# HashDiff

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HashDiff is a ruby library to compute the smallest difference between two hashes.

**Demo**: [HashDiff](http://hashdiff.herokuapp.com/)

**Docs**: [Documentation](http://rubydoc.info/gems/hashdiff)

## Why HashDiff?

Given two Hashes A and B, sometimes you face the question: what's the smallest changes that can be made to change A to B?

An algorithm responds to this question has to do following:

* Generate a list of additions, deletions and changes, so that `A + ChangeSet = B` and `B - ChangeSet = A`.
* Compute recursively -- Arrays and Hashes may be nested arbitrarily in A or B.
* Compute the smallest change -- it should recoganize similar child Hashes or child Arrays between A and B.

HashDiff answers the question above in an opinionated approach:

* Hash can be represented as a list of (dot-syntax-path, value) pairs. For example, `{a:[{c:2}]}` can be represented as `["a[0].c", 2]`.
* The change set can be represented using the do-syntax representation. For example, `[['-', 'b.x', 3], ['~', 'b.z', 45, 30], ['+', 'b.y', 3]]`.
* It compares Arrays using LCS(longest common subsequence) algorithm.
* It recoganize similar Hashes in Array using a similarity value(0 < similarity <= 1).

## Compatibility

HashDiff is tested against `1.9.2`, `1.9.3` and `ruby-head`. It should work on other versions as well.

## Usage

If you're using bundler, add following to the Gemfile:

    gem 'hashdiff'

Or, you can run `gem install hashdiff`, then add following line to your ruby file which uses HashDiff:

    require 'hashdiff'

## Quick Start

### Diff

Two simple hash:

    a = {a:3, b:2}
    b = {}

    diff = HashDiff.diff(a, b)
    diff.should == [['-', 'a', 3], ['-', 'b', 2]]

More complex hash:

    a = {a:{x:2, y:3, z:4}, b:{x:3, z:45}}
    b = {a:{y:3}, b:{y:3, z:30}}

    diff = HashDiff.diff(a, b)
    diff.should == [['-', 'a.x', 2], ['-', 'a.z', 4], ['-', 'b.x', 3], ['~', 'b.z', 45, 30], ['+', 'b.y', 3]]

Array in hash:

    a = {a:[{x:2, y:3, z:4}, {x:11, y:22, z:33}], b:{x:3, z:45}}
    b = {a:[{y:3}, {x:11, z:33}], b:{y:22}}

    diff = HashDiff.best_diff(a, b)
    diff.should == [['-', 'a[0].x', 2], ['-', 'a[0].z', 4], ['-', 'a[1].y', 22], ['-', 'b.x', 3], ['-', 'b.z', 45], ['+', 'b.y', 22]]

### Patch

patch example:

    a = {a: 3}
    b = {a: {a1: 1, a2: 2}}

    diff = HashDiff.diff(a, b)
    HashDiff.patch!(a, diff).should == b

unpatch example:

    a = [{a: 1, b: 2, c: 3, d: 4, e: 5}, {x: 5, y: 6, z: 3}, 1]
    b = [1, {a: 1, b: 2, c: 3, e: 5}]

    diff = HashDiff.diff(a, b) # diff two array is OK
    HashDiff.unpatch!(b, diff).should == a

## Contributors

- @liufengyun
- @m-o-e

## License

HashDiff is distributed under the MIT-LICENSE.