split-data-loader

This package contains simple utility functions related to writing and reading data (typically related to machine learning) using multiple files.

There are mainly two extremes when dealing with data.

1. All the data in a single file - This is good for sequential access, but can be cumbersome to shuffle data when reading.
2. Each frame in its own file - This creates too many tiny files and can be difficult to scale.

This library uses an intermediate approach. The entire dataset is split and stored in multiple files (eg: N = 128) called bins. It allows easy shuffling of data and parallel processing when required.

This library also uses an index file to keep track of the order and location of each packet. It allows index based random lookup of all the input packets, distributed among all the bin files.

Note

The "split" here has nothing to do with train/test split. It is expected that train/test split is done before writing data using the methods given here.

Installation

Use pip. The project is available at PyPI.

pip install splitdataloader

Writing Data

Use write_split_data to write data to a target directory.

from splitdataloader import write_split_data

def example_writer(...):
    # Get the data source
    data_source: Iterable[bytes] = some_source()
    target_dir = "tmp/training_data"
    write_split_data(target_dir, data_source, splits=128)

During writing, data will be distributed among all the bins.

The function write_split_data is defined as follows.

def write_split_data(
    target_dir: str,
    input_sequence: Iterable[bytes],
    splits: int = 256,
    shuffle: bool = False,
    start_clean: bool = False,
) -> None:
    ...

• target_dir - this is the directory where all bin files and index file will be stored
• input_sequence - input data source (corresponding to a single frame, not batch)
• splits - number of splits to use
• shuffle - if true, shuffle the order of bins when writing each frame
• start_clean - if true, clear the contents of the target_dir before start. Otherwise, new frames will be appended to the existing bins.

Reading Data

This is the main objective of this library. The class SplitDataLoader handles the loading of data. It supports the following:

1. Getting length using len()
2. Random indexing using []
3. Data iteration (binwise), with support for shuffling

from splitdataloader import SplitDataLoader

def example_loader(...):
    # Get the data source
    data_dir = "tmp/training_data"
    loader = SplitDataLoader(data_dir)
    # Supports len()
    print(len(loader))
    # Supports indexing
    data  = loader[2]
    # Supports iteration
    for data in loader.iterate_binwise(shuffle=True):
        do_something(data)

Here the method iterate_binwise is useful for shuffling data during the loading. If shuffle is False, frames will be iterated in the same order they appear in the bins.

Multiprocessing Queue Based Iterator

If the loading takes too much time, it is probably a good idea to run the loading part in a separate process. If it is possible to refactor the entity that produces the batches as a generator, splitdataloader.MpQItr can be used to handle loading. Data will be loaded to an internal queue while it is being processed in the main process.

from splitdataloader import MpQItr

# A tuple, class, or whatever that handles the batch
class BatchType:
    ...

# A generator function that produces the batches
def batch_generator(...) -> Iterator[BatchType]:
    ...

def batch_wise_processing(...):
    # Multi-processing queue based iterator
    queued_batch_iterator = MpQItr[BatchType](
        batch_generator,  # the generator function
        args... # args or kwargs to the generator function
    )
    for batch in queued_batch_iterator:
        do_something_with(batch)

In the above, the batch_generator function should be provided by the user. It should do the following:

1. load the data
2. pre-process (scaling, normalization, etc)
3. combine multiple frames into batches
4. yield the batch

This will make sure that all the pre-processing is handled by a separate process and the main process only has to deal with the model training (or validation).