将另一个numpy数组作为数组附加到numpy数组，而不是它的元素

Question

我想创建一个数组，但是当我使用np.append时，如果它们的元素：

import numpy as np
im_data = np.array(['image0','image1','image2','image3','image4','image5','image6','image7','image8','image9','image10','image11','image12','image13','image14'])
batches = [[1,2,3,4],[7,8,9,10],[3,4,5,6]]

image_batches = []
for batch in batches:
    image_batches = np.append(image_batches,[im_data[batch]])

这就是我得到的：

In: image_batches

Out: array(['image1', 'image2', 'image3', 'image4', 'image7', 'image8', 'image9', 'image10', 'image3', 'image4', 'image5', 'image6'], dtype='<U32')

这就是我需要的：

array([['image1', 'image2', 'image3', 'image4'], ['image7', 'image8', 'image9', 'image10'], ['image3', 'image4', 'image5', 'image6']], dtype='<U7')

我通过使用

image_batches = im_data[batches[0]]
for batch in batches[1:]:
    image_batches = np.vstack([image_batches, im_data[batch]])

但也许有更优雅的方式来做呢

Answer 1

正如@hpaulj在评论中提到的，您可以直接使用advances索引：

im_data[np.array(batches)]

输出：

[['image1' 'image2' 'image3' 'image4']
 ['image7' 'image8' 'image9' 'image10']
 ['image3' 'image4' 'image5' 'image6']]

Answer 2

您可以使用list comprehension，然后将其转换为numpy.array：

import numpy as np
im_data = np.array(['image0','image1','image2','image3','image4','image5','image6','image7','image8','image9','image10','image11','image12','image13','image14'])
batches = [[1,2,3,4],[7,8,9,10],[3,4,5,6]]

image_batches = np.array([im_data[batch_idx] for batch_idx in batches])
image_batches

输出：

array([['image1', 'image2', 'image3', 'image4'],
       ['image7', 'image8', 'image9', 'image10'],
       ['image3', 'image4', 'image5', 'image6']], dtype='<U7')

干杯