private Prefix PickRandomKey(MarkovTable frequencies)
{
var candidates = frequencies.Keys
.Where(key => char.IsUpper(key.Elements[0][0]))
.ToList();
int startIndex = RandomInt(0, candidates.Count);
Prefix current = candidates.ElementAt(startIndex);
return(current);
}
/// <summary>
/// Given a <see cref="MarkovTable"/> and an initial starting <see cref="Prefix"/>, looks up the
/// prefix in the MarkovTable to construct a new prefix. This process continues until we reach
/// the end of the original tokens (if ever!).
/// </summary>
private IEnumerable <string> RandomWalk(MarkovTable frequencies, Prefix initial)
{
return(EnumerableEx.Generate(
initialState: initial,
condition: prefix => !prefix.Elements.All(e => e == null),
iterate: prefix =>
{
string suffix = ChooseRandomSuffix(frequencies, prefix);
// slide suffix onto old prefix to create new prefix
var newPrefix = prefix.Elements.Skip(1).Append(suffix).ToArray();
return new Prefix(newPrefix);
},
resultSelector: prefixes => prefixes.Elements.First()
));
}
/// <summary>
/// Create a new markov generator.
/// </summary>
/// <param name="tokens">source sequence of tokens to analyze</param>
/// <param name="ngramSize">
/// The ngram size, i.e. how many consecutive tokens to group by. Larger values
/// result in more similarity to the <paramref name="tokens"/> source.
/// See https://en.wikipedia.org/wiki/N-gram
/// </param>
/// <param name="randomInt">
/// A function that produces a random int between two bounds.
/// If not provided, <see cref="Random.Next(int, int)"/> is used.
/// This parameter is intended to be used mostly in unit testing.
/// </param>
public MarkovGenerator(IReadOnlyCollection <string> tokens, int ngramSize, Func <int, int, int> randomInt = null)
{
frequencies = BuildMarkovTable(tokens, ngramSize);
RandomInt = randomInt ?? new Random().Next;
}
/// <summary>
/// Look up the possible suffixes in <paramref name="frequencies"/> for the <paramref name="current"/> prefix.
/// Each suffix has a weight -- randomly choose one based on the weighting.
/// </summary>
/// <returns>a randomly chosen string suffix</returns>
private string ChooseRandomSuffix(MarkovTable frequencies, Prefix current)
{
if (!frequencies.TryGetValue(current, out SuffixFrequency[] nextFrequencies))
void Add(CompositionCategory category)
{
table = new MarkovTable<Note>(ORDER);
foreach (var c in category.Compositions)
{
if (c.Tracks.Count < 2)
continue;
var mainSeq = NormalizeSequence((c.Tracks[0].GetMainSequence() as MelodySequence));
for (int i = 1; i < c.Tracks.Count; i++)
{
var accompSeq = NormalizeSequence(c.Tracks[i].GetMainSequence() as MelodySequence);
if (accompSeq.TotalRestDuration() > accompSeq.TotalNoteDuration())
continue;
Console.WriteLine("Adding comp {0}:{1}", c.NameTag,i);
table.Add(mainSeq.ToArray(), accompSeq.ToArray());
// Console.WriteLine("Adding track");
}
}
}
