Any libraries to convert number Pinyin to Pinyin with tone markings?

Question

Just wondering if anyone knows of a class library that can convert Chinese Pinyin to ones with tones, such as nin2 hao3 ma to nín hǎo ma. It would be similar to this answer

Answer 1

Here is my porting of @Greg-Hewgill python algorithm to C#. I haven't run into any issues so far.

public static string ConvertNumericalPinYinToAccented(string input)
    {
        Dictionary PinyinToneMark = new Dictionary
        {
            {0, "aoeiuv\u00fc"},
            {1, "\u0101\u014d\u0113\u012b\u016b\u01d6\u01d6"},
            {2, "\u00e1\u00f3\u00e9\u00ed\u00fa\u01d8\u01d8"},
            {3, "\u01ce\u01d2\u011b\u01d0\u01d4\u01da\u01da"},
            {4, "\u00e0\u00f2\u00e8\u00ec\u00f9\u01dc\u01dc"}
        };

        string[] words = input.Split(' ');
        string accented = "";
        string t = "";
        foreach (string pinyin in words)
        {
            foreach (char c in pinyin)
            {
                if (c >= 'a' && c <= 'z')
                {
                    t += c;
                }
                else if (c == ':')
                {
                    if (t[t.Length - 1] == 'u')
                    {
                        t = t.Substring(0, t.Length - 2) + "\u00fc";
                    }
                }
                else
                {
                    if (c >= '0' && c <= '5')
                    {
                        int tone = (int)Char.GetNumericValue(c) % 5;

                        if (tone != 0)
                        {
                            Match match = Regex.Match(t, "[aoeiuv\u00fc]+");
                            if (!match.Success)
                            {
                                t += c;
                            }
                            else if (match.Groups[0].Length == 1)
                            {
                                t = t.Substring(0, match.Groups[0].Index) +
                                    PinyinToneMark[tone][PinyinToneMark[0].IndexOf(match.Groups[0].Value[0])]
                                    + t.Substring(match.Groups[0].Index + match.Groups[0].Length);
                            }
                            else
                            {
                                if (t.Contains("a"))
                                {
                                    t = t.Replace("a", PinyinToneMark[tone][0].ToString());
                                }
                                else if (t.Contains("o"))
                                {
                                    t = t.Replace("o", PinyinToneMark[tone][1].ToString());
                                }
                                else if (t.Contains("e"))
                                {
                                    t = t.Replace("e", PinyinToneMark[tone][2].ToString());
                                }
                                else if (t.Contains("ui"))
                                {
                                    t = t.Replace("i", PinyinToneMark[tone][3].ToString());
                                }
                                else if (t.Contains("iu"))
                                {
                                    t = t.Replace("u", PinyinToneMark[tone][4].ToString());
                                }
                                else
                                {
                                    t += "!";
                                }
                            }
                        }
                    }
                    accented += t;
                    t = "";
                }
            }
            accented += t + " ";
        }
        accented = accented.TrimEnd();
        return accented;
    }