TensorFlow feed_dict 没有学习

Question

从 tensorflow 的 MNIST tutorial 复制和粘贴代码效果很好，准确度达到了 92%，正如预期的那样。

当我以 CSV 格式读取 MNIST 数据并使用 pd.DataFrame.values 转换为 np 数组时，此过程会中断。我从中得到了~10%（不比随机更好）的准确度。

下面是代码（教程代码运行良好，我的CSV阅读器学习失败）：

工作 MNIST 教程：

from tensorflow.examples.tutorials.mnist import input_data
mnist = input_data.read_data_sets("MNIST_data/", one_hot=True)


x = tf.placeholder(tf.float32, [None, 784])
W = tf.Variable(tf.zeros([784, 10]))
b = tf.Variable(tf.zeros([10]))
y = tf.nn.softmax(tf.matmul(x, W) + b)
y_ = tf.placeholder(tf.float32, [None, 10])
cross_entropy = tf.reduce_mean(-tf.reduce_sum(y_ * tf.log(y), reduction_indices=[1]))
train_step = tf.train.GradientDescentOptimizer(0.5).minimize(cross_entropy)
init = tf.initialize_all_variables()
sess = tf.Session()
sess.run(init)

for i in range(1000):
  batch_xs, batch_ys = mnist.train.next_batch(100)
  sess.run(train_step, feed_dict={x: batch_xs, y_: batch_ys})


correct_prediction = tf.equal(tf.argmax(y,1), tf.argmax(y_,1))
accuracy = tf.reduce_mean(tf.cast(correct_prediction, tf.float32))
print(sess.run(accuracy, feed_dict={x: mnist.test.images, y_: mnist.test.labels}))

不工作（读取 CSV 并提供 np 数组）：

import pandas as pd
from sklearn.cross_validation import train_test_split
import numpy as np    

# read csv file
MNIST = pd.read_csv("/data.csv")

# pop label column and create training label array
train_label = MNIST.pop("label")

# converts from dataframe to np array
MNIST=MNIST.values

# convert train labels to one hots
train_labels = pd.get_dummies(train_label)
# make np array
train_labels = train_labels.values

x_train,x_test,y_train,y_test = train_test_split(MNIST,train_labels,test_size=0.2)
# we now have features (x_train) and y values, separated into test and train

# convert to dtype float 32
x_train,x_test,y_train,y_test = np.array(x_train,dtype='float32'), np.array(x_test,dtype='float32'),np.array(y_train,dtype='float32'),np.array(y_test,dtype='float32')



x = tf.placeholder(tf.float32, [None, 784])
W = tf.Variable(tf.zeros([784, 10]))
b = tf.Variable(tf.zeros([10]))
y = tf.nn.softmax(tf.matmul(x, W) + b)
y_ = tf.placeholder(tf.float32, [None, 10])
cross_entropy = tf.reduce_mean(-tf.reduce_sum(y_ * tf.log(y), reduction_indices=[1]))
train_step = tf.train.GradientDescentOptimizer(0.5).minimize(cross_entropy)
init = tf.initialize_all_variables()
sess = tf.Session()
sess.run(init)

def get_mini_batch(x,y):
    # choose 100 random row values
    rows=np.random.choice(x.shape[0], 100)
    # return arrays of 100 random rows (for features and labels)
    return x[rows], y[rows]

# train
for i in range(100):
    # get mini batch
    a,b=get_mini_batch(x_train,y_train)
    # run train step, feeding arrays of 100 rows each time
    sess.run(train_step, feed_dict={x: a, y_: b})

correct_prediction = tf.equal(tf.argmax(y,1), tf.argmax(y_,1))
accuracy = tf.reduce_mean(tf.cast(correct_prediction, tf.float32))
print(sess.run(accuracy, feed_dict={x: x_test, y_: y_test}))

我们将不胜感激。 （CSV 文件here。）

Answer 1

您是否尝试训练它进行更多迭代？我看到原始代码正在训练超过 1000 次迭代

for i in range(1000):

而 csv 代码只训练 100 次迭代：

for i in range(100):

如果不是这个原因，如果您也可以共享您的 CSV 文件，那将会很有帮助，因为我们可以轻松地测试您的代码。

编辑：

我已经测试了您的代码，它似乎是由简单的cross_entropy 计算中的数值不稳定性引起的（请参阅此SO question）。将您的 cross_entropy 定义替换为以下行，您就可以解决问题：

cross_entropy = tf.reduce_mean(tf.reduce_sum(tf.nn.softmax_cross_entropy_with_logits(
    y, y_, name='xentropy')))

通过还可视化返回的 cross_entropy，您将看到您的代码返回 NaN，而使用此代码您将获得实数...

完整的工作代码，每次迭代也会打印出 cross_entropy：

import pandas as pd
from sklearn.cross_validation import train_test_split
import numpy as np    

# read csv file
MNIST = pd.read_csv("data.csv")

# pop label column and create training label array
train_label = MNIST.pop("label")

# converts from dataframe to np array
MNIST=MNIST.values

# convert train labels to one hots
train_labels = pd.get_dummies(train_label)
# make np array
train_labels = train_labels.values

x_train,x_test,y_train,y_test = train_test_split(MNIST,train_labels,test_size=0.2)
# we now have features (x_train) and y values, separated into test and train

# convert to dtype float 32
x_train,x_test,y_train,y_test = np.array(x_train,dtype='float32'), np.array(x_test,dtype='float32'),np.array(y_train,dtype='float32'),np.array(y_test,dtype='float32')

x = tf.placeholder(tf.float32, [None, 784])
W = tf.Variable(tf.zeros([784, 10]))
b = tf.Variable(tf.zeros([10]))
y = tf.nn.softmax(tf.matmul(x, W) + b)
y_ = tf.placeholder(tf.float32, [None, 10])
print y.get_shape()
print y_.get_shape()
cross_entropy = tf.reduce_mean(tf.reduce_sum(tf.nn.softmax_cross_entropy_with_logits(y, y_, name='xentropy')))
train_step = tf.train.GradientDescentOptimizer(0.0001).minimize(cross_entropy)
init = tf.initialize_all_variables()
sess = tf.Session()
sess.run(init)

def get_mini_batch(x,y):
    # choose 100 random row values
    rows=np.random.choice(x.shape[0], 100)
    # return arrays of 100 random rows (for features and labels)
    return x[rows], y[rows]

# train
for i in range(1000):
    # get mini batch
    a,b=get_mini_batch(x_train,y_train)
    # run train step, feeding arrays of 100 rows each time
    _, cost =sess.run([train_step,cross_entropy], feed_dict={x: a, y_: b})
    print cost

correct_prediction = tf.equal(tf.argmax(y,1), tf.argmax(y_,1))
accuracy = tf.reduce_mean(tf.cast(correct_prediction, tf.float32))
print(sess.run(accuracy, feed_dict={x: x_test, y_: y_test}))

您仍然需要进一步优化学习率和#iterations，但使用此设置您应该已经获得了约 70% 的准确度。

Answer 2

我很确定批次不应该是 100 个随机行，而是应该是 100 个彼此接连出现的行，例如，0:99 和 100:199 将是您的前两个批次。试试这个代码的批次。检查此kernel 以在 TF 中从 csv 训练 Mnist

epochs_completed = 0
index_in_epoch = 0
num_examples = train_images.shape[0]

# serve data by batches
def next_batch(batch_size):

    global train_images
    global train_labels
    global index_in_epoch
    global epochs_completed

    start = index_in_epoch
    index_in_epoch += batch_size

    # when all trainig data have been already used, it is reorder randomly    
    if index_in_epoch > num_examples:
        # finished epoch
        epochs_completed += 1
        # shuffle the data
        perm = np.arange(num_examples)
        np.random.shuffle(perm)
        train_images = train_images[perm]
        train_labels = train_labels[perm]
        # start next epoch
        start = 0
        index_in_epoch = batch_size
        assert batch_size <= num_examples
    end = index_in_epoch
    return train_images[start:end], train_labels[start:end]