public BoundMapper(IExceptionContext ectx, TreeEnsembleFeaturizerBindableMapper owner,
RoleMappedSchema schema)
{
Contracts.AssertValue(ectx);
ectx.AssertValue(owner);
ectx.AssertValue(schema);
ectx.Assert(schema.Feature.HasValue);
_ectx = ectx;
_owner = owner;
InputRoleMappedSchema = schema;
// A vector containing the output of each tree on a given example.
var treeValueType = new VectorType(NumberType.Float, owner._ensemble.TrainedEnsemble.NumTrees);
// An indicator vector with length = the total number of leaves in the ensemble, indicating which leaf the example
// ends up in all the trees in the ensemble.
var leafIdType = new VectorType(NumberType.Float, owner._totalLeafCount);
// An indicator vector with length = the total number of nodes in the ensemble, indicating the nodes on
// the paths of the example in all the trees in the ensemble.
// The total number of nodes in a binary tree is equal to the number of internal nodes + the number of leaf nodes,
// and it is also equal to the number of children of internal nodes (which is 2 * the number of internal nodes)
// plus one (since the root node is not a child of any node). So we have #internal + #leaf = 2*(#internal) + 1,
// which means that #internal = #leaf - 1.
// Therefore, the number of internal nodes in the ensemble is #leaf - #trees.
var pathIdType = new VectorType(NumberType.Float, owner._totalLeafCount - owner._ensemble.TrainedEnsemble.NumTrees);
// Start creating output schema with types derived above.
var schemaBuilder = new SchemaBuilder();
// Metadata of tree values.
var treeIdMetadataBuilder = new MetadataBuilder();
treeIdMetadataBuilder.Add(MetadataUtils.Kinds.SlotNames, MetadataUtils.GetNamesType(treeValueType.Size),
(ValueGetter <VBuffer <ReadOnlyMemory <char> > >)owner.GetTreeSlotNames);
// Add the column of trees' output values
schemaBuilder.AddColumn(OutputColumnNames.Trees, treeValueType, treeIdMetadataBuilder.GetMetadata());
// Metadata of leaf IDs.
var leafIdMetadataBuilder = new MetadataBuilder();
leafIdMetadataBuilder.Add(MetadataUtils.Kinds.SlotNames, MetadataUtils.GetNamesType(leafIdType.Size),
(ValueGetter <VBuffer <ReadOnlyMemory <char> > >)owner.GetLeafSlotNames);
leafIdMetadataBuilder.Add(MetadataUtils.Kinds.IsNormalized, BoolType.Instance, (ref bool value) => value = true);
// Add the column of leaves' IDs where the input example reaches.
schemaBuilder.AddColumn(OutputColumnNames.Leaves, leafIdType, leafIdMetadataBuilder.GetMetadata());
// Metadata of path IDs.
var pathIdMetadataBuilder = new MetadataBuilder();
pathIdMetadataBuilder.Add(MetadataUtils.Kinds.SlotNames, MetadataUtils.GetNamesType(pathIdType.Size),
(ValueGetter <VBuffer <ReadOnlyMemory <char> > >)owner.GetPathSlotNames);
pathIdMetadataBuilder.Add(MetadataUtils.Kinds.IsNormalized, BoolType.Instance, (ref bool value) => value = true);
// Add the column of encoded paths which the input example passes.
schemaBuilder.AddColumn(OutputColumnNames.Paths, pathIdType, pathIdMetadataBuilder.GetMetadata());
OutputSchema = schemaBuilder.GetSchema();
// Tree values must be the first output column.
Contracts.Assert(OutputSchema[OutputColumnNames.Trees].Index == TreeValuesColumnId);
// leaf IDs must be the second output column.
Contracts.Assert(OutputSchema[OutputColumnNames.Leaves].Index == LeafIdsColumnId);
// Path IDs must be the third output column.
Contracts.Assert(OutputSchema[OutputColumnNames.Paths].Index == PathIdsColumnId);
}