LanguageProcessing100knock2015.swift

// 05. n-gram
// 与えられたシーケンス（文字列やリストなど）からn-gramを作る関数を作成せよ．この関数を用い，"I am an NLPer"という文から単語bi-gram，文字bi-gramを得よ．
// 単語bi-gram
func q5_1(input: String, n: Int) -> [String] {
   return wordNgram(input: input, n: n)
}

// 文字bi-gram
func q5_2(input: String, n: Int) -> [String] {
    return charNgram(input: input, n: n)
}

func wordNgram(input: String, n: Int) -> [String] {
    let words = input.components(separatedBy: " ").map{ $0.trimmingCharacters(in: CharacterSet(charactersIn: ",.")) }
    return words.enumerated().flatMap{ (i, v) in
        if words.indices.contains(i + n - 1) {
            return words[i..<i+n].reduce("", +)
        } else {
            return nil
        }
    }
}

func charNgram(input: String, n: Int) -> [String] {
    let words = input.components(separatedBy: " ")
                          .map{ $0.trimmingCharacters(in: CharacterSet(charactersIn: ",.")) }
                          .joined().characters.map{ String($0) }
    return words.enumerated().flatMap{ (i, v) in
        if words.indices.contains(i + n - 1) {
            return words[i..<i+n].reduce("", +)
        } else {
            return nil
        }
    }
}

/// テストコード
func testQ5_1() {
    let actual1 = q5_1(input: "I am an NLPer", n: 2)
    let expected1 = ["Iam", "aman", "anNLPer"]
    XCTAssertEqual(actual1, expected1)

    let actual2 = q5_1(input: "I am a Swifter", n: 2)
    let expected2 = ["Iam", "ama", "aSwifter"]
    XCTAssertEqual(actual2, expected2)

    let actual3 = q5_1(input: "This is a pen, Thease are erasers.", n: 2)
    let expected3 = ["Thisis", "isa", "apen", "penThease", "Theaseare", "areerasers"]
    XCTAssertEqual(actual3, expected3)

    let actual4 = q5_1(input: "I am a Swifter", n: 3)
    let expected4 = ["Iama", "amaSwifter"]
    XCTAssertEqual(actual4, expected4)

    let actual5 = q5_1(input: "This is a pen, Thease are erasers.", n: 4)
    let expected5 = ["Thisisapen", "isapenThease", "apenTheaseare", "penTheaseareerasers"]
    XCTAssertEqual(actual5, expected5)
}

func testQ5_2() {
    let actual1 = q5_2(input: "I am an NLPer", n: 2)
    let expected1 = ["Ia", "am", "ma", "an", "nN", "NL", "LP", "Pe", "er"]
        XCTAssertEqual(actual1, expected1)
    }