DATGAN

Directed Acyclic Tabular GAN (DATGAN) for integrating expert knowledge in synthetic tabular data generation.

• License: GPLv3
• Development Status: Alpha
• Homepage: https://github.com/glederrey/DATGAN

The preprint of the article for this model should be available on arXiv by mid-March.

Overview

The DATGAN is a synthesizer for tabular data. It uses LSTM cells to generate synthetic data for continuous and categorical variable types. In addition, a Directed Acyclic Graph (DAG) can be provided to represent the structure between the variables and help the model to perform better.

Requirements

The current version (v2.0.0) of the DATGAN works with Python 3.9 (earlier versions have not been tested) and Tensorflow 2. We, thus, recommend the user to set up a virtualenv.

Installation

We provide a complete installation guide using conda and setting up a virtualenv. Please follow this guide to properly set up everything and make sure that you can use the DATGAN as intended.

Testing the DATGAN

You can clone this repository and use the notebooks provided in the folder example to train the DATGAN and use the evaluation metrics provided in this repository.

Data Format

Input

The DATGAN uses tabular data loaded with the pandas library. This table must follow these rules:

• has no missing values
• has columns of types int, float, str or bool.
• each column contains data of only one type.

NOTE: It is important to identify which columns are considered continuous and which are considered categorical. For example, columns with discrete distributions have to be defined as continuous columns.

Output

The output of the DATGAN is a table of synthetic data with the same columns as the input table and as many rows as requested.

Tutorial

In this short tutorial we will guide you through a series of steps that will help you getting started with the most basic usage of DATGAN in order to generate samples from a given dataset.

NOTE: The following examples are also covered in a Jupyter notebook, which you can execute by running the following commands inside your virtualenv:

pip install jupyter
jupyter notebook example/training.ipynb

1. Load the data

The first step is to load the data wich we will use to fit the DATGAN. In the example, we provide a demo dataset, the CMAP dataset. You can load it using pandas. We also need to define which columns are considered continuous. For this, we simply define a list of str with the name of the variables that we consider as continuous.

import pandas as pd

df = pd.read_csv('./data/CMAP.csv', index_col=False)

continuous_columns = ["distance", "age", "departure_time"]

2. Create a DAG

The second steps consists in creating the DAG for the DATGAN. The DAG is created using the library networkx from Python. If you just want to test the model without any specific DAG, we recommend you to use a linear DAG.

Example of a DAG for the CMAP dataset:

import networkx as nx

graph = nx.DiGraph()
graph.add_edges_from([
    ("age", "license"),
    ("age", "education_level"),
    ("gender", "work_status"),
    ("education_level", "work_status"),
    ("education_level", "hh_income"),
    ("work_status", "hh_income"),
    ("hh_income", "hh_descr"),
    ("hh_income", "hh_size"),
    ("hh_size", "hh_vehicles"),
    ("hh_size", "hh_bikes"),
    ("work_status", "trip_purpose"),
    ("trip_purpose", "departure_time"),
    ("trip_purpose", "distance"),
    ("travel_dow", "choice"),
    ("distance", "choice"),
    ("departure_time", "choice"),
    ("hh_vehicles", "choice"),
    ("hh_bikes", "choice"),
    ("license", "choice"),
    ("education_level", "hh_size"),
    ("work_status", "hh_descr"),
    ("work_status", "hh_size"),
    ("hh_income", "hh_bikes"),
    ("hh_income", "hh_vehicles"),
    ("trip_purpose", "choice")
])

If you do not have any idea how to create your DAG, it is possible to not provide any DAG to the model. However, in this case, the model will define a linear DAG, i.e. each variable in the dataset is linked to the next one following the order of the columns. It can be useful to quickly test the model. However, it will reduce the performance of the model as shown in the article.

3. Create a DATGAN instance

The next step is to import DATGAN and create an instance of the model. There are no required parameters for the model. However, we advise you to set up the basic parameters such as the output folder (output), batch size (batch_size), and verbose level (verbose).

output_folder = './output/'
batch_size = 558

from datgan import DATGAN

datgan = DATGAN(output=output_folder, batch_size=batch_size, verbose=1)

NOTE: Setting up a suitable batch size is really important. A batch size too big will make the model crash due to memory error while one that is too small will make the model slower to train. Trials and errors are required depending on your hardware. In addition, it is good to find a batch size such that len(df) % batch_size is as small as possible since the last batch of data is dropped if it is smaller than the batch size.

4. Preprocess the data (optional)

The fourth step consists in preprocessing the data. This step is optional since it is automatically done in the next step if skipped right now. We propose to do the preprocessing in advance because it usually takes a bit of time. And if you want to try multiple parameters with the DATGAN, you do not have to preprocess the data every time. Therefore, it is possible to do it before fitting the model and saving it somewhere.

datgan.preprocess(df, continuous_columns, preprocessed_data_path='./encoded_data')

5. Fit the model

Once you have a DATGAN instance, you can call the method fit and passing the following parameters:

• data: the original DataFrame
• graph: the networkx DAG
• continuous_columns: the list of continuous columns
• preprocessed_data_path: the path to the preprocessed data if done in Step 4 or the path where to save them.

datgan.fit(df, graph, continuous_columns, preprocessed_data_path='./encoded_data')

6. Sample new data

Once the model has been fitted, you can generate new synthetic data by calling the function sample. You have to provide the desired number of samples.

samples = datgan.sample(len(df))
samples.age = np.round(samples.age)
samples.to_csv('./data/CMAP_synthetic.csv', index=False)

In this case, the column age is a discrete distribution. The DATGAN cannot provide such data type for the moment, we, thus, advise you to treat such column as continuous and, then, round the values.

7. Save and load a model

In the steps above we saw that the fitting process can take a lot of time, so we probably would like to avoid having to fit every we want to generate samples. We advise the use to save checkpoints of the model while it is training. However, if you do not want to do that, the model will always save the latest checkpoint once it has finished training. You can, thus, load it at any time afterwards.

In order to load the model, you can simply call the function load with the parameters used while fitting the model. In order to save memory, we only save the parameters of the Generator and Discriminator. Therefore, more information is required to load the model.

new_datgan = datgan.load(df, graph, continuous_columns, preprocessed_data_path='./encoded_data')

At this point we can use this model instance to generate more samples.

Model parameters

If you want to change the default behavior of DATGAN, such as using different batch size or the total number of epochs, you can do so by passing different arguments when creating the DATGAN instance.

Loading the model

Name	Type	Default	Explanation
loss_function	str	None	Name of the loss function to be used. If not specified, it will choose between 'WGAN' and 'WGGP' depending on the ratio of continuous and categorical columns. Only accepts the values 'SGAN', 'WGAN', and 'WGGP'.
label_smoothing	str	'TS'	Type of label smoothing. Only accepts the values 'TS', 'OS', and 'NO'.
output	str	'./output'	Path to store the model and its artifacts.
gpu	int	None	Model will automatically try to use GPU if tensorflow can use CUDA. However, this parameter allows you to choose which GPU you want to use.
num_epochs	int	100	Number of epochs to use during training.
batch_size	int	500	Size of the batch to feed the model at each step.
save_checkpoints	bool	True	Whether to store checkpoints of the model after each training epoch.
restore_session	bool	True	Whether continue training from the last checkpoint.
learning_rate	float	None	Learning rate. If set to None, the value will be set according to the chosen loss function.
g_period	int	None	Every g_period steps, train the generator once. (Used to train the discriminator more than the generator) By default, it will choose values according the chosen loss function.
l2_reg	bool	None	Tell the model to use L2 regularization while training both NNs. By default, it only applies the L2 regularization when using the SGAN loss function.
z_dim	int	200	Dimension of the noise vector used as an input to the generator.
num_gen_rnn	int	100	Size of the hidden units in the LSTM cell.
num_gen_hidden	int	50	Size of the hidden layer used on the output of the generator to act as a convolution.
num_dis_layers	int	1	Number of layers for the discriminator.
num_dis_hidden	int	100	Size of the hidden layers in the discriminator.
noise	float	0.2	Upper bound to the gaussian noise added to with the label smoothing. (only used if label_smoothing is set to 'TS' or 'OS')
verbose	int	1	Level of verbose. 0 means no print, 1 means that some details will be printed, 2 is mostly used for debugging purpose.

Sampling synthetic data

When sampling the synthetic data (DATGAN.sample), you can choose between multiple sampling strategies.

Name	Type	Default	Explanation
sampling	str	SS	Type of sampling to use. Only accepts the following values: 'SS', 'SA', 'AS', and 'AA'.

S means we are using simulation to sample the data, A means that we are using argmax. The first letter corresponds to continuous variables and the second to categorical variables. Therefore, SA means we're using simulation for continuous variables and argmax for categorical variables.

Tips and tricks

While the DATGAN model will automatically choose the parameters of the model if none are provided, we highly recommend the user to "play" with them. The most important ones are the following:

• loss_function Generally, the WGAN loss function works better on datasets with more categorical columns than continuous. It is the contrary for the WGGP loss. The SGAN loss seems to perform a bit less good than the other two in the specific cases. However, it seems to perform ok in any cases.
• g_period This parameter is especially important when using either the WGAN or the WGGP loss. Generally, the latter requires a lot more training of the discriminator than the previous. However, it might be interesting to test different values to see which one leads to the best results.
• l2_reg The L2 regularization is "mandatory" for the SGAN loss and "forbidden" for the WGAN loss. The user can test these other configurations, but it will lead to worse results. However, for the WGGP loss, there are no specific rules whether to apply it or not. Therefore, it might be interesting to test this parameter as well.
• learning_rate It has been fixed depending on the loss function. However, as for any optimization problem, playing with the learning rate to find the optimal value is always important.

Acknowledgements

We would like to thank the authors of the TGAN article, Lei Xu and Kalyan Veeramachaneni, as well as all the contributors of the TGAN Github repository. This model has greatly inspired the ideas behind the DATGAN and we have used their code as a starting point to write our model.

Citing DATGAN

If you use DATGAN or its evaluation metrics, please cite the following work:

Gael Lederrey, Tim Hillel, Michel Bierlaire. 2022. DATGAN: Integrating expert knowledge into deep learning for synthetic tabular data. ArXiv preprint

FULL CITATION COMING SOON!

The original code for this article can be found in this Github repository: https://github.com/glederrey/SynthPop.