Observations

Observations provides a one line Python API for loading standard data sets in machine learning. It automates the process from downloading, extracting, loading, and preprocessing data. Observations helps keep the workflow reproducible and follow sensible standards.

It can be used in two ways.

1. As a package

Install it.

pip install observations

Import it.

from observations import svhn

(x_train, y_train), (x_test, y_test) = svhn("~/data")

All functions take as input a filepath and optional preprocessing arguments. They return a tuple in the form of training data, test data, and validation data (if available). Each element in the tuple is typically a NumPy array, a tuple of NumPy arrays (e.g., features and labels), or a string (text). See the API for details.

2. As source code

Copy and paste functions inside the codebase relevant for your experiments.

def enwik8(path):
  ...

x_train, x_test, x_valid = enwik8("~/data")

Each function has minimal dependencies. For example, enwik8.py only depends on core libraries and the external function maybe_download_and_extract in util.py. The functions are designed to be easy to read and hack at.

FAQ

Which approach should I take?

It depends on your use case.

As a package, dozens of data sets are at your disposal. The package establishes sensible standards for conveniently loading in data and thus quickly experimenting with them.
As source code, you have complete flexibility—from the initial download all the way to preprocessing the data as NumPy arrays.

How do I use minibatches of data?

The data loading functions return the full data. It's up to your needs to generate batches.

One helpful utility is

def generator(array, batch_size):
  """Generate batch with respect to array's first axis."""
  start = 0  # pointer to where we are in iteration
  while True:
    stop = start + batch_size
    diff = stop - array.shape[0]
    if diff <= 0:
      batch = array[start:stop]
      start += batch_size
    else:
      batch = np.concatenate((array[start:], array[:diff]))
      start = diff
    yield batch

To use it, simply write

from observations import cifar10
(x_train, y_train), (x_test, y_test) = cifar10("~/data")
x_train_data = generator(x_train, 256)

for batch in x_train_data:
  ...  # operate on batch

batch = next(x_train_data)  # alternatively, increment the iterator

There's also an extended version. It takes a list of arrays as input and yields a list of batches.

def generator(arrays, batch_size):
  """Generate batches, one with respect to each array's first axis."""
  starts = [0] * len(arrays)  # pointers to where we are in iteration
  while True:
    batches = []
    for i, array in enumerate(arrays):
      start = starts[i]
      stop = start + batch_size
      diff = stop - array.shape[0]
      if diff <= 0:
        batch = array[start:stop]
        starts[i] += batch_size
      else:
        batch = np.concatenate((array[start:], array[:diff]))
        starts[i] = diff
      batches.append(batch)
    yield batches

To use it, simply write

from observations import cifar10
(x_train, y_train), (x_test, y_test) = cifar10("~/data")
train_data = generator([x_train, y_train], 256)

for x_batch, y_batch in train_data:
  ...  # operate on batch

x_batch, y_batch = next(train_data)  # alternatively, increment the iterator

Contributing

We'd like your help! Any pull requests which help maintain the existing functions and/or add new ones are appreciated. We follow Edward's standards for style and documentation.

Each function takes as input a filepath and optional preprocessing arguments. All necessary packages that aren't from the Python Standard Library, NumPy, or six are imported inside the function's body. The functions proceed as follows:

Check if the extracted file(s) exist in the filepath. If it does, skip to step 4.
Check if the compressed file(s) exist in the filepath. If it doesn't, download it.
Extract the compressed file(s).
Load the data into memory.
- For data sets larger than 1 GB, the function will terminate with a message advising to load the files as batches.
Preprocess the data.
Return a tuple in the form of training data, test data, and validation data (if available). Each element in the tuple is typically a NumPy array, a tuple of NumPy arrays (e.g., features and labels), or a string (text).