The TF estimators are high-level pre-made blocks which help you perform quickly some learning tasks:
- you can run Estimator-based models on a local host or on a distributed multi-server environment without changing your model. Furthermore, you can run Estimator-based models on CPUs, GPUs, or TPUs without recoding your model.
- estimators simplify sharing implementations between model developers.
- you can develop a state of the art model with high-level intuitive code. In short, it is generally much easier to create models with Estimators than with the low-level TensorFlow APIs.
- estimators are themselves built on
tf.keras.layers, which simplifies customization. - estimators build the graph for you.
- estimators provide a safe distributed training loop that controls how and when to:
- build the graph
- initialize variables
- load data
- handle exceptions
- create checkpoint files and recover from failures
- save summaries for TensorBoard
When writing an application with Estimators, you have to separate the data input pipeline from the model, which simplifies experiments with different data sets.
Below is a straightforward example of a linear regression with estimators. It highlights the general workflow.
You need of course to import some namespaces
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import tensorflow as tf tf.enable_eager_execution() assert tf.executing_eagerly() import tensorflow.contrib.eager as tfe # too much info otherwise tf.logging.set_verbosity(tf.logging.ERROR) import numpy as np import matplotlib.pyplot as plt import seaborn as sea sea.set() sea.set %matplotlib inline |
and define some data
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X = np.arange(0,100) np.random.shuffle(X) # set a linear y = ax+b y = 3*X +2 + np.random.normal(size=[100]) |
The feature columns go into the definition of the estimator:
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column = tf.feature_column.numeric_column('x') lin_reg = tf.estimator.LinearRegressor(feature_columns=[column]) |
and the usage of input functions allows you to decouple input from model
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train_input = tf.estimator.inputs.numpy_input_fn( x={"x": X}, y=y, shuffle=False,num_epochs=2500,batch_size=1) lin_reg.train(train_input) |
To predict things you use input functions as well
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predict_input = tf.estimator.inputs.numpy_input_fn( x={"x": X}, num_epochs=1, shuffle=False) results = list(lin_reg.predict(predict_input)) fig, ax = plt.subplots() sea.regplot(X,y, ax=ax) ax2 = ax.twinx() sea.regplot(X, np.array([x["predictions"][0] for x in list(results) ]) , ax=ax2, color='r') |
and it’s clear that estimators are the fastest road to results in terms of API mechanics. Next to Keras and the low-level API the estimators is a third API layer in TensorFlow. Whether this approach is the best depends on your context:
- the checkpoints mechanism related to model restoration should, in particular, be considered in contrast to the non-estimator approaches
- the (dis)advantages of creating custom estimators
- the flexibility of Keras versus the flexibility of estimator pipelines (also in the context of serving models)
Estimators definitely turn TensorFlow into something close to Scikit-Learn but whether you should use TF as a replacement for sklearn. Well, probably not.
The whole estimator stack is also available in R and works similarly, maybe even easier:
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library(tfestimators) response <- function() "Species" features <- function() setdiff(names(iris), response()) # split into train, test datasets set.seed(123) partitions <- modelr::resample_partition(iris, c(test = 0.2, train = 0.8)) iris_train <- as.data.frame(partitions$train) iris_test <- as.data.frame(partitions$test) # construct feature columns feature_columns <- feature_columns( column_numeric(features()) ) # construct classifier classifier <- dnn_classifier( feature_columns = feature_columns, hidden_units = c(10, 20, 10), n_classes = 3 ) # construct input function iris_input_fn <- function(data) { input_fn(data, features = features(), response = response()) } # train classifier with training dataset train(classifier, input_fn = iris_input_fn(iris_train)) # valuate with test dataset predictions <- predict(classifier, input_fn = iris_input_fn(iris_test)) evaluation <- evaluate(classifier, input_fn = iris_input_fn(iris_test)) |
The TensorFlow API for R is actually very nicely documented and complements well the Python docs.
