如何将字符串值分配给numpy中的数组？

Question

当我尝试将字符串分配给这样的数组时：

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：

CoverageACol[0,0] = 42

CoverageACol 是一个 numpy 数组。

请帮忙！谢谢！

Answer 1

需要设置array的data type：

CoverageACol = numpy.array([["a","b"],["c","d"]],dtype=numpy.dtype('a16'))

这使得 ConerageACol 成为长度为 16 的字符串 (a) 数组。

Answer 2

您收到错误是因为 NumPy 的数组是 homogeneous, meaning it is a multidimensional table of elements all of the same type。这与“常规”Python 中的多维列表列表不同，您可以在列表中包含不同类型的对象。

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.

所以，这取决于你想要实现什么，你为什么要将一个字符串存储在一个数组中，其余部分用数字填充？如果这确实是您想要的，您可以将 NumPy 数组的数据类型设置为字符串：

>>> 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，只有Hello 的第一个字母被分配。如果要分配整个单词，则需要设置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')