tuples, which np.array can then convert to a NumPy array.

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