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https://github.com/onmyway133/DeepDiff

🦀Amazingly incredible extraordinary lightning fast diffing in Swift
https://github.com/onmyway133/DeepDiff

batch changes collection diff update

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🦀Amazingly incredible extraordinary lightning fast diffing in Swift

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README 

        
# DeepDiff



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[![CI Status](https://img.shields.io/circleci/project/github/onmyway133/DeepDiff.svg)](https://circleci.com/gh/onmyway133/DeepDiff)

[![Version](https://img.shields.io/cocoapods/v/DeepDiff.svg?style=flat)](http://cocoadocs.org/docsets/DeepDiff)

[![Carthage Compatible](https://img.shields.io/badge/Carthage-compatible-4BC51D.svg?style=flat)](https://github.com/Carthage/Carthage)

[![License](https://img.shields.io/cocoapods/l/DeepDiff.svg?style=flat)](http://cocoadocs.org/docsets/DeepDiff)

[![Platform](https://img.shields.io/cocoapods/p/DeepDiff.svg?style=flat)](http://cocoadocs.org/docsets/DeepDiff)

![Swift](https://img.shields.io/badge/%20in-swift%204.0-orange.svg)



![](Screenshots/Banner.png)



**DeepDiff** tells the difference between 2 collections and the changes as edit steps. It also supports [Texture](https://github.com/TextureGroup/Texture), see [Texture example](https://github.com/onmyway133/DeepDiff/tree/master/Example/DeepDiffTexture)



- Read more [A better way to update UICollectionView data in Swift with diff framework](https://medium.com/flawless-app-stories/a-better-way-to-update-uicollectionview-data-in-swift-with-diff-framework-924db158db86)

- Checkout [Micro](https://github.com/onmyway133/Micro) Fast diffing and type safe SwiftUI style data source for UICollectionView












## Usage



### Basic



The result of `diff` is an array of changes, which is `[Change]`. A `Change` can be



- `.insert`: The item was inserted at an index

- `.delete`: The item was deleted from an index

- `.replace`: The item at this index was replaced by another item

- `.move`: The same item has moved from this index to another index



By default, there is no `.move`. But since `.move` is just `.delete` followed by `.insert` of the same item, it can be reduced by specifying `reduceMove` to `true`.



Here are some examples



```swift

let old = Array("abc")

let new = Array("bcd")

let changes = diff(old: old, new: new)



// Delete "a" at index 0

// Insert "d" at index 2

```



```swift

let old = Array("abcd")

let new = Array("adbc")

let changes = diff(old: old, new: new)



// Move "d" from index 3 to index 1

```



```swift

let old = [

  User(id: 1, name: "Captain America"),

  User(id: 2, name: "Captain Marvel"),

  User(id: 3, name: "Thor"),

]



let new = [

  User(id: 1, name: "Captain America"),

  User(id: 2, name: "The Binary"),

  User(id: 3, name: "Thor"),

]



let changes = diff(old: old, new: new)



// Replace user "Captain Marvel" with user "The Binary" at index 1

```



### DiffAware protocol



Model must conform to `DiffAware` protocol for DeepDiff to work. An model needs to be uniquely identified via `diffId` to tell if there have been any insertions or deletions. In case of same `diffId`, `compareContent` is used to check if any properties have changed, this is for replacement changes. 



```swift

public protocol DiffAware {

  associatedtype DiffId: Hashable



  var diffId: DiffId { get }

  static func compareContent(_ a: Self, _ b: Self) -> Bool

}

```



Some primitive types like `String`, `Int`, `Character` already conform to `DiffAware`



### Animate UITableView and UICollectionView



Changes to `DataSource` can be animated by using batch update, as guided in [Batch Insertion, Deletion, and Reloading of Rows and Sections](https://developer.apple.com/library/content/documentation/UserExperience/Conceptual/TableView_iPhone/ManageInsertDeleteRow/ManageInsertDeleteRow.html#//apple_ref/doc/uid/TP40007451-CH10-SW9)



Since `Change` returned by `DeepDiff` follows the way batch update works, animating `DataSource` changes is easy.



For safety, update your data source model inside `updateData` to ensure synchrony inside `performBatchUpdates`



```swift

let oldItems = items

let newItems = DataSet.generateNewItems()

let changes = diff(old: oldItems, new: newItems)



collectionView.reload(changes: changes, section: 2, updateData: { 

  self.items = newItems

})

```



Take a look at [Demo](https://github.com/onmyway133/DeepDiff/tree/master/Example/DeepDiffDemo) where changes are made via random number of items, and the items are shuffled.



## How does it work



### [Wagner–Fischer](https://en.wikipedia.org/wiki/Wagner%E2%80%93Fischer_algorithm)



If you recall from school, there is [Levenshtein distance](https://en.wikipedia.org/wiki/Levenshtein_distance) which counts the minimum edit distance to go from one string to another.



Based on that, the first version of `DeepDiff` implements Wagner–Fischer, which uses [dynamic programming](https://en.wikipedia.org/wiki/Dynamic_programming) to compute the edit steps between 2 strings of characters. `DeepDiff` generalizes this to make it work for any collection.



Some optimisations made



- Check empty old or new collection to return early

- Use `diffId` to quickly check that 2 items are not equal

- Follow "We can adapt the algorithm to use less space, O(m) instead of O(mn), since it only requires that the previous row and current row be stored at any one time." to use 2 rows, instead of matrix to reduce memory storage.



The performance greatly depends on the number of items, the changes and the complexity of the `equal` function.



`Wagner–Fischer algorithm` has O(mn) complexity, so it should be used for collection with < 100 items.



### Heckel



The current version of `DeepDiff` uses Heckel algorithm as described in [A technique for isolating differences between files](https://dl.acm.org/citation.cfm?id=359467). It works on 2 observations about line occurrences and counters. The result is a bit lengthy compared to the first version, but it runs in linear time.



Thanks to



- [Isolating Differences Between Files](https://gist.github.com/ndarville/3166060) for explaining step by step

- [HeckelDiff](https://github.com/mcudich/HeckelDiff) for a clever move reducer based on tracking `deleteOffset`



### More



There are other algorithms that are interesting



- [An O(ND) Difference Algorithm and Its Variations](http://www.xmailserver.org/diff2.pdf)

- [An O(NP) Sequence Comparison Algorithm](https://publications.mpi-cbg.de/Wu_1990_6334.pdf)



## Benchmarks



Benchmarking is done on real device iPhone 6, with random items made of UUID strings (36 characters including hyphens), just to make comparisons more difficult.



You can take a look at the code [Benchmark](https://github.com/onmyway133/DeepDiff/tree/master/Example/Benchmark). Test is inspired from [DiffUtil](https://developer.android.com/reference/android/support/v7/util/DiffUtil.html)



### Among different frameworks



Here are several popular diffing frameworks to compare



- [Differ](https://github.com/tonyarnold/Differ) 1.0.3, originally [Diff.swift](https://github.com/wokalski/Diff.swift)

- [Changeset](https://github.com/osteslag/Changeset) 3.0

- [Dwifft](https://github.com/jflinter/Dwifft) 0.8

- [ListDiff](https://github.com/lxcid/ListDiff) 0.1.0, port from [IGListKit](https://github.com/Instagram/IGListKit/)



💪 From 2000 items to 2100 items (100 deletions, 200 insertions)



```swift

let (old, new) = generate(count: 2000, removeRange: 100..<200, addRange: 1000..<1200)



benchmark(name: "DeepDiff", closure: {

  _ = DeepDiff.diff(old: old, new: new)

})



benchmark(name: "Dwifft", closure: {

  _ = Dwifft.diff(old, new)

})



benchmark(name: "Changeset", closure: {

  _ = Changeset.edits(from: old, to: new)

})



benchmark(name: "Differ", closure: {

  _ = old.diffTraces(to: new)

})



benchmark(name: "ListDiff", closure: {

  _ = ListDiff.List.diffing(oldArray: old, newArray: new)

})

```



**Result**



```

DeepDiff: 0.0450611114501953s

Differ: 0.199673891067505s

Dwifft: 149.603884935379s

Changeset: 77.5895738601685s

ListDiff: 0.105544805526733s

```



![](Screenshots/benchmark3d.png)



### Increasing complexity



Here is how `DeepDiff` handles large number of items and changes



💪 From 10000 items to 11000 items (1000 deletions, 2000 insertions)



```

DeepDiff: 0.233131170272827s

```



💪 From 20000 items to 22000 items (2000 deletions, 4000 insertions)



```

DeepDiff: 0.453393936157227s

```



💪 From 50000 items to 55000 items (5000 deletions, 10000 insertions)



```

DeepDiff: 1.04128122329712s

```



💪 From 100000 items to 1000000 items



```

Are you sure?

```



## Installation



### CocoaPods



Add the following to your Podfile



```ruby

pod 'DeepDiff'

```



### Carthage



Add the following to your Cartfile



```ruby

github "onmyway133/DeepDiff"

```



### Swift Package Manager

Add the following to your Package.swift file



```swift

.package(url: "https://github.com/onmyway133/DeepDiff.git", .upToNextMajor(from: "2.3.0"))

```



**DeepDiff** can also be installed manually. Just download and drop `Sources` folders in your project.



## Author



Khoa Pham, [email protected]



## Contributing



We would love you to contribute to **DeepDiff**, check the [CONTRIBUTING](https://github.com/onmyway133/DeepDiff/blob/master/CONTRIBUTING.md) file for more info.



## License



**DeepDiff** is available under the MIT license. See the [LICENSE](https://github.com/onmyway133/DeepDiff/blob/master/LICENSE.md) file for more info.