x和y必须具有相同的第一维，但具有形状（30，）和（1，）

Question

我的Python版本：Python 3.6.1。

当我测试下面的程序，我得到一些错误。

可能是由于training_cost的维度为1x3，training_cost的维度可能导致错误。

""" 
multiple_eta 
~~~~~~~~~~~~~~~ 
This program shows how different values for the learning rate affect 
training. In particular, we'll plot out how the cost changes using 
three different values for eta. 
""" 

# Standard library 
import json 
import random 
import sys 
# My library 
sys.path.append('../') 
import mnist_loader 
import network2 
# Third-party libraries 
import matplotlib.pyplot as plt 
import numpy as np 

# Constants 
LEARNING_RATES = [0.025, 0.25, 2.5] 
COLORS = ['#2A6EA6', '#FFCD33', '#FF7033'] 
NUM_EPOCHS = 30 

def main(): 
    run_network() 
    make_plot() 

def run_network(): 
    """Train networks using three different values for the learning rate, 
    and store the cost curves in the file ``multiple_eta.json``, where 
    they can later be used by ``make_plot``. 
    """ 
    # Make results more easily reproducible 
    random.seed(12345678) 
    np.random.seed(12345678) 
    training_data, validation_data, test_data = mnist_loader.load_data_wrapper() 
    results = [] 
    for eta in LEARNING_RATES: 
     print ("\nTrain a network using eta = "+str(eta)) 
     net = network2.Network([784,30,10]) 
     results.append(net.SGD(training_data, NUM_EPOCHS, 10, eta, lmbda = 5.0, 
         evaluation_data=validation_data, monitor_training_cost=True)) 
    f = open("multiple_eta.json","w") 
    json.dump(results,f) 
    f.close() 

def make_plot(): 
    f = open("multiple_eta.json", "r") 
    results = json.load(f) 
    f.close() 
    fig = plt.figure() 
    ax = fig.add_subplot(111) 
    for eta, result, color in zip(LEARNING_RATES, results, COLORS): 
     _,_,training_cost,_ = result 
     print(training_cost) 
    ax.plot(np.arange(NUM_EPOCHS), training_cost, "o-",label = "$\eta$ = "+str(eta),color = color) 
    ax.set_xlim([0,NUM_EPOCHS]) 
    ax.set_xlabel('Epoch') 
    ax.set_ylabel('Cost') 
    plt.legend(loc = 'upper right') 
    plt.show() 

if __name__ == "__main__": 
    main() 

错误信息：

Train a network using eta = 0.025 
Epoch 0 training complete 
Cost on training data: 731.8195315067348 

Train a network using eta = 0.25 
Epoch 0 training complete 
Cost on training data: 2526.705883226454 

Train a network using eta = 2.5 
Epoch 0 training complete 
Cost on training data: 14014.828642157932 
[731.8195315067348] 
[2526.705883226454] 
[14014.828642157932] 
--------------------------------------------------------------------------- 
ValueError        Traceback (most recent call last) 
<ipython-input-11-b81c2d8fafc3> in <module>() 
    64 
    65 if __name__ == "__main__": 
---> 66  main() 

<ipython-input-11-b81c2d8fafc3> in main() 
    26 def main(): 
    27  run_network() 
---> 28  make_plot() 
    29 
    30 def run_network(): 

<ipython-input-11-b81c2d8fafc3> in make_plot() 
    56   _,_,training_cost,_ = result 
    57   print(training_cost) 
---> 58  ax.plot(np.arange(NUM_EPOCHS), training_cost, "o-",label = "$\eta$ = "+str(eta),color = color) 
    59  ax.set_xlim([0,NUM_EPOCHS]) 
    60  ax.set_xlabel('Epoch') 

c:\users\ray\appdata\local\programs\python\python36\lib\site-packages\matplotlib\__init__.py in inner(ax, *args, **kwargs) 
    1896      warnings.warn(msg % (label_namer, func.__name__), 
    1897         RuntimeWarning, stacklevel=2) 
-> 1898    return func(ax, *args, **kwargs) 
    1899   pre_doc = inner.__doc__ 
    1900   if pre_doc is None: 

c:\users\ray\appdata\local\programs\python\python36\lib\site-packages\matplotlib\axes\_axes.py in plot(self, *args, **kwargs) 
    1404   kwargs = cbook.normalize_kwargs(kwargs, _alias_map) 
    1405 
-> 1406   for line in self._get_lines(*args, **kwargs): 
    1407    self.add_line(line) 
    1408    lines.append(line) 

c:\users\ray\appdata\local\programs\python\python36\lib\site-packages\matplotlib\axes\_base.py in _grab_next_args(self, *args, **kwargs) 
    405     return 
    406    if len(remaining) <= 3: 
--> 407     for seg in self._plot_args(remaining, kwargs): 
    408      yield seg 
    409     return 

c:\users\ray\appdata\local\programs\python\python36\lib\site-packages\matplotlib\axes\_base.py in _plot_args(self, tup, kwargs) 
    383    x, y = index_of(tup[-1]) 
    384 
--> 385   x, y = self._xy_from_xy(x, y) 
    386 
    387   if self.command == 'plot': 

c:\users\ray\appdata\local\programs\python\python36\lib\site-packages\matplotlib\axes\_base.py in _xy_from_xy(self, x, y) 
    242   if x.shape[0] != y.shape[0]: 
    243    raise ValueError("x and y must have same first dimension, but " 
--> 244        "have shapes {} and {}".format(x.shape, y.shape)) 
    245   if x.ndim > 2 or y.ndim > 2: 
    246    raise ValueError("x and y can be no greater than 2-D, but have " 

ValueError: x and y must have same first dimension, but have shapes (30,) and (1,) 

原代码可以发现here。如何解决这个问题？

Answer 1

跟踪堆栈回到它看起来像这个问题是在

ax.plot(np.arange(NUM_EPOCHS), training_cost, ... 

NUM_EPOCHS大概是30，因为这是在错误信息的x的形状。 training_cost必须有形状（1，）。对于普通的x，y图，两个变量都应该具有相同的点数。

那么为什么training_cost只是一个项目？您的打印显示您设置一个循环中，并退出循环前的最后一个值是

[14014.828642157932] 

你为什么想要绘制一个价值？对30个点的轴？

results = json.load(f)给出了什么？