mixupy 0.1.2

Data augmentation with the mixup method

mixupy

mixupy is a python package for data-augmentation inspired by mixup: Beyond Empinical Risk Minimization

If you like mixupy, give it a star, or fork it and contribute!

Usage

Create additional training data for the iris dataset:

import numpy as np
import pandas as pd
from mixupy import mixup

# Use 'iris' dataset from seaborn package
import seaborn as sns
iris = sns.load_dataset('iris')

# One-hot encode species column
iris_df = pd.get_dummies(iris, columns=['species'], prefix='', prefix_sep='')
iris_df

# Strictly speaking this is 'input mixup' (see Details section below)
set.seed(42)
iris_mix = mixup(iris_df)
iris_mix.describe()
iris_df.describe()

# Further info
help(mixup)

Installation

pip install mixupy

Requires python 3.7 or higher plus pandas and numpy

pip install numpy pandas

Details

The mixup function enlarges training sets using linear interpolations of features and associated labels as described in https://arxiv.org/abs/1710.09412.

Virtual feature-target pairs are produced from randomly drawn feature-target pairs in the training data. The method is straight-forward and data-agnostic. It should result in a reduction of generalisation error.

mixup constructs additional training examples:

x' = λ * x_i + (1 - λ) * x_j, where x_i, x_j are raw input vectors

y' = λ * y_i + (1 - λ) * y_j, where y_i, y_j are one-hot label encodings

(x_i, y_i) and (x_j ,y_j) are two examples drawn at random from the training data, and λ ∈ [0, 1] with λ ∼ Beta(α, α) for α ∈ (0, ∞). The mixup hyper-parameter α controls the strength of interpolation between feature-target pairs.

mixup() parameters

Parameter	Description	Type	Notes
data	Original data	pandas data frame	Required parameter
alpha	Hyperparameter specifying strength of interpolation	numeric	Defaults to 4
concat	Concatenate mixup data with original data	boolean	Defaults to False
batch_size	How many mixup values to produce	integer	Defaults to number of 'data' examples

The 'data' parameter must be a numeric (integers and/or floats) pandas data frame. Non-finite values are not permitted. Categorical variables should be one-hot encoded.

Alpha values must be greater than or equal to zero. Alpha equal to zero specifies no interpolation.

The mixup function returns a pandas data frame containing interpolated values. Optionally, the original values can be concatenated with the new values using the concat = True option.

Mixup with deep learning versus other learning methods

It is worthwhile distinguishing between mixup usage with deep learning and other learning methods. Mixup with deep learning can improve generalisation when a new mixed dataset is generated every epoch or even better for every minibatch. This level of granularity may not be possible with other learning methods. For example, simple linear modeling may not benefit much from training on a single (potentially greatly expanded) pre-mixed dataset. This single pre-mixed dataset approach is sometimes referred to as 'input mixup'.

In certain situations, under-fitting can occur when conflicts between synthetic labels of the mixup examples and labels of the original training data are present. Some learning methods may be more prone to this under-fitting than others.

Data augmentation as regularisation

Data augmentation is occasionally referred to as a regularisation technique. Regularisation decreases a model's variance by adding prior knowledge (sometimes using shrinkage). Increasing training data (using augmentation) also decreases a model's variance. Data augmentation is also a form of adding prior knowledge to a model.

Citing

If you use mixup in a scientific publication, then consider citing the original paper:

mixup: Beyond Empirical Risk Minimization

By Hongyi Zhang, Moustapha Cisse, Yann N. Dauphin, David Lopez-Paz

https://arxiv.org/abs/1710.09412

I have no affiliation with MIT, FAIR or any of the authors.

Roadmap

• Improve docs
  • Add before and after mixup plots for iris data
  • Add more detailed examples
    • Different data types e.g. image, temporal etc
    • Different parameters
• Add my time series mixup variant
  • Applies mixup technique to two time series separated by 'time_diff' period
  • Implemented and tested in this encoder decoder Jupyter notebook
• Add label preserving option
• Add support for mixing within the same class
  • Usually doesn't perform as well as mixing within all classes
  • May still have some utility e.g. unbalanced data sets

Alternatives

Other implementations:

• pytorch from hongyi-zhang
• pytorch from facebookresearch
• keras from yu4u
• mxnet from unsky
• An R package inspired by 'mixup: Beyond Empirical Risk Minimization'

See Also

Discussion:

• inference.vc
• Openreview

Closely related research:

• Manifold Mixup: Better Representations by Interpolating Hidden States
• MixUp as Locally Linear Out-Of-Manifold Regularization

Loosely related research:

• Label smoothing
• Dropout

Contributing

Pull requests are welcome. For major changes, please open an issue first to discuss what you would like to change.

License

GPL-3