has 0.0.4
Hash array snapshot
License: Apache

# Hash Array Snapshot
## Overview
This project provides a solution to the following two problems:
1. Dataset revisions are seldom tracked effectively but can be just as important to track as source code revisions
2. Version control systems such as Git do not handle large files (i.e. > 1GB) efficiently and struggle to track revisions of large datasets

Hash array snapshots solve these two problems because they are easily tracked by Git and provide a record of the data files associated with a specific source code revision.

## Examples
Suppose we have a dataset composed of images stored in folders.

    -dataset
        -square
            square0.png
            square1.png
            square2.png
        -triangle
            triangle0.png
            triangle1.png
            triangle2.png

*$ has snap -d dataset*

Will create *snapshot.has* with the following contents:

34dc214a2aea8d7c254a9d6dc351e0d3c0088ad998eed6053b78877785fcdff1:triangle/triangle0.png
566f5fa0703f5c2877c38fb3aae0fabbc5f9cdb25499b4f03ca75a6eb3827961:square/square0.png
67240c2cee6e9c77df1192890b1cf4deb265a5a6afdb4a5ecc03e93cc5889cef:triangle/triangle2.png
dfb6352f5d42793b58ac74f2cacf5f1f82bdb1470a30941224a0f1e34766aeb4:square/square2.png
e361db7913f495dafee06657ea67043a49c06fa1a3c57d3ed5b1a9048455de8f:square/square1.png
f7994454bf5a880c5741b3af8e0ababf77f8c450fe47ed8b5c6f7b9d38c9115f:triangle/triangle1.png

Sometime later, additional circle data is added to our dataset and the overall naming convention is changed.

    -dataset
        -square
            square_a.png
            square_b.png
            square_c.png
        -triangle
            triangle_a.png
            triangle_b.png
            triangle_c.png
        -circle
            circle_a.png
            circle_b.png
            circle_c.png

We can use *has check* to verify the dataset is different from what we recorded in our snapshot.

*$ has check -d dataset*

Files added/modified:  
181210f8f9c779c26da1d9b2075bde0127302ee0e3fca38c9a83f5b1dd8e5d3b:circle/circle_c.png
61b4c705859f4158d38090c1e38e8fdc4f3d29db007f012766276aa498835cf6:circle/circle_a.png
e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855:circle/circle_b.png

Even though the triangle and square images have been renamed, files are tracked according to hash value rather than filename so those files are not seen as being new.

We can use our snapshot file *snapshot.has* to recover the older version of our dataset into an empty directory *tmp*.

*$ has recover -b dataset -d tmp*

    -tmp
        -square
            square0.png
            square1.png
            square2.png
        -triangle
            triangle0.png
            triangle1.png
            triangle2.png

Folder *tmp* is now identical to our previous version of folder *dataset*.

We can check the contents of *tmp* to ensure that all files have been copied successfully.

*$ has check -d tmp*

## Installation
The easiest way to install *has* is with *pip install has*.

Alternatively, checkout the latest release version of *has* (e.g. *git checkout v0.0.x*), and run *sudo ./install.sh*. Open a terminal and type *has --help* to verify installation. Uninstall *has* by running *sudo ./uninstall.sh*.