广播 4D numpy 数组

Question

I am facing an issue with broadcasting the processed 4D NumPy array into a 4D array. I have compared the dimensions to check something wrong with the dimensions. I am not understanding what's wrong.

train_path = files
train_file_names = os.listdir(train_path)
train_file_names.sort(key=lambda x: int(x.partition('.')[0]))
seg_num = 60
seg_len = 2
sample_num = len(df)
data = np.zeros((seg_num*100, 496, 64, 1))
label = np.zeros((seg_num * sample_num,))

for i, file_name in enumerate(train_file_names):
        sr, sound_file = wavfile.read(train_path + file_name)
        # print(train_path+file_name)
        length = sr * seg_len           # 5s segment
        range_high = len(sound_file) - length
        print(range_high, length)
        random_start = np.random.randint(range_high, size=seg_num)
        print("i", i)
        for j in range(seg_num):
            cur_wav = sound_file[random_start[j]:random_start[j] + length]
            cur_wav = cur_wav / 32768.0
            cur_spectro = preprocess_sound(cur_wav, sr)
            #print(cur_spectro.shape)
            cur_spectro = np.copy(np.expand_dims(cur_spectro, 3))
            print("cur_spectro",cur_spectro.shape)
            print("data", data.shape)
            print(data[i * seg_num + j, :, :, :].shape)
            data[i * seg_num + j, :, :, :] = cur_spectro
            label[i * seg_num + j] = df['class'][i]

Output

88200 88200
i 0
cur_spectro (0, 496, 64, 1)
data (6000, 496, 64, 1)
(496, 64, 1)
<ipython-input-226-30eefc542ce4> in loading_data(files, df)
      29                 print("data", data.shape)
      30                 print(data[i * seg_num + j, :, :, :].shape)
 ---> 31                 data[i * seg_num + j, :, :, :] = cur_spectro
      32                 label[i * seg_num + j] = df['class'][i]
      33 ValueError: could not broadcast input array from shape (0,496,64,1) into shape (496,64,1)

Answer 1

One of your printouts is cur_spectro (0, 496, 64, 1) .

See What does a numpy shape starting with zero mean It contains a description how to understand the case when one of array dimensions is zero . It means actually that the array in question is empty .

So it looks like you attempted to copy an empty array into a non-empty array. As in this situation these arrays can not be aligned (broadcast), the exception is raised.

Just as you can read in one of comments, analyze why preprocess_sound function returns as empty array.

Maybe you should add to your code a check whether the first dimension of cur_spectro has size zero and in such case you should either skip the offending instruction or copy to the target array some "surrogate" content.