Pack multiple column and transfer packed vectors to multi-output gaussian process trainer

modules/stochastic_tools/doc/content/source/reporters/StochasticPackedVector.md

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+# StochasticPackedVector
+
+!syntax description /Reporters/StochasticPackedVector
+
+## Overview
+
+The StochasticPackedVector object allows users to pack multiple scalar sampler columns into a single vector-valued reporter, producing one `std::vector<Real>` per sample. This is especially useful for training multi-output surrogate models using user-generated data. For example, Gaussian Process models using the LMC covariance needs multiple response quantities combined into one vector per sample. The StochasticPackedVector reads rows from a specified Sampler object and collects selected columns into a single vector. Across all samples, this output is represented as `std::vector<std::vector<Real>>`.
+
+
+## Example Syntax
+
+The following is an example of using StochasticPackedVector to pack selected columns in sampler from user-generated data. Here we read the input and output parameters from a user-generated CSV file `sampler_data.csv`
+
+!listing modules/stochastic_tools/test/tests/reporters/stochastic_packed_vector/stochastic_packed_vector.i block=Samplers
+
+The input parameters are transferred via a [StochasticMatrix.md] and the output parameters are transferred and packed via current StochasticPackedVector object. This transfers the results in to the StochasticPackedVector object named `result_pair`.
+
+!listing modules/stochastic_tools/test/tests/reporters/stochastic_packed_vector/stochastic_packed_vector.i block=Reporters
+
+!syntax parameters /Reporters/StochasticPackedVector
+
+!syntax inputs /Reporters/StochasticPackedVector
+
+!syntax children /Reporters/StochasticPackedVector

modules/stochastic_tools/include/reporters/StochasticPackedVector.h

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+//* This file is part of the MOOSE framework
+//* https://mooseframework.inl.gov
+//*
+//* All rights reserved, see COPYRIGHT for full restrictions
+//* https://github.com/idaholab/moose/blob/master/COPYRIGHT
+//*
+//* Licensed under LGPL 2.1, please see LICENSE for details
+//* https://www.gnu.org/licenses/lgpl-2.1.html
+
+#pragma once
+
+// MOOSE includes
+#include "StochasticReporter.h"
+
+class StochasticPackedVector : public StochasticReporter
+{
+public:
+  static InputParameters validParams();
+
+  StochasticPackedVector(const InputParameters & parameters);
+  virtual void execute() override;
+
+protected:
+  // Overriding this to make sure sampler matches
+  virtual ReporterName declareStochasticReporterClone(const Sampler & sampler,
+                                                      const ReporterData & from_data,
+                                                      const ReporterName & from_reporter,
+                                                      std::string prefix = "") override;
+
+  /// The sampler to extract data from
+  Sampler & _sampler;
+
+  /// Column indices to pack (size >= 2)
+  const std::vector<unsigned int> _cols;
+
+private:
+  /// The declared packed output: one vector<Real> per sample
+  std::vector<std::vector<Real>> * _packed_vec;
+};

modules/stochastic_tools/src/reporters/StochasticPackedVector.C

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+//* This file is part of the MOOSE framework
+//* https://mooseframework.inl.gov
+//*
+//* All rights reserved, see COPYRIGHT for full restrictions
+//* https://github.com/idaholab/moose/blob/master/COPYRIGHT
+//*
+//* Licensed under LGPL 2.1, please see LICENSE for details
+//* https://www.gnu.org/licenses/lgpl-2.1.html
+
+#include "StochasticPackedVector.h"
+
+registerMooseObject("StochasticToolsApp", StochasticPackedVector);
+
+InputParameters
+StochasticPackedVector::validParams()
+{
+  InputParameters params = StochasticReporter::validParams();
+  params.addClassDescription(
+      "Packs selected scalar sampler columns into a single vector<Real> per sample.");
+  params.addRequiredParam<SamplerName>("sampler", "The sampler from which to extract rows.");
+  params.addRequiredParam<std::vector<unsigned int>>(
+      "columns", "Zero-based indices of sampler columns to pack (size >= 2).");
+  params.addRequiredParam<ReporterValueName>(
+      "output_name", "Name of the packed vector reporter (vector<Real> per sample).");
+  return params;
+}
+
+StochasticPackedVector::StochasticPackedVector(const InputParameters & parameters)
+  : StochasticReporter(parameters),
+    _sampler(getSampler("sampler")),
+    _cols(getParam<std::vector<unsigned int>>("columns")),
+    _packed_vec(nullptr)
+{
+  if (_cols.size() < 2)
+    paramError("columns", "At least two column indices are required for packing.");
+
+  // Bounds check column indices against sampler width
+  const auto ncols = _sampler.getNumberOfCols();
+  for (auto c : _cols)
+    if (c >= ncols)
+      paramError(
+          "columns", "Column index ", c, " is out of range for sampler with ", ncols, " columns.");
+
+  // Declare the packed reporter (vector<Real> per sample -> vector<vector<Real>> across samples)
+  const auto & out_name = getParam<ReporterValueName>("output_name");
+  _packed_vec = &declareStochasticReporter<std::vector<Real>>(out_name, _sampler);
+}
+
+void
+StochasticPackedVector::execute()
+{
+  // Iterate local rows and pack requested columns into a length-_cols.size() vector
+  for (dof_id_type i = 0; i < _sampler.getNumberOfLocalRows(); ++i)
+  {
+    const std::vector<Real> row = _sampler.getNextLocalRow();
+
+    // Safety: row width must match sampler width
+    if (row.size() != static_cast<size_t>(_sampler.getNumberOfCols()))
+      mooseError("StochasticPackedVector: sampler row width (",
+                 row.size(),
+                 ") does not match sampler column count (",
+                 _sampler.getNumberOfCols(),
+                 ").");
+
+    std::vector<Real> packed;
+    packed.reserve(_cols.size());
+    for (auto c : _cols)
+      packed.push_back(row[c]);
+
+    // Store as the vector for this sample
+    (*_packed_vec)[i] = std::move(packed);
+  }
+}
+
+ReporterName
+StochasticPackedVector::declareStochasticReporterClone(const Sampler & sampler,
+                                                       const ReporterData & from_data,
+                                                       const ReporterName & from_reporter,
+                                                       std::string prefix)
+{
+  if (sampler.name() != _sampler.name())
+    paramError("sampler",
+               "Attempting to create a stochastic value with a different sampler (",
+               sampler.name(),
+               ") than the one specified at input (",
+               _sampler.name(),
+               ").");
+
+  return StochasticReporter::declareStochasticReporterClone(
+      sampler, from_data, from_reporter, prefix);
+}