arr.split(where:)

💾 程式

此方法會交由 where: 參數來判斷：「原陣列中，前後兩元素之間該不該斷開，形成新的子陣列」。

💈範例：

let array = [1, 2, 2, 2, 3, 4, 4]

// ⭐️ equivalent to: `array.split { $0 != $1 }`
array.split(where: !=)    // [[1], [2, 2, 2], [3], [4, 4]]

💾 程式：

// ⭐️ arr.split(where:)
extension Array {
    
    /// split an array into array of subarrays.
    public func split(
        where shouldSplit: (Element, Element) -> Bool
    ) -> [[Element]] 
    { 
        // result of splitting (array of subarrays)
        var result: [[Element]] = isEmpty ? [] : [[self[0]]]
        
        // for each (previous, current) pair
        for (previous, current) in zip(self, self.dropFirst()) { 
            // if should split, 
            if shouldSplit(previous, current) {
                // append new subarray
                // --------------------
                result.append([current])     
            } else {
                // else append to the last subarray.
                // -----------------------------------
                // 🧨 Note: 
                //   don't use `result.last` to append,
                //   the `last` property is immutable❗️ 
                result[result.endIndex-1].append(current)
            }
        } 
        
        return result
    }
}

📗 參考

• objc.io ⟩ Advanced Swift (2019.05), p. 32

• Paul ⟩ How to split an array into chunks

📘 手冊

• Swift Algorithms ⟩ Collection ⟩ chunked(by:) ⭐️

• Swift ⟩

  • Array ⟩

    • split(maxSplits:omittingEmptySubsequences:whereSeparator:)

    • dropFirst(_:) -> ArraySlice<Element> (⭐️ 注意：.dropFirst 並沒有把第一個元素去除❗️)

    • ArraySlice

  • Collection ⟩ .isEmpty

  • Swift Standard Library ⟩ Collections ⟩ zip(_:_:)

🗣 討論

• How to split an array in half in Swift?

👥 相關

• Merge Sort splits arrays in half recursively.

• str.split() splits String into [Substring].

• similar to arr.split(size:).