如何在numpy中将字符串值分配给数组?

问题描述

当我尝试将字符串分配给这样的数组时:

When I try to assign a string to an array like this:

CoverageACol[0,0] = "Hello"

我收到以下错误

Traceback (most recent call last):
  File "<pyshell#19>", line 1, in <module>
    CoverageACol[0,0] = "hello"
ValueError: setting an array element with a sequence.

但是，分配整数不会导致错误:

However, assigning an integer does not result in an error:

CoverageACol[0,0] = 42

CoverageACol是一个numpy数组.

CoverageACol is a numpy array.

请帮助！谢谢！

推荐答案

由于NumPy的数组为均一，表示它是所有相同类型元素的多维表.这与常规" Python中的多维列表列表不同，在多维列表中，列表中可以包含不同类型的对象.

You get the error because NumPy's array is homogeneous, meaning it is a multidimensional table of elements all of the same type. This is different from a multidimensional list-of-lists in "regular" Python, where you can have objects of different type in a list.

常规Python:

>>> CoverageACol = [[0, 1, 2, 3, 4],
                    [5, 6, 7, 8, 9]]

>>> CoverageACol[0][0] = "hello"

>>> CoverageACol
    [['hello', 1, 2, 3, 4],
     [5, 6, 7, 8, 9]]

NumPy:

>>> from numpy import *

>>> CoverageACol = arange(10).reshape(2,5)

>>> CoverageACol
    array([[0, 1, 2, 3, 4],
           [5, 6, 7, 8, 9]])

>>> CoverageACol[0,0] = "Hello"
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)

/home/biogeek/<ipython console> in <module>()

ValueError: setting an array element with a sequence.

因此，这取决于您要实现的目标，为什么要将字符串存储在用数字填充的其余数组中?如果这确实是您想要的，则可以将NumPy数组的数据类型设置为字符串:

So, it depends on what you want to achieve, why do you want to store a string in an array filled for the rest with numbers? If that really is what you want, you can set the datatype of the NumPy array to string:

>>> CoverageACol = array(range(10), dtype=str).reshape(2,5)

>>> CoverageACol
    array([['0', '1', '2', '3', '4'],
           ['5', '6', '7', '8', '9']],
           dtype='|S1')

>>> CoverageACol[0,0] = "Hello"

>>> CoverageACol
    array([['H', '1', '2', '3', '4'],
         ['5', '6', '7', '8', '9']],
         dtype='|S1')

请注意，仅分配了Hello的第一个字母.如果您希望分配整个单词，则需要设置数组-协议类型字符串:

Notice that only the first letter of Hello gets assigned. If you want the whole word to get assigned, you need to set an array-protocol type string:

>>> CoverageACol = array(range(10), dtype='a5').reshape(2,5)

>>> CoverageACol:
    array([['0', '1', '2', '3', '4'],
           ['5', '6', '7', '8', '9']],
           dtype='|S5')

>>> CoverageACol[0,0] = "Hello"

>>> CoverageACol
    array([['Hello', '1', '2', '3', '4'],
           ['5', '6', '7', '8', '9']],
           dtype='|S5')

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