Artificial Intelligence

Posit AI Weblog: TensorFlow 2.0 is right here

August 15, 2024
roosho

Posit AI Weblog: TensorFlow 2.0 is right here

The wait is over – TensorFlow 2.0 (TF 2) is now formally right here! What does this imply for us, customers of R packages keras and/or tensorflow, which, as we all know, depend on the Python TensorFlow backend?

Earlier than we go into particulars and explanations, right here is an all-clear, for the involved consumer who fears their keras code would possibly turn into out of date (it gained’t).

Don’t panic

  • If you’re utilizing keras in commonplace methods, similar to these depicted in most code examples and tutorials seen on the net, and issues have been working wonderful for you in current keras releases (>= 2.2.4.1), don’t fear. Most every part ought to work with out main adjustments.
  • If you’re utilizing an older launch of keras (< 2.2.4.1), syntactically issues ought to work wonderful as effectively, however you’ll want to test for adjustments in habits/efficiency.

And now for some information and background. This put up goals to do three issues:

  • Clarify the above all-clear assertion. Is it actually that easy – what precisely is happening?
  • Characterize the adjustments led to by TF 2, from the perspective of the R consumer.
  • And, maybe most apparently: Check out what’s going on, within the r-tensorflow ecosystem, round new performance associated to the appearance of TF 2.

Some background

So if all nonetheless works wonderful (assuming commonplace utilization), why a lot ado about TF 2 in Python land?

The distinction is that on the R aspect, for the overwhelming majority of customers, the framework you used to do deep studying was keras. tensorflow was wanted simply often, or in no way.

Between keras and tensorflow, there was a transparent separation of duties: keras was the frontend, relying on TensorFlow as a low-level backend, identical to the unique Python Keras it was wrapping did. . In some instances, this result in folks utilizing the phrases keras and tensorflow virtually synonymously: Possibly they stated tensorflow, however the code they wrote was keras.

Issues have been completely different in Python land. There was unique Python Keras, however TensorFlow had its personal layers API, and there have been quite a lot of third-party high-level APIs constructed on TensorFlow.
Keras, in distinction, was a separate library that simply occurred to depend on TensorFlow.

So in Python land, now we have now a giant change: With TF 2, Keras (as integrated within the TensorFlow codebase) is now the official high-level API for TensorFlow. To carry this throughout has been a serious level of Google’s TF 2 info marketing campaign because the early phases.

As R customers, who’ve been specializing in keras on a regular basis, we’re primarily much less affected. Like we stated above, syntactically most every part stays the way in which it was. So why differentiate between completely different keras variations?

When keras was written, there was unique Python Keras, and that was the library we have been binding to. Nonetheless, Google began to include unique Keras code into their TensorFlow codebase as a fork, to proceed improvement independently. For some time there have been two “Kerases”: Unique Keras and tf.keras. Our R keras provided to change between implementations , the default being unique Keras.

In keras launch 2.2.4.1, anticipating discontinuation of unique Keras and desirous to prepare for TF 2, we switched to utilizing tf.keras because the default. Whereas at first, the tf.keras fork and unique Keras developed kind of in sync, the most recent developments for TF 2 introduced with them larger adjustments within the tf.keras codebase, particularly as regards optimizers.
This is the reason, if you’re utilizing a keras model < 2.2.4.1, upgrading to TF 2 you’ll want to test for adjustments in habits and/or efficiency.

That’s it for some background. In sum, we’re joyful most current code will run simply wonderful. However for us R customers, one thing should be altering as effectively, proper?

TF 2 in a nutshell, from an R perspective

Actually, essentially the most evident-on-user-level change is one thing we wrote a number of posts about, greater than a 12 months in the past . By then, keen execution was a brand-new possibility that needed to be turned on explicitly; TF 2 now makes it the default. Together with it got here customized fashions (a.ok.a. subclassed fashions, in Python land) and customized coaching, making use of tf$GradientTape. Let’s discuss what these termini seek advice from, and the way they’re related to R customers.

Keen Execution

In TF 1, it was all in regards to the graph you constructed when defining your mannequin. The graph, that was – and is – an Summary Syntax Tree (AST), with operations as nodes and tensors “flowing” alongside the perimeters. Defining a graph and operating it (on precise information) have been completely different steps.

In distinction, with keen execution, operations are run immediately when outlined.

Whereas this can be a more-than-substantial change that will need to have required a lot of sources to implement, in the event you use keras you gained’t discover. Simply as beforehand, the everyday keras workflow of create mannequin -> compile mannequin -> prepare mannequin by no means made you concentrate on there being two distinct phases (outline and run), now once more you don’t need to do something. Although the general execution mode is raring, Keras fashions are skilled in graph mode, to maximise efficiency. We’ll discuss how that is carried out partially 3 when introducing the tfautograph bundle.

If keras runs in graph mode, how will you even see that keen execution is “on”? Nicely, in TF 1, once you ran a TensorFlow operation on a tensor , like so

that is what you noticed:

Tensor("Cumprod:0", form=(5,), dtype=int32)

To extract the precise values, you needed to create a TensorFlow Session and run the tensor, or alternatively, use keras::k_eval that did this beneath the hood:

[1]   1   2   6  24 120

With TF 2’s execution mode defaulting to keen, we now routinely see the values contained within the tensor: 

tf.Tensor([  1   2   6  24 120], form=(5,), dtype=int32)

In order that’s keen execution. In our final 12 months’s Keen-category weblog posts, it was at all times accompanied by customized fashions, so let’s flip there subsequent.

Customized fashions

As a keras consumer, in all probability you’re accustomed to the sequential and practical kinds of constructing a mannequin. Customized fashions permit for even larger flexibility than functional-style ones. Try the documentation for easy methods to create one.

Final 12 months’s collection on keen execution has loads of examples utilizing customized fashions, that includes not simply their flexibility, however one other essential side as effectively: the way in which they permit for modular, easily-intelligible code.

Encoder-decoder situations are a pure match. When you have seen, or written, “old-style” code for a Generative Adversarial Community (GAN), think about one thing like this as an alternative:

with(tf$GradientTape() %as% gen_tape, { with(tf$GradientTape() %as% disc_tape, {
  
  # first, it is the generator's name (yep pun supposed)
  generated_images <- generator(noise)
  # now the discriminator provides its verdict on the actual photos 
  disc_real_output <- discriminator(batch, coaching = TRUE)
  # in addition to the pretend ones
  disc_generated_output <- discriminator(generated_images, coaching = TRUE)
  
  # relying on the discriminator's verdict we simply obtained,
  # what is the generator's loss?
  gen_loss <- generator_loss(disc_generated_output)
  # and what is the loss for the discriminator?
  disc_loss <- discriminator_loss(disc_real_output, disc_generated_output)
}) })

# now exterior the tape's context compute the respective gradients
gradients_of_generator <- gen_tape$gradient(gen_loss, generator$variables)
gradients_of_discriminator <- disc_tape$gradient(disc_loss, discriminator$variables)
 
# and apply them!
generator_optimizer$apply_gradients(
  purrr::transpose(record(gradients_of_generator, generator$variables)))
discriminator_optimizer$apply_gradients(
  purrr::transpose(record(gradients_of_discriminator, discriminator$variables)))

Once more, evaluate this with pre-TF 2 GAN coaching – it makes for a lot extra readable code.

As an apart, final 12 months’s put up collection could have created the impression that with keen execution, you have to make use of customized (GradientTape) coaching as an alternative of Keras-style match. Actually, that was the case on the time these posts have been written. At this time, Keras-style code works simply wonderful with keen execution.

So now with TF 2, we’re in an optimum place. We can use customized coaching once we wish to, however we don’t need to if declarative match is all we’d like.

That’s it for a flashlight on what TF 2 means to R customers. We now have a look round within the r-tensorflow ecosystem to see new developments – recent-past, current and future – in areas like information loading, preprocessing, and extra.

New developments within the r-tensorflow ecosystem

These are what we’ll cowl:

  • tfdatasets: Over the current previous, tfdatasets pipelines have turn into the popular method for information loading and preprocessing.
  • function columns and function specs: Specify your options recipes-style and have keras generate the satisfactory layers for them.
  • Keras preprocessing layers: Keras preprocessing pipelines integrating performance similar to information augmentation (at present in planning).
  • tfhub: Use pretrained fashions as keras layers, and/or as function columns in a keras mannequin.
  • tf_function and tfautograph: Pace up coaching by operating components of your code in graph mode.

tfdatasets enter pipelines

For two years now, the tfdatasets bundle has been out there to load information for coaching Keras fashions in a streaming method.

Logically, there are three steps concerned:

  1. First, information needs to be loaded from some place. This could possibly be a csv file, a listing containing photos, or different sources. On this current instance from Picture segmentation with U-Web, details about file names was first saved into an R tibble, after which tensor_slices_dataset was used to create a dataset from it:
information <- tibble(
  img = record.recordsdata(right here::right here("data-raw/prepare"), full.names = TRUE),
  masks = record.recordsdata(right here::right here("data-raw/train_masks"), full.names = TRUE)
)

information <- initial_split(information, prop = 0.8)

dataset <- coaching(information) %>%  
  tensor_slices_dataset()
  1. As soon as we have now a dataset, we carry out any required transformations, mapping over the batch dimension. Persevering with with the instance from the U-Web put up, right here we use capabilities from the tf.picture module to (1) load photos in keeping with their file kind, (2) scale them to values between 0 and 1 (changing to float32 on the identical time), and (3) resize them to the specified format:
dataset <- dataset %>%
  dataset_map(~.x %>% list_modify(
    img = tf$picture$decode_jpeg(tf$io$read_file(.x$img)),
    masks = tf$picture$decode_gif(tf$io$read_file(.x$masks))[1,,,][,,1,drop=FALSE]
  )) %>% 
  dataset_map(~.x %>% list_modify(
    img = tf$picture$convert_image_dtype(.x$img, dtype = tf$float32),
    masks = tf$picture$convert_image_dtype(.x$masks, dtype = tf$float32)
  )) %>% 
  dataset_map(~.x %>% list_modify(
    img = tf$picture$resize(.x$img, measurement = form(128, 128)),
    masks = tf$picture$resize(.x$masks, measurement = form(128, 128))
  ))

Notice how as soon as you understand what these capabilities do, they free you of a number of considering (bear in mind how within the “previous” Keras strategy to picture preprocessing, you have been doing issues like dividing pixel values by 255 “by hand”?)

  1. After transformation, a 3rd conceptual step pertains to merchandise association. You’ll usually wish to shuffle, and also you actually will wish to batch the information:
 if (prepare) {
    dataset <- dataset %>% 
      dataset_shuffle(buffer_size = batch_size*128)
  }

dataset <- dataset %>%  dataset_batch(batch_size)

Summing up, utilizing tfdatasets you construct a pipeline, from loading over transformations to batching, that may then be fed on to a Keras mannequin. From preprocessing, let’s go a step additional and have a look at a brand new, extraordinarily handy solution to do function engineering.

Characteristic columns and have specs

Characteristic columns
as such are a Python-TensorFlow function, whereas function specs are an R-only idiom modeled after the favored recipes bundle.

All of it begins off with making a function spec object, utilizing system syntax to point what’s predictor and what’s goal:

library(tfdatasets)
hearts_dataset <- tensor_slices_dataset(hearts)
spec <- feature_spec(hearts_dataset, goal ~ .)

That specification is then refined by successive details about how we wish to make use of the uncooked predictors. That is the place function columns come into play. Completely different column varieties exist, of which you’ll be able to see a couple of within the following code snippet:

spec <- feature_spec(hearts, goal ~ .) %>% 
  step_numeric_column(
    all_numeric(), -cp, -restecg, -exang, -intercourse, -fbs,
    normalizer_fn = scaler_standard()
  ) %>% 
  step_categorical_column_with_vocabulary_list(thal) %>% 
  step_bucketized_column(age, boundaries = c(18, 25, 30, 35, 40, 45, 50, 55, 60, 65)) %>% 
  step_indicator_column(thal) %>% 
  step_embedding_column(thal, dimension = 2) %>% 
  step_crossed_column(c(thal, bucketized_age), hash_bucket_size = 10) %>%
  step_indicator_column(crossed_thal_bucketized_age)

spec %>% match()

What occurred right here is that we instructed TensorFlow, please take all numeric columns (moreover a couple of ones listed exprès) and scale them; take column thal, deal with it as categorical and create an embedding for it; discretize age in keeping with the given ranges; and eventually, create a crossed column to seize interplay between thal and that discretized age-range column.

That is good, however when creating the mannequin, we’ll nonetheless need to outline all these layers, proper? (Which might be fairly cumbersome, having to determine all the precise dimensions…)
Fortunately, we don’t need to. In sync with tfdatasets, keras now supplies layer_dense_features to create a layer tailored to accommodate the specification.

And we don’t must create separate enter layers both, resulting from layer_input_from_dataset. Right here we see each in motion:

enter <- layer_input_from_dataset(hearts %>% choose(-goal))

output <- enter %>% 
  layer_dense_features(feature_columns = dense_features(spec)) %>% 
  layer_dense(models = 1, activation = "sigmoid")

From then on, it’s simply regular keras compile and match. See the vignette for the whole instance. There is also a put up on function columns explaining extra of how this works, and illustrating the time-and-nerve-saving impact by evaluating with the pre-feature-spec method of working with heterogeneous datasets.

As a final merchandise on the subjects of preprocessing and have engineering, let’s have a look at a promising factor to return in what we hope is the close to future.

Keras preprocessing layers

Studying what we wrote above about utilizing tfdatasets for constructing a enter pipeline, and seeing how we gave a picture loading instance, you will have been questioning: What about information augmentation performance out there, traditionally, via keras? Like image_data_generator?

This performance doesn’t appear to suit. However a nice-looking resolution is in preparation. Within the Keras group, the current RFC on preprocessing layers for Keras addresses this subject. The RFC remains to be beneath dialogue, however as quickly because it will get carried out in Python we’ll observe up on the R aspect.

The concept is to supply (chainable) preprocessing layers for use for information transformation and/or augmentation in areas similar to picture classification, picture segmentation, object detection, textual content processing, and extra. The envisioned, within the RFC, pipeline of preprocessing layers ought to return a dataset, for compatibility with tf.information (our tfdatasets). We’re undoubtedly trying ahead to having out there this form of workflow!

Let’s transfer on to the subsequent subject, the widespread denominator being comfort. However now comfort means not having to construct billion-parameter fashions your self!

Tensorflow Hub and the tfhub bundle

Tensorflow Hub is a library for publishing and utilizing pretrained fashions. Current fashions will be browsed on tfhub.dev.

As of this writing, the unique Python library remains to be beneath improvement, so full stability just isn’t assured. That however, the tfhub R bundle already permits for some instructive experimentation.

The normal Keras concept of utilizing pretrained fashions usually concerned both (1) making use of a mannequin like MobileNet as a complete, together with its output layer, or (2) chaining a “customized head” to its penultimate layer . In distinction, the TF Hub concept is to make use of a pretrained mannequin as a module in a bigger setting.

There are two predominant methods to perform this, particularly, integrating a module as a keras layer and utilizing it as a function column. The tfhub README reveals the primary possibility:

library(tfhub)
library(keras)

enter <- layer_input(form = c(32, 32, 3))

output <- enter %>%
  # we're utilizing a pre-trained MobileNet mannequin!
  layer_hub(deal with = "https://tfhub.dev/google/tf2-preview/mobilenet_v2/feature_vector/2") %>%
  layer_dense(models = 10, activation = "softmax")

mannequin <- keras_model(enter, output)

Whereas the tfhub function columns vignette illustrates the second:

spec <- dataset_train %>%
  feature_spec(AdoptionSpeed ~ .) %>%
  step_text_embedding_column(
    Description,
    module_spec = "https://tfhub.dev/google/universal-sentence-encoder/2"
    ) %>%
  step_image_embedding_column(
    img,
    module_spec = "https://tfhub.dev/google/imagenet/resnet_v2_50/feature_vector/3"
  ) %>%
  step_numeric_column(Age, Charge, Amount, normalizer_fn = scaler_standard()) %>%
  step_categorical_column_with_vocabulary_list(
    has_type("string"), -Description, -RescuerID, -img_path, -PetID, -Title
  ) %>%
  step_embedding_column(Breed1:Well being, State)

Each utilization modes illustrate the excessive potential of working with Hub modules. Simply be cautioned that, as of at the moment, not each mannequin printed will work with TF 2.

tf_function, TF autograph and the R bundle tfautograph

As defined above, the default execution mode in TF 2 is raring. For efficiency causes nonetheless, in lots of instances will probably be fascinating to compile components of your code right into a graph. Calls to Keras layers, for instance, are run in graph mode.

To compile a perform right into a graph, wrap it in a name to tf_function, as carried out e.g. within the put up Modeling censored information with tfprobability:

run_mcmc <- perform(kernel) {
  kernel %>% mcmc_sample_chain(
    num_results = n_steps,
    num_burnin_steps = n_burnin,
    current_state = tf$ones_like(initial_betas),
    trace_fn = trace_fn
  )
}

# essential for efficiency: run HMC in graph mode
run_mcmc <- tf_function(run_mcmc)

On the Python aspect, the tf.autograph module routinely interprets Python management circulate statements into applicable graph operations.

Independently of tf.autograph, the R bundle tfautograph, developed by Tomasz Kalinowski, implements management circulate conversion immediately from R to TensorFlow. This allows you to use R’s if, whereas, for, break, and subsequent when writing customized coaching flows. Try the bundle’s intensive documentation for instructive examples!

Conclusion

With that, we finish our introduction of TF 2 and the brand new developments that encompass it.

When you have been utilizing keras in conventional methods, how a lot adjustments for you is especially as much as you: Most every part will nonetheless work, however new choices exist to write down extra performant, extra modular, extra elegant code. Specifically, try tfdatasets pipelines for environment friendly information loading.

In case you’re a complicated consumer requiring non-standard setup, take a look into customized coaching and customized fashions, and seek the advice of the tfautograph documentation to see how the bundle may also help.

In any case, keep tuned for upcoming posts displaying a number of the above-mentioned performance in motion. Thanks for studying!