python - numpy - 如何为数组第一列中的每个元素添加一个值？

Question

我有一个这样的数组:

array([('6506', 4.6725971801473496e-25, 0.99999999995088695),
       ('6601', 2.2452745388799898e-27, 0.99999999995270605),
       ('21801', 1.9849650921836601e-31, 0.99999999997999001), ...,
       ('45164194', 1.0413482803123399e-24, 0.99999999997453404),
       ('45164198', 1.09470356446595e-24, 0.99999999997635303),
       ('45164519', 3.7521365799080699e-24, 0.99999999997453404)], 
      dtype=[('pos', '|S100'), ('par1', '<f8'), ('par2', '<f8')])

我想把它变成这样:(在第一列的每个值上添加前缀“2R”)

array([('2R:6506', 4.6725971801473496e-25, 0.99999999995088695),
       ('2R:6601', 2.2452745388799898e-27, 0.99999999995270605),
       ('2R:21801', 1.9849650921836601e-31, 0.99999999997999001), ...,
       ('2R:45164194', 1.0413482803123399e-24, 0.99999999997453404),
       ('2R:45164198', 1.09470356446595e-24, 0.99999999997635303),
       ('2R:45164519', 3.7521365799080699e-24, 0.99999999997453404)], 
      dtype=[('pos', '|S100'), ('par1', '<f8'), ('par2', '<f8')])

我查了一些关于 nditer 的资料(但我想支持早期版本的 numpy。)我也在读一本应该避免迭代的书。

Answer 1

使用 numpy.core.defchararray.add :

>>> from numpy import array
>>> from numpy.core.defchararray import add
>>>
>>> xs = array([('6506', 4.6725971801473496e-25, 0.99999999995088695),
...             ('6601', 2.2452745388799898e-27, 0.99999999995270605),
...             ('21801', 1.9849650921836601e-31, 0.99999999997999001),
...             ('45164194', 1.0413482803123399e-24, 0.99999999997453404),
...             ('45164198', 1.09470356446595e-24, 0.99999999997635303),
...             ('45164519', 3.7521365799080699e-24, 0.99999999997453404)],
...            dtype=[('pos', '|S100'), ('par1', '<f8'), ('par2', '<f8')])
>>> xs['pos'] = add('2R:', xs['pos'])
>>> xs
array([('2R:6506', 4.67259718014735e-25, 0.999999999950887),
       ('2R:6601', 2.24527453887999e-27, 0.999999999952706),
       ('2R:21801', 1.98496509218366e-31, 0.99999999997999),
       ('2R:45164194', 1.04134828031234e-24, 0.999999999974534),
       ('2R:45164198', 1.09470356446595e-24, 0.999999999976353),
       ('2R:45164519', 3.75213657990807e-24, 0.999999999974534)],
      dtype=[('pos', 'S100'), ('par1', '<f8'), ('par2', '<f8')])

更新:您可以使用 num.char.add而不是 numpy.core.defchararray.add(@joel-buursma 评论):

>>> import numpy
>>> numpy.char == numpy.core.defchararray
True