NParallelTextCorpus (#270)

* Working NParallelTextCorpus
* Change mergedtextcorpus parameter
* Move same ref rows out of range info
* Make seed optional; remove unneeded code

src/SIL.Machine/Corpora/CorporaExtensions.cs

@@ -523,6 +523,33 @@ public override IEnumerable<TextRow> GetRows(IEnumerable<string> textIds)
 
         #endregion
 
+        #region INParallelTextCorpus operations
+
+        public static INParallelTextCorpus AlignMany(
+            this IEnumerable<ITextCorpus> corpora,
+            IEnumerable<bool> allRowsPerCorpus = null
+        )
+        {
+            NParallelTextCorpus nParallelTextCorpus = new NParallelTextCorpus(corpora);
+            if (allRowsPerCorpus != null)
+            {
+                nParallelTextCorpus.AllRows = allRowsPerCorpus.ToArray();
+            }
+            return nParallelTextCorpus;
+        }
+
+        public static ITextCorpus ChooseRandom(this IEnumerable<ITextCorpus> corpora, int? seed = null)
+        {
+            return new MergedTextCorpus(corpora, MergeRule.Random, seed);
+        }
+
+        public static ITextCorpus ChooseFirst(this IEnumerable<ITextCorpus> corpora)
+        {
+            return new MergedTextCorpus(corpora, MergeRule.First);
+        }
+
+        #endregion
+
         #region IAlignmentCorpus operations
 
         public static IAlignmentCorpus Transform(

src/SIL.Machine/Corpora/CorpusAlignmentException.cs

@@ -8,5 +8,10 @@ public CorpusAlignmentException(string sourceRef, string targetRef)
             : base(
                 $"Invalid format in {sourceRef} and {targetRef}. Mismatched key formats \"{sourceRef}\" and \"{targetRef}\". There may be an extraneous tab, missing ref, or inconsistent use of user-defined refs."
             ) { }
+
+        public CorpusAlignmentException(string[] refs)
+            : base(
+                $"Invalid format in {string.Join(", ", refs)}. Mismatched key formats. There may be an extraneous tab, missing ref, or inconsistent use of user-defined refs."
+            ) { }
     }
 }

src/SIL.Machine/Corpora/INParallelTextCorpus.cs

@@ -0,0 +1,11 @@
+using System.Collections.Generic;
+
+namespace SIL.Machine.Corpora
+{
+    public interface INParallelTextCorpus : ICorpus<NParallelTextRow>
+    {
+        int Count(bool includeEmpty = true, IEnumerable<string> textIds = null);
+
+        IEnumerable<NParallelTextRow> GetRows(IEnumerable<string> textIds);
+    }
+}

src/SIL.Machine/Corpora/MergeRule.cs

@@ -0,0 +1,8 @@
+namespace SIL.Machine.Corpora
+{
+    public enum MergeRule
+    {
+        First,
+        Random
+    }
+}

src/SIL.Machine/Corpora/MergedTextCorpus.cs

@@ -0,0 +1,77 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using SIL.Scripture;
+
+namespace SIL.Machine.Corpora
+{
+    public class MergedTextCorpus : TextCorpusBase
+    {
+        private readonly NParallelTextCorpus _corpus;
+
+        private readonly MergeRule _mergeRule;
+
+        private readonly Random _random;
+
+        public MergedTextCorpus(IEnumerable<ITextCorpus> corpora, MergeRule mergeRule, int? seed = null)
+        {
+            _corpus = new NParallelTextCorpus(corpora) { AllRows = Enumerable.Repeat(true, corpora.Count()).ToArray() };
+            _mergeRule = mergeRule;
+            if (seed != null)
+                _random = new Random(seed.Value);
+            else
+                _random = new Random();
+        }
+
+        public override IEnumerable<IText> Texts => _corpus.Corpora.SelectMany(c => c.Texts);
+
+        public override bool IsTokenized => Enumerable.Range(0, _corpus.N).All(i => _corpus.IsTokenized(i));
+
+        public override ScrVers Versification => _corpus.N > 0 ? _corpus.Corpora[0].Versification : null;
+
+        public override IEnumerable<TextRow> GetRows(IEnumerable<string> textIds)
+        {
+            int indexOfInRangeRow = -1;
+            foreach (NParallelTextRow nRow in _corpus.GetRows(textIds))
+            {
+                IReadOnlyList<int> nonEmptyIndices = nRow
+                    .NSegments.Select((s, i) => (s, i))
+                    .Where(pair => pair.s.Count > 0 || nRow.IsInRange(pair.i))
+                    .Select(pair => pair.i)
+                    .ToList();
+                IReadOnlyList<int> indices =
+                    nonEmptyIndices.Count > 0 ? nonEmptyIndices : Enumerable.Range(0, nRow.N).ToList();
+                if (indexOfInRangeRow == -1)
+                {
+                    indices = indices.Where(i => nRow.IsRangeStart(i) || !nRow.IsInRange(i)).ToList();
+                }
+                if (indices.Count == 0)
+                    continue;
+                int indexOfSelectedRow = -1;
+                switch (_mergeRule)
+                {
+                    case MergeRule.First:
+                        indexOfSelectedRow = indices.First();
+                        break;
+                    case MergeRule.Random:
+                        indexOfSelectedRow = indices[_random.Next(0, indices.Count)];
+                        break;
+                }
+                indexOfSelectedRow = indexOfInRangeRow != -1 ? indexOfInRangeRow : indexOfSelectedRow;
+                if (!nRow.IsInRange(indexOfSelectedRow))
+                {
+                    indexOfInRangeRow = -1;
+                }
+                if (nRow.IsRangeStart(indexOfSelectedRow))
+                {
+                    indexOfInRangeRow = indexOfSelectedRow;
+                }
+                yield return new TextRow(nRow.TextId, nRow.Ref)
+                {
+                    Segment = nRow.NSegments[indexOfSelectedRow],
+                    Flags = nRow.NFlags[indexOfSelectedRow]
+                };
+            }
+        }
+    }
+}