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Python library for distributed AI processing pipelines, using swappable scheduler backends.
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README.rst

Wordbatch 1.4.2

Overview

Python library for distributed AI processing pipelines, using swappable scheduler backends.

Wordbatch parallelizes task pipelines as minibatches processed by a chosen scheduler backend. This allows the user to develop AI programs on a local workstation or laptop, and scale the same solution on a cluster or the cloud, simply by changing the pipeline backend to a distributed scheduler such as Spark, Dask or Ray. A backend can be chosen based on performance characteristics on a particular task, and swapped for different situations. For example, an AI model can be trained using a distributed backend, and then debugged or deployed using a single serial process.

The library is organized around the orchestrator class Batcher, and Sklearn-compatible components, split into Pipelines, Transformers, Extractors and Models. These extend the Scikit-learn API with a fit_partial()-method, that enables transformers and models to be used in a streaming fashion. The current set of components has been developed mostly for text processing tasks, but components for other domains can be developed based on the available classes.

Requirements

Linux / Windows / macOS. Python 3.6 / 3.7

Installation

pip install wordbatch

macOS: compile using GCC-7 (https://github.com/anttttti/Wordbatch/issues/1)

linux: make sure GCC and its required libraries are installed before installing Wordbatch | sudo apt install gcc | sudo apt-get update | sudo apt-get install --reinstall build-essential

Getting started

from wordbatch.models import FTRL
from wordbatch.extractors import WordBag
from wordbatch.pipelines import WordBatch
from wordbatch.batcher import Batcher

wb= WordBatch(extractor=WordBag(hash_ngrams=0, norm= 'l2', tf= 'binary', idf= 50.0),
batcher=Batcher(backend="multiprocessing"))

clf= FTRL(alpha=1.0, beta=1.0, L1=0.00001, L2=1.0, D=2 ** 25, iters=1)

train_texts= ["Cut down a tree with a herring? It can't be done.",
"Don't say that word.",
"How can we not say the word if you don't tell us what it is?"]
train_labels= [1, 0, 1]
test_texts= ["Wait! I said it! I said it! Ooh! I said it again!"]

clf.fit(wb.fit_transform(train_texts), train_labels)
print(clf.predict(wb.transform(test_texts)))

import ray
ray.init()
wb.batcher.backend= "ray"
wb.batcher.backend_handle= ray

clf.fit(wb.fit_transform(train_texts), train_labels)
print(clf.predict(wb.transform(test_texts)))

Components

Batcher

Batcher orchestrates MapReduce processing of tasks using a backend, by splitting input data into separately processed minibatches. Currently three local (serial, multiprocessing, Loky) and three distributed backends (Spark, Dask, Ray) are supported. Some distributed backends will process the tasks concurrently as a graph of lazily evaluated futures, with Batcher dynamically sending the graph for the backend to process. All three supported distributed backends allow real time monitoring of the processing pipeline using the backend's own GUI.

Pipelines

Pipelines are classes that send functions, methods and classes to Batcher for processing. Unlike other components in Wordbatch, pipelines contain a reference to Batcher, and are never referenced themselves in the calls sent to Batcher. This prevents trying to serialize and send the backend handle itself. The simplest pipeline is Apply, which processes a function or method over the input data row-by-row. WordBatch is a full complex pipeline for text processing, with optional steps such as text normalization, spelling correction, stemming, feature extraction, and LZ4-caching of results.

Transformers

Transformers are transformer classes extending the Scikit-learn API, by accepting a Batcher instance as argument of fit and transform methods. Transformers won't store Batcher references, allowing the transformer objects to be sent to distributed workers. This allows transformers to do MapReduce operations as part of its methods, for example gathering a dictionary of words from data when fitting a Dictionary. The current set of transformers are text-specific classes, such as Dictionary, Tokenizer and TextNormalizer.

Extractors

Extractors are transformer classes which don't directly call Batcher. Since extractors can't call Batcher directly, they are mostly immutable and used for their transform() method calls distributed using a pipeline. The current set of extractors is Cython-optimized, and aside from PandasHash intended for text feature extraction. These are:

  • WordHash is wrapper for Scikit-learn HashingVectorizer, extended with option for LZ4-caching
  • WordBag is a flexible alternative to Wordhash, with options such as IDF and per n-gram order weighting
  • WordSeq provides sequences of word integers, as used by deep learning language models
  • WordVec embeds words into word vector representations
  • PandasHash extracts hashed features from a Pandas DataFrame, similar to VowpalWabbit's feature extraction

Models

Models are predictive models such as classifiers. Similar to extractors, they don't directly call Batcher, but are Scikit-learn compatible and distributed using a pipeline if needed. Currently four OpenMP-multithreaded L1&L2-regularized online learning models are provided, for single-label regression and classification:

  • FTRL : Linear model Proximal-FTRL that has become the most popular algorithm for online learning of linear models in Kaggle competions. The Cython-optimized implementation should be the fastest available version of FTRL.
  • FM_FTRL : Factorization Machines. Linear effects estimated with FTRL and factor effects estimated with adaptive SGD. Prediction and estimation multithreaded across factors.
  • NN_Relu_H1 : Neural Network with 1 hidden layer and Rectified Linear Unit activations, estimated with adaptive SGD. Prediction and estimation multithreaded across hidden layer.
  • NN_Relu_H2: Neural Network with 2 hidden layers and Rectified Linear Unit activations, estimated with adaptive SGD. Prediction multithreaded across 2nd hidden layer, estimation across 1st hidden layer outputs.

The adaptive SGD optimizer works like Adagrad, but pools the adaptive learning rates across hidden nodes using the same feature. This makes learning more robust and requires less memory. FM_FTRL uses AVX2-optimization, so that processors supporting AVX2 will run the factorization model up to four times faster.

Example scripts

The directory /scripts/ contains scripts for demonstrating and testing basic uses of the toolkit. To run the scripts one should first install the dependencies: Keras, NLTK, TextBlob, Pandas, Ray, Dask Distributed and PySpark. The scripts also use the TripAdvisor dataset (http://times.cs.uiuc.edu/~wang296/Data/), and the precomputed word embeddings glove.twitter.27B.100d and glove.6B.50d (http://nlp.stanford.edu/projects/glove/). Test data from Crowdflower Open data & Kaggle is provided in the /data directory.

Airline Classification Example

classify_airline_sentiment.py shows training and combining predictions with four classifier scripts that use the Wordbatch extractors and models: wordhash_regressor.py, wordbag_regressor.py, wordseq_regressor.py and wordvec_regressor.py. The header part of the script can be modified to choose the backend. By default Ray is used and passed to the other scripts.

Backends Benchmark Example

backends_benchmark.py shows how to benchmark different backends on two simple pipeline tasks: using ApplyBatch with Scikit-learn HashingVectorizer, and running WordBatch Pipeline with most of its possible processing steps. Dask and Spark are commented out by default, as these need command-line configuration. All three distributed backends can be configured to run across a distributed cluster, as done in the commented-out code.

Contributors

Antti Puurula

Anders Topper

Cheng-Tsung Liu

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