ArrayでGroupBy

GroupBy.swift

import UIKit

public protocol Groupable {
    func sameGroupAs(other: Self) -> Bool
}

extension CollectionType {
    
    public typealias ItemType = Self.Generator.Element
    public typealias Grouper = (ItemType, ItemType) -> Bool
    
    public func groupBy(grouper: Grouper) -> [[ItemType]] {
        var result: Array<Array<ItemType>> = []
        
        var previousItem: ItemType?
        var group = [ItemType]()
        
        for item in self {
            defer { previousItem = item }
            
            guard let previous = previousItem else {
                group.append(item)
                continue
            }
            
            if grouper(previous, item) {
                group.append(item)
            }
            else {
                result.append(group)
                group = [ItemType]()
                group.append(item)
            }
            
        }
        
        result.append(group)
        
        return result
        
    }
    
}
extension CollectionType where Self.Generator.Element: Groupable {
    
    public func group() -> [[Self.Generator.Element]] {
        return self.groupBy { $0.sameGroupAs($1) }
    }
    
}

extension CollectionType where Self.Generator.Element: Comparable {
    
    public func uniquelyGroupBy(grouper: (Self.Generator.Element, Self.Generator.Element) -> Bool) -> [[Self.Generator.Element]] {
        let sorted = self.sort()
        return sorted.groupBy(grouper)
    }
    
}