pivot static method

Datacat pivot(Datacat datacat, String indexColumn, String pivotColumn, String valueColumn,)

Creates a pivot Datacat from datacat using indexColumn for rows, pivotColumn for new column headers, and valueColumn for values. Aggregates values using sum.

Implementation

static Datacat pivot(Datacat datacat, String indexColumn, String pivotColumn,
    String valueColumn) {
  int indexCol = datacat.columns.indexOf(indexColumn);
  int pivotCol = datacat.columns.indexOf(pivotColumn);
  int valueCol = datacat.columns.indexOf(valueColumn);
  if (indexCol == -1 || pivotCol == -1 || valueCol == -1) {
    throw ArgumentError('One or more specified columns not found.');
  }
  Map<dynamic, List<List<dynamic>>> groups = {};
  for (var row in datacat.rows) {
    var key = row[indexCol];
    groups.putIfAbsent(key, () => []).add(row);
  }
  Set<dynamic> pivotValues = {};
  for (var row in datacat.rows) {
    pivotValues.add(row[pivotCol]);
  }
  List<String> newColumns = [
    indexColumn,
    ...pivotValues.map((v) => v.toString()).toList()
  ];
  List<List<dynamic>> newRows = [];
  groups.forEach((key, groupRows) {
    Map<String, num> aggregation = {};
    for (var pv in pivotValues) {
      aggregation[pv.toString()] = 0;
    }
    for (var row in groupRows) {
      var pVal = row[pivotCol];
      var value = row[valueCol];
      if (value is num) {
        aggregation[pVal.toString()] = aggregation[pVal.toString()]! + value;
      }
    }
    List<dynamic> newRow = [key];
    for (var pv in pivotValues) {
      newRow.add(aggregation[pv.toString()]);
    }
    newRows.add(newRow);
  });
  return Datacat(columns: newColumns, rows: newRows);
}