Tensorflow基础API

Tensorflow基础API

1.@tf.function

• 它可以将python函数编译成图结构。

• 易于将模型导出成为GraphDef+checkpoint 或者SavedModel使得eager execution可以默认打开

• 它还可以将Tensorflow1.0代码通过tf.function进行封装再Tensorflow2.0里使用

2.tf.constant([])

• 常量

  t = tf.constant([[1.,2.,3.],[4.,5.,6.]])
  print(t)
  print(t[:,1:])
  print(t[...,1])
  """
  tf.Tensor(
  [[1. 2. 3.]
   [4. 5. 6.]], shape=(2, 3), dtype=float32)
  tf.Tensor(
  [[2. 3.]
   [5. 6.]], shape=(2, 2), dtype=float32)
  tf.Tensor([2. 5.], shape=(2,), dtype=float32)
  """
  

• 算子运算

  # 相加
  print(t+10)
  # 平方
  print(tf.square(t))
  # 转置
  print(t @ tf.transpose(t))
  

• tf 转numpy

  t.numpy()
  或
  np.square(t)
  

• numpy转tf

  np_t = np.array([[1.,2.,3.],[4.,5.,6.]])
  print(tf.constant(np_t))
  

• 零维tf转numpy

  t = tf.constant(2.766)
  print(t.numpy())
  print(t.shape)# () 代表零维
  """
  2.766
  ()
  """
  

3.tf.strings 与ragged_tensor

• tf.strings

  t = tf.constant("tom")
  # 
  print(t)
  # 打印长度
  print(tf.strings.length(t))
  # 长度
  print(tf.strings.length(t,unit="UTF8_CHAR"))
  # utf8 的 编码
  print(tf.strings.unicode_decode(t,"UTF8"))
  

• 也可以保存数组

  t = tf.constant(["cafe","coffee","咖啡"])
  print(tf.strings.length(t,unit="UTF8_CHAR"))
  r = tf.strings.unicode_decode(t,"UTF8")
  print(r)# 将数组中每一个字符串编码打印
  """
  tf.Tensor([4 6 2], shape=(3,), dtype=int32)
  <tf.RaggedTensor [[99, 97, 102, 101], [99, 111, 102, 102, 101, 101], [21654, 21857]]>
  """
  

• ragged tensor

  • 解决分布不固定的tensor,长度不固定，有长有短。

  r = tf.ragged.constant([[11,12],[21,22,23],[],[41]])
  print(r)
  print(r[1])
  print(r[1:3])
  """
  <tf.RaggedTensor [[11, 12], [21, 22, 23], [], [41]]>
  tf.Tensor([21 22 23], shape=(3,), dtype=int32)
  <tf.RaggedTensor [[21, 22, 23], []]>
  """
  

  • 合并

  r2 = tf.ragged.constant([[51,52],[],[7]])
  print(tf.concat([r,r2],axis=0))
  # <tf.RaggedTensor [[11, 12], [21, 22, 23], [], [41], [51, 52], [], [7]]>
  

  • 将ragged tensor 转换成tensor

  print(r.to_tensor())
  # 把没有的值用0补齐,补齐方式放在正常值后面
  """
  tf.Tensor(
  [[11 12  0]
   [21 22 23]
   [ 0  0  0]
   [41  0  0]], shape=(4, 3), dtype=int32)
  """
  

4.spars_tensor与tf.Variable

• spars_tensor

  # indices 所有正常值位置
  # values 上述正常值位置对应的值
  # dense_shape 矩阵具体大小
  # 注意SparseTensor必须排序好的，否则调用to_dense会报错
  s = tf.SparseTensor(indices=[[0,1],[1,0],[2,3]],values=[1.,2.,3.],dense_shape=[3,4])
  print(s)
  # 密集型矩阵
  print(tf.sparse.to_dense(s))
  """
  SparseTensor(indices=tf.Tensor(
  [[0 1]
   [1 0]
   [2 3]], shape=(3, 2), dtype=int64), values=tf.Tensor([1. 2. 3.], shape=(3,), dtype=float32), dense_shape=tf.Tensor([3 4], shape=(2,), dtype=int64))
  tf.Tensor(
  [[0. 1. 0. 0.]
   [2. 0. 0. 0.]
   [0. 0. 0. 3.]], shape=(3, 4), dtype=float32)
  """
  # 如果不是排好序的，可以先调用reorder再to_dense.
  s4 = tf.SparseTensor(indices=[[0,2],[0,1],[2,3]],values=[1.,2.,3.],dense_shape=[3,4])
  s5 = tf.sparse.reorder(s4)
  print(tf.sparse.to_dense(s5))
  

• sparse运算

  s2 = s * 2.0
  
  # 密集矩阵与sparse矩阵相乘
  s4 = tf.constant([
  	[10.,20.],
  	[30.,40.],
  	[50.,60.],
  	[70.,80.]
  ])
  # 3*4矩阵 乘以 4*2 得到3*2矩阵
  print(tf.sparse.sparse_dense_matmul(s,s4))
  """
  tf.Tensor(
  [[ 30.  40.]
   [ 20.  40.]
   [210. 240.]], shape=(3, 2), dtype=float32)
  """
  

• Variables 变量

  • 变量创建

  v = tf.Variable([[1.,2.,3.],[4.,5.,6.]])
  """
  <tf.Variable 'Variable:0' shape=(2, 3) dtype=float32, numpy=
  array([[1., 2., 3.],
         [4., 5., 6.]], dtype=float32)>
  """
  v.numpy()
  """
  array([[1., 2., 3.],
         [4., 5., 6.]], dtype=float32)
  """
  v.value()
  """
  <tf.Tensor: shape=(2, 3), dtype=float32, numpy=
  array([[1., 2., 3.],
         [4., 5., 6.]], dtype=float32)>
  """
  

  • 变量可以被重新赋值,使用assign函数

  # 对变量赋值
  v.assign(2*v)
  # 对某一位置重新赋值
  v.assign(2*v)
  # 对某一行重新赋值
  v[1].assign([7.,8.,9.])
  

5.自定义损失函数 + 自定义损失层次

• custonmized_mse为自定义损失函数。

def custonmized_mse(y_true,y_pred):
    # 求差值平方后的均值
    return tf.redece_mean(tf.square(y_pred-y_true))
model= keras.models.Sequential([
    keras.layers.Dense(30,activation='relu',input_shape=x_train.shape[1:]),
    keras.layers.Dense(1)
])
model.summary()
model.compile(loss=custonmized_mse,optimizer="sgd",metrics=["mean_squared_error"])
callbacks = [keras.callbacks.EarlyStopping(patience=5,min_delta=1e-2)]
history = model.fit(x_train_scaled,y_train,validation_data=(x_valid_scaled,y_valid),epochs=100,callbacks=callbacks)

• 自定义层次
  • DenseLayer做的事情是： x*w+b

layer.variables #打印所有参数
layer = tf.keras.layers.Dense(100, input_shape=(None,5))
layer(tf.zeros([10,5]))# 10*100矩阵

6.使子类与lambda分别实战自定义层

• 使用子类自定义层次

# 常规导报
import matplotlib as mpl
import matplotlib.pyplot as plt
%matplotlib inline
import numpy as np
import sklearn
import pandas as pd
import os
import sys
import time
import tensorflow as tf
from tensorflow import keras
# 打印版本
print(tf.__version__)
print(sys.version_info)
for module in mpl,np,pd,sklearn,tf,keras:
    print(module.__name__, module.__version__)
# 导入fetch_california_housing类
from sklearn.datasets import fetch_california_housing 
# 实例化对象
housing = fetch_california_housing()
# 打印相关信息
print(housing.DESCR)
print(housing.data.shape)
# 输出：(20640, 8)
print(housing.target.shape)


from sklearn.model_selection import train_test_split
#拆分训练集，测试集
x_train_all,x_test,y_train_all,y_test = train_test_split(
             housing.data , housing.target , random_state=7,test_size = 0.2)
# 拆分训练集，验证集
x_train,x_valid,y_train,y_valid = train_test_split(
                x_train_all , y_train_all , random_state=11)
print(x_train.shape, y_train.shape)
print(x_valid.shape, y_valid.shape)
print(x_test.shape, y_test.shape)



#导入StandardScaler类
from sklearn.preprocessing import StandardScaler
# 实例化
scaler = StandardScaler()
# 调用scaler。fit 或者scaler.transform方法
x_train_scaled = scaler.fit_transform(x_train)
x_valid_scaled = scaler.transform(x_valid)
x_test_scaled = scaler.transform(x_test)

• 子类自定义层 CustomizedDenseLayer

  class CustomizedDenseLayer(keras.layers.Layer):
      def __init__(self, units, activation=None,**kwargs):
          self.units = units# 输出单元数
          self.activation = keras.layers.Activation(activation)# 要用到激活函数
          # 调用父类函数
          super(CustomizedDenseLayer, self).__init__(**kwargs)
      def build(self, input_shape):
          """构建需要的参数"""
          # x * w + b  # input_shape:[None, a] w: [a,b]    output_shape: [None, b]
          # 
          self.kernel = self.add_weight(name='kernel', shape=(input_shape[1], self.units),initializer='uniform',trainable=True)
          self.bias = self.add_weight(name='bias', shape=(self.units,), initializer='zeros', trainable=True)
          super(CustomizedDenseLayer, self).build(input_shape)
          
      def call(self, x):
          """完成正向计算"""
          return self.activation(x @ self.kernel + self.bias)
  
      
  model= keras.models.Sequential([
      CustomizedDenseLayer(30,activation='relu',input_shape=x_train.shape[1:]),
      CustomizedDenseLayer(1)
  ])
  
  model.summary()
  model.compile(loss="mean_squared_error",optimizer="sgd")
  callbacks = [keras.callbacks.EarlyStopping(patience=5,min_delta=1e-2)]
  history = model.fit(x_train_scaled,y_train,validation_data=(x_valid_scaled,y_valid),epochs=100,callbacks=callbacks)
  
  

• lambda方式自定义层次

  customized_softplus = keras.layers.Lambda(lambda x: tf.nn.softplus(x))
  # 上面表示带softplus激活函数的Dense层，它等价于：
  	1.keras.layers.Dense(1, activation="softplus")
  	2. keras.layers.Dense(1), keras.layers.Activation('softplus')
  # 示例：
  model= keras.models.Sequential([
      CustomizedDenseLayer(30,activation='relu',input_shape=x_train.shape[1:]),
      CustomizedDenseLayer(1),
      customized_softplus
  ])
  

7.tf.function函数转换

• tf.function可以将python式的函数转换成tensorflow 能运行的函数， 转换后运行的速度会得到提高，特别GPU加速的tensorflow运行的比一般python函数更快。

• 定义一个python函数

  # tf.function and auto-graph
  
  def scaled_elu(z, scale=1.0, alpha=1.0):
      # z>=0 ? scale * z :scale *alpha * tf.nn.elu(z)
      is_positive = tf.greater_equal(z, 0.0)
      return scale * tf.where(is_positive, z , alpha * tf.nn.elu(z))
  

• 输入标量和输入向量

  # 输入标量
  print(scaled_elu(tf.constant(-3.)))
  # 输入向量
  print(scaled_elu(tf.constant([-3.,-2.5])))
  """
  tf.Tensor(-0.95021296, shape=(), dtype=float32)
  tf.Tensor([-0.95021296 -0.917915  ], shape=(2,), dtype=float32)
  """
  

• 把python语法实现的函数，用tf.function变成tensorflow图实现的函数。并输入标量和向量

  scaled_elu_tf = tf.function(scaled_elu)
  # 输入标量
  print(scaled_elu_tf(tf.constant(-3.)))
  # 输入向量
  print(scaled_elu_tf(tf.constant([-3.,-2.5])))
  """
  tf.Tensor(-0.95021296, shape=(), dtype=float32)
  tf.Tensor([-0.95021296 -0.917915  ], shape=(2,), dtype=float32)
  """
  

  可见上面，输出结果是一样的

• 获取tf.function获取python函数

  # 获取python的函数
  print(scaled_elu_tf.python_function is scaled_elu)# True
  

• 对比时间

  %timeit scaled_elu(tf.random.normal((1000,1000)))
  %timeit scaled_elu_tf(tf.random.normal((1000,1000)))
  """
  44.9 ms ± 7.17 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)
  44.6 ms ± 8.2 ms per loop (mean ± std. dev. of 7 runs, 10 loops each)
  """
  

• @tf.function装饰器转tf.function,如下示例：

  # 1 + 1/2 + 1/2^2 + ... 1/2^n
  
  @tf.function
  def converge_to_2(n_iters):
      total = tf.constant(0.)
      increment = tf.constant(1.)
      for _ in range(n_iters):
          total += increment
          increment /= 2.0
      return total
  print(converge_to_2(20))
  

• markdown方式现实tf.function的函数

  def display_tf_code(func):
      code = tf.autograph.to_code(func)
      from IPython.display import display, Markdown
      display(Markdown("```python\n{}\n```".format(code)))
      
  display_tf_code(scaled_elu)
  display_tf_code(converge_to_2)
  

  tf.Variable()不能定义再tf.function里面，否则报错：ValueError: tf.function-decorated function tried to create variables on non-first call.，应该定义再函数外面做初始化。

• @tf.function输入int类型和float类型 得到值：

  @tf.function
  def cube(z):
      return tf.pow(z,3)
  print(cube(tf.constant([1.,2.,3.])))
  print(cube(tf.constant([1,2,3])))
  """
  tf.Tensor([ 1.  8. 27.], shape=(3,), dtype=float32)
  tf.Tensor([ 1  8 27], shape=(3,), dtype=int32)
  """
  

8.函数签名与图结构

• tf.function 函数签名

  @tf.function(input_signature=[tf.TensorSpec([None], tf.int32, name='x')])
  def cube(z):
      return tf.pow(z,3)
  

  上述代表意思是输入z内元素的类型只能是int32

• 使用get_concrete_function加上input signature成为SaveModel

  # 要把类型传入进去
  cube_func_int32 = cube.get_concrete_function(tf.TensorSpec([None,],tf.int32))
  # <tensorflow.python.eager.function.ConcreteFunction object at 0x7f8d65a86d10>
  
  print(cube_func_int32 is cube.get_concrete_function(tf.TensorSpec([5], tf.int32)))
  # True
  
  print(cube_func_int32 is cube.get_concrete_function(tf.constant([1,2,3])))
  # True
  

• 通过 .graph获取图定义tf

  cube_func_int32.graph
  # 
  <tensorflow.python.framework.func_graph.FuncGraph at 0x7f8d692fbd10>
  

• 通过get_operations获取tf的操作

  cube_func_int32.graph.get_operations()
  """
  [<tf.Operation 'x' type=Placeholder>,
   <tf.Operation 'Pow/y' type=Const>,
   <tf.Operation 'Pow' type=Pow>,
   <tf.Operation 'Identity' type=Identity>]
  """
  

• 获取其中一个tf操作

  pow_op = cube_func_int32.graph.get_operations()[2]
  print(pow_op)
  """
  name: "Pow"
  op: "Pow"
  input: "x"
  input: "Pow/y"
  attr {
    key: "T"
    value {
      type: DT_INT32
    }
  }
  """
  
  # 获取输入】
  print(list(pow_op.inputs))
  # [<tf.Tensor 'x:0' shape=(None,) dtype=int32>, <tf.Tensor 'Pow/y:0' shape=() dtype=int32>]
  
  # 获取输出
  print(list(pow_op.outputs))
  # [<tf.Tensor 'Pow:0' shape=(None,) dtype=int32>]
  

• 获取tf完整图结构

  cube_func_int32.graph.as_graph_def()
  """
  node {
    name: "x"
    op: "Placeholder"
    attr {
      key: "_user_specified_name"
      value {
        s: "x"
      }
    }
    attr {
      key: "dtype"
      value {
        type: DT_INT32
      }
    }
    attr {
      key: "shape"
      value {
        shape {
          dim {
            size: -1
          }
        }
      }
    }
  }
  node {
    name: "Pow/y"
    op: "Const"
    attr {
      key: "dtype"
      value {
        type: DT_INT32
      }
    }
    attr {
      key: "value"
      value {
        tensor {
          dtype: DT_INT32
          tensor_shape {
          }
          int_val: 3
        }
      }
    }
  }
  node {
    name: "Pow"
    op: "Pow"
    input: "x"
    input: "Pow/y"
    attr {
      key: "T"
      value {
        type: DT_INT32
      }
    }
  }
  node {
    name: "Identity"
    op: "Identity"
    input: "Pow"
    attr {
      key: "T"
      value {
        type: DT_INT32
      }
    }
  }
  versions {
    producer: 175
  }
  """
  # 根据name获取tf.Operation 
  cube_func_int32.graph.get_operation_by_name("x")
  
  # 根据name获取tf.Tensor
  cube_func_int32.graph.get_tensor_by_name("x:0")
  

9.求导

• 近似方法求导：

  • 什么是求导？？？

  求导是数学计算中的一个计算方法，它的定义就是，当自变量的增量趋于零时，因变量的增量与自变量的增量之商的极限。在一个函数存在导数时，称这个函数可导或者可微分。可导的函数一定连续。不连续的函数一定不可导。
  

  • 一元求导

  def f(x):
      # 3x^2 + 2x -1
      return 3. * x**2 + 2. * x -1
  def approximae_derivative(f, x, eps = 1e-3):
      return (f(x + eps) - f(x-eps)) / (2. * eps)
  print(approximae_derivative(f, 1.))# 7.999999999999119
  

  • 二元求导

  def g(x1, x2):
      return (x1 + 5) * (x2 ** 2)
  def approximae_gradiend(g, x1, x2, eps=1e-3):
      # g 对 x1 求导 需要把 x2 固定下来
      dg_x1 = approximae_derivative(lambda x: g(x, x2), x1, eps)
      # g 对 x2 求导 需要把 x1 固定下来
      dg_x2 = approximae_derivative(lambda x: g(x1, x), x2, eps)
      return dg_x1,dg_x2
  print(approximae_gradiend(g,2.,3.))# (8.999999999993236, 41.999999999994486)
  

• 在tensorflow求导数

  x1 = tf.Variable(2.0)
  x2 = tf.Variable(3.0)
  # persistent表示可以保存tape
  with tf.GradientTape(persistent=True) as tape:
      z = g(x1, x2)
  # x1偏导
  dz_x1 = tape.gradient(z, x1)
  print(dz_x1)
  # x2偏导
  dz_x2 = tape.gradient(z, x2)
  print(dz_x2)
  # 删除tape释放资源
  del tape
  """
  tf.Tensor(9.0, shape=(), dtype=float32)
  tf.Tensor(42.0, shape=(), dtype=float32)
  """
  

• 传入列表形式求偏导

  x1 = tf.Variable(2.0)
  x2 = tf.Variable(3.0)
  # persistent表示可以保存tape
  with tf.GradientTape() as tape:
      z = g(x1, x2)
  # x1偏导
  dz_x = tape.gradient(z, [x1, x2])
  print(dz_x)
  # [<tf.Tensor: shape=(), dtype=float32, numpy=9.0>, <tf.Tensor: shape=(), dtype=float32, numpy=42.0>]
  

• 两个目标函数对一个变量求导

  x = tf.Variable(5.0)
  with tf.GradientTape() as tape:
      z1 = 3 * x
      z2 = x ** 2
  tape.gradient([z1, z2], x)
  
  # <tf.Tensor: shape=(), dtype=float32, numpy=13.0>
  

• 二阶函数求导

  x1 = tf.Variable(2.0)
  x2 = tf.Variable(3.0)
  with tf.GradientTape(persistent=True) as outer_tape:
      with tf.GradientTape(persistent=True) as inner_tape:
          z = g(x1, x2)
      inner_grads = inner_tape.gradient(z, [x1, x2])
  outer_grads = [outer_tape.gradient(inner_grad, [x1, x2])
                for inner_grad in inner_grads]
  print(outer_grads)
  del inner_tape
  del outer_tape
  # 2 * 2矩阵
  """
  [[None, <tf.Tensor: shape=(), dtype=float32, numpy=6.0>], [<tf.Tensor: shape=(), dtype=float32, numpy=6.0>, <tf.Tensor: shape=(), dtype=float32, numpy=14.0>]]
  """
  

• 模拟梯度下降

  learning_rate = 0.1
  x = tf.Variable(0.0)
  for _ in range(100):
      with tf.GradientTape() as tape:
          z = f(x)
      dz_dx = tape.gradient(z, x)
      x.assign_sub(learning_rate * dz_dx)
  print(x)
  

• 与keras optimizer结合使用

  learning_rate = 0.1
  x = tf.Variable(0.0)
  
  optimizer = keras.optimizers.SGD(lr = learning_rate)
  
  
  for _ in range(100):
      with tf.GradientTape() as tape:
          z = f(x)
      dz_dx = tape.gradient(z, x)
      optimizer.apply_gradients([(dz_dx, x)])
  print(x)
  # <tf.Variable 'Variable:0' shape=() dtype=float32, numpy=-0.3333333>
  

10.Tf.Gradient 与 tf.keras结合使用

• 求差方函数

  metric = keras.metrics.MeanSquaredError()# 求差方函数
  # 下述相当图 （5 - 2）^2
  print(metric([5.], [2.]))# 9
  print(metric([0.],[1.]))# 5
  print(metric.result())# 5          上面函数进行了累加操作
  
  # 如果不想累加,重置。
  metric.reset_states()
  print(metric([2.], [6.]))# 16
  
  

• 手动求导进行回归问题求解

  
  # 实现步骤
  # 1. 遍历训练集
  # 2. 取出数据，计算梯度，apply更新梯度
  # 3. 最后验证集上验证
  
  
  
  # 变量定义
  epochs = 100
  batch_size = 32
  # 所有样本数
  steps_per_epoch = len(x_train_scaled) // batch_size
  optimizer = keras.optimizers.SGD()
  metric = keras.metrics.MeanSquaredError()# 求差方函数 函数形式为mse
  
  def random_batch(x, y, batch_size=32):
      idx = np.random.randint(n, len(x), size=batch_size)
      return x[idx], y[idx]
  
  
  
  model = keras.models.Sequential([
      keras.layers.Dense(30, activation="relu"),
      keras.layers.Dense(1)
  ])
  model.compile(loss="mean_squared_error", optimizer="sgd")
  
  for epoch in range(epochgs):
      metric.reset_states()
      for step in range(steps_per_epoch):
          x_batch, y_batch = random_batch(x_train_scaled, y_train,batch_size)
          with tf.GradientTape() as tape:
              # 获取预测值
              y_pred = model(x_batch)
              # 获取损失值
              loss = tf.reduce_mean(keras.losses.mean_squared_error(y_batch, y_pred))
              # 累计计算 metric
              metric(y_batch, y_pred)
          # 手动求梯度
          grads = tape.gradient(loss, model.variables)
          # 梯度与变量绑定
          grads_and vars = zip(grads, model.variables)
          # 更新梯度
          optimizer.apply_gradients(grads_and_vars)
          # 打印训练的mse
          print("\r Epoch", epoch, " train mse", metric.result().numpy(), end = " ")
      # 验证
      y_valid_pred = model(x_valid_scaled)
      valid_loss = tf.reduce_mean(keras.losses.mean_squared_error(y_valid_preed, y_valid))
      print("\t","valid mse:", valid_loss.numpy())