/// <summary>
/// Create a <see cref="Dataset"/> for storing training and prediciton data under LightGBM framework. The main goal of this function
/// is not marshaling ML.NET data set into LightGBM format but just creates a (unmanaged) container where examples can be pushed into by calling
/// <see cref="PushRows(float[], int, int, int)"/>. It also pre-allocates memory so the actual size (number of examples and number of features)
/// of the data set is required. A sub-sampled version of the original data set is passed in to compute some statictics needed by the training
/// procedure. Note that we use "original" to indicate a property from the unsampled data set.
/// </summary>
/// <param name="sampleValuePerColumn">A 2-D array which encodes the sub-sampled data matrix. sampleValuePerColumn[i] stores
/// all the non-zero values of the i-th feature. sampleValuePerColumn[i][j] is the j-th non-zero value of i-th feature encountered when scanning
/// the values row-by-row (i.e., example-by-example) in the matrix and column-by-column (i.e., feature-by-feature) within one row. It is similar
/// to CSC format for storing sparse matrix.</param>
/// <param name="sampleIndicesPerColumn">A 2-D array which encodes sub-sampled example indexes of non-zero features stored in sampleValuePerColumn.
/// The sampleIndicesPerColumn[i][j]-th example has a non-zero i-th feature whose value is sampleValuePerColumn[i][j].</param>
/// <param name="numCol">Total number of features in the original data.</param>
/// <param name="sampleNonZeroCntPerColumn">sampleNonZeroCntPerColumn[i] is the size of sampleValuePerColumn[i].</param>
/// <param name="numSampleRow">The number of sampled examples in the sub-sampled data matrix.</param>
/// <param name="numTotalRow">The number of original examples added using <see cref="PushRows(float[], int, int, int)"/>.</param>
/// <param name="param">LightGBM parameter used in https://github.com/Microsoft/LightGBM/blob/c920e6345bcb41fc1ec6ac338f5437034b9f0d38/src/c_api.cpp#L421. </param>
/// <param name="labels">Labels of the original data. labels[i] is the label of the i-th original example.</param>
/// <param name="weights">Example weights of the original data. weights[i] is the weight of the i-th original example.</param>
/// <param name="groups">Group identifiers of the original data. groups[i] is the group ID of the i-th original example.</param>
public unsafe Dataset(double[][] sampleValuePerColumn,
int[][] sampleIndicesPerColumn,
int numCol,
int[] sampleNonZeroCntPerColumn,
int numSampleRow,
int numTotalRow,
string param, float[] labels, float[] weights = null, int[] groups = null)
{
_handle = null;
// Use GCHandle to pin the memory, avoid the memory relocation.
GCHandle[] gcValues = new GCHandle[numCol];
GCHandle[] gcIndices = new GCHandle[numCol];
try
{
double *[] ptrArrayValues = new double *[numCol];
int *[] ptrArrayIndices = new int *[numCol];
for (int i = 0; i < numCol; i++)
{
gcValues[i] = GCHandle.Alloc(sampleValuePerColumn[i], GCHandleType.Pinned);
ptrArrayValues[i] = (double *)gcValues[i].AddrOfPinnedObject().ToPointer();
gcIndices[i] = GCHandle.Alloc(sampleIndicesPerColumn[i], GCHandleType.Pinned);
ptrArrayIndices[i] = (int *)gcIndices[i].AddrOfPinnedObject().ToPointer();
}
;
fixed(double **ptrValues = ptrArrayValues)
fixed(int **ptrIndices = ptrArrayIndices)
{
// Create container. Examples will pushed in later.
LightGbmInterfaceUtils.Check(WrappedLightGbmInterface.DatasetCreateFromSampledColumn(
(IntPtr)ptrValues, (IntPtr)ptrIndices, numCol, sampleNonZeroCntPerColumn, numSampleRow, numTotalRow,
param, out _handle));
}
}
finally
{
for (int i = 0; i < numCol; i++)
{
if (gcValues[i].IsAllocated)
{
gcValues[i].Free();
}
if (gcIndices[i].IsAllocated)
{
gcIndices[i].Free();
}
}
;
}
// Before adding examples (i.e., feature vectors of the original data set), the original labels, weights, and groups are added.
SetLabel(labels);
SetWeights(weights);
SetGroup(groups);
Contracts.Assert(GetNumCols() == numCol);
Contracts.Assert(GetNumRows() == numTotalRow);
}
public Dataset(Dataset reference, int numTotalRow, float[] labels, float[] weights = null, int[] groups = null)
{
WrappedLightGbmInterface.SafeDataSetHandle refHandle = reference?.Handle;
LightGbmInterfaceUtils.Check(WrappedLightGbmInterface.DatasetCreateByReference(refHandle, numTotalRow, out _handle));
SetLabel(labels);
SetWeights(weights);
SetGroup(groups);
}
public void Dispose()
{
_handle?.Dispose();
_handle = null;
}