如何在numpy中为字符串赋值？

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

你得到错误是因为NumPy的数组是同构的,这意味着它是一个多维表格的所有相同类型的元素.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的:

>>> 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.

那么,这取决于你想要实现的目标,为什么你要将一个字符串存储在一个数组中？如果这真的是你想要的,你可以将NumPy数组的数据类型设置为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,只Hello分配了第一个字母.如果要分配整个单词,则需要设置数组协议类型字符串:

>>> 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')

Answer 2

您需要设置的数据类型的的数组:

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.