/// <summary>
/// Returns the feature selection scores for each slot of each column.
/// </summary>
/// <param name="env">The host environment.</param>
/// <param name="input">The input dataview.</param>
/// <param name="columns">The columns for which to compute the feature selection scores.</param>
/// <param name="colSizes">Outputs an array containing the vector sizes of the input columns</param>
/// <returns>A list of scores.</returns>
public static long[][] Train(IHostEnvironment env, IDataView input, string[] columns, out int[] colSizes)
{
Contracts.CheckValue(env, nameof(env));
env.CheckValue(input, nameof(input));
env.CheckParam(Utils.Size(columns) > 0, nameof(columns));
var schema = input.Schema;
var size = columns.Length;
var activeInput = new bool[schema.ColumnCount];
var colSrcs = new int[size];
var colTypes = new ColumnType[size];
colSizes = new int[size];
for (int i = 0; i < size; i++)
{
int colSrc;
var colName = columns[i];
if (!schema.TryGetColumnIndex(colName, out colSrc))
{
throw env.ExceptUserArg(nameof(CountFeatureSelectionTransform.Arguments.Column), "Source column '{0}' not found", colName);
}
var colType = schema.GetColumnType(colSrc);
if (colType.IsVector && !colType.IsKnownSizeVector)
{
throw env.ExceptUserArg(nameof(CountFeatureSelectionTransform.Arguments.Column), "Variable length column '{0}' is not allowed", colName);
}
activeInput[colSrc] = true;
colSrcs[i] = colSrc;
colTypes[i] = colType;
colSizes[i] = colType.ValueCount;
}
var aggregators = new CountAggregator[size];
long rowCur = 0;
double rowCount = input.GetRowCount(true) ?? double.NaN;
using (var pch = env.StartProgressChannel("Aggregating counts"))
using (var cursor = input.GetRowCursor(col => activeInput[col]))
{
var header = new ProgressHeader(new[] { "rows" });
pch.SetHeader(header, e => { e.SetProgress(0, rowCur, rowCount); });
for (int i = 0; i < size; i++)
{
if (colTypes[i].IsVector)
{
aggregators[i] = GetVecAggregator(cursor, colTypes[i], colSrcs[i]);
}
else
{
aggregators[i] = GetOneAggregator(cursor, colTypes[i], colSrcs[i]);
}
}
while (cursor.MoveNext())
{
for (int i = 0; i < size; i++)
{
aggregators[i].ProcessValue();
}
rowCur++;
}
pch.Checkpoint(rowCur);
}
return(aggregators.Select(a => a.Count).ToArray());
}
