# pytorch-widedeep¶

A flexible package to combine tabular data with text and images using wide and deep models

Below there is an introduction to the architectures one can build using pytorch-widedeep. If you prefer to learn about the utilities and components go straight to corresponding sections in the Documentation.

## Introduction¶

pytorch-widedeep is based on Google’s Wide and Deep Algorithm.

In general terms, pytorch-widedeep is a package to use deep learning with tabular and multimodal data. In particular, is intended to facilitate the combination of text and images with corresponding tabular data using wide and deep models. With that in mind there are a number of architectures that can be implemented with just a few lines of code. The main components of those architectures are shown in the Figure below:

The dashed boxes in the figure represent optional, overall components, and the dashed lines indicate the corresponding connections, depending on whether or not certain components are present. For example, the dashed, blue-arrows indicate that the deeptabular, deeptext and deepimage components are connected directly to the output neuron or neurons (depending on whether we are performing a binary classification or regression, or a multi-class classification) if the optional deephead is not present. The components within the faded-pink rectangle are concatenated.

Note that it is not possible to illustrate the number of possible architectures and components available in pytorch-widedeep in one Figure. Therefore, for more details on possible architectures (and more) please, read this documentation, or see the Examples folders in the repo.

In math terms, and following the notation in the paper, the expression for the architecture without a deephead component can be formulated as:

Where ‘W’ are the weight matrices applied to the wide model and to the final activations of the deep models, $$a$$ are these final activations, and $${\phi}$$ (x) are the cross product transformations of the original features ‘x’. In case you are wondering what are “cross product transformations”, here is a quote taken directly from the paper: “For binary features, a cross-product transformation (e.g., “AND(gender=female, language=en)”) is 1 if and only if the constituent features (“gender=female” and “language=en”) are all 1, and 0 otherwise”. Finally, $${\sigma}$$ (.) is the activation function.

While if there is a deephead component, the previous expression turns into:

It is important to emphasize that each individual component, wide, deeptabular, deeptext and deepimage, can be used independently and in isolation. For example, one could use only wide, which is in simply a linear model. In fact, one of the most interesting functionalities in pytorch-widedeep would be the use of the deeptabular component on its own, i.e. what one might normally refer as Deep Learning for Tabular Data. Currently, pytorch-widedeep offers the following different models for that component:

1. TabMlp: a simple MLP that receives embeddings representing the categorical features, concatenated with the continuous features.

2. TabResnet: similar to the previous model but the embeddings are passed through a series of ResNet blocks built with dense layers.

3. TabNet: details on TabNet can be found in TabNet: Attentive Interpretable Tabular Learning

And the Tabformer family, i.e. Transformers for Tabular data:

4. TabTransformer: details on the TabTransformer can be found in TabTransformer: Tabular Data Modeling Using Contextual Embeddings.

5. SAINT: Details on SAINT can be found in SAINT: Improved Neural Networks for Tabular Data via Row Attention and Contrastive Pre-Training.

6. FT-Transformer: details on the FT-Transformer can be found in Revisiting Deep Learning Models for Tabular Data.

7. TabFastFormer: adaptation of the FastFormer for tabular data. Details on the Fasformer can be found in FastFormers: Highly Efficient Transformer Models for Natural Language Understanding

8. TabPerceiver: adaptation of the Perceiver for tabular data. Details on the Perceiver can be found in Perceiver: General Perception with Iterative Attention

Note that while there are scientific publications for the TabTransformer, SAINT and FT-Transformer, the TabFasfFormer and TabPerceiver are our own adaptation of those algorithms for tabular data.

For details on these models and their options please see the examples in the Examples folder and the documentation.

Finally, while I recommend using the wide and deeptabular models in pytorch-widedeep it is very likely that users will want to use their own models for the deeptext and deepimage components. That is perfectly possible as long as the the custom models have an attribute called output_dim with the size of the last layer of activations, so that WideDeep can be constructed. Again, examples on how to use custom components can be found in the Examples folder. Just in case pytorch-widedeep includes standard text (stack of LSTMs or GRUs) and image(pre-trained ResNets or stack of CNNs) models.