This repository contains a Keras implementation of an encoder-decoder LSTM architecture for sequence-to-sequence spelling correction. The character-level spell checker is trained on unigram tokens derived from a vocabulary of more than 466k 33k unique English words. After 12 one hour of training, the speller achieves an accuracy performance of 96.7% 97.6% on a validation set comprised of more than 26k tokens.

Input sentence:
> The rabbit holV ewnt straight on liek a tnnel ofr some way any then dipped suddnely down so suddnenly tat Alice had nobt a moment to think aPout stopipng herself before she found hersefl falling dow a verZy deeup wLell

Decoded sentence:
> The rabbit hole went straight on like a tunnel for some way any then dipped suddenly drown so suddenly tat Alice had nob a moment to think Pout stopping herself before she found herself falling down a very deep well

Target sentence:
> The rabbit hole went straight on like a tunnel for some way and then dipped suddenly down so suddenly that Alice had not a moment to think about stopping herself before she found herself falling down a very deep well

Some ideas for further improvement on speller performance:

• Implement an attention mechanism
• Incorporate beam search as part of the loss evaluation
• Extend to high-order ngrams to capture intra-word contexts

The code is tested on Ubuntu 16.04 with the following components:

• Anaconda Python 3.6
• Keras 2.2.4 using TensorFlow GPU 1.12.0 backend
• CUDA 9.1 with CuDNN 7.1

• Intel Xeon CPU with 32 cores
• 64GB of system RAM
• NVIDIA GeForce GTX TITAN X GPU with 12GB of VRAM

The idea behind this project is inspired by this blog post, with several distinct enhancements in this implementation, such as teacher forcing, that result in much faster convergence and better performance.