TableSlice extends Relation { public double reduce(String numberColumnName, NumericAggregateFunction function) { NumericColumn<?> column = table.numberColumn(numberColumnName); if (hasSelection()) { return function.summarize(column.where(selection)); } return function.summarize(column); } TableSlice(Table table, Selection rowSelection);  TableSlice(Table table); @Override Column<?> column(int columnIndex); @Override Column<?> column(String columnName); @Override int columnCount(); @Override int rowCount(); @Override List<Column<?>> columns(); @Override int columnIndex(Column<?> column); @Override Object get(int r, int c); @Override String name(); Table getTable(); @Override void clear(); void removeSort(); void removeSelection(); @Override List<String> columnNames(); @Override TableSlice addColumns(Column<?>... column); @Override TableSlice removeColumns(Column<?>... columns); @Override Table first(int nRows); @Override TableSlice setName(String name); Table asTable(); double reduce(String numberColumnName, NumericAggregateFunction function); @Override Iterator<Row> iterator(); int mappedRowNumber(int rowNumber); void sortOn(Sort key);  }
@Test public void reduce() throws Exception { source = Table.read().csv("../data/bush.csv"); TableSlice slice = new TableSlice(source, Selection.with(2)); assertEquals(58.0, slice.reduce("approval", sum), 0.0001); }
@Test public void reduceNoSelection() throws Exception { source = Table.read().csv("../data/bush.csv"); TableSlice slice = new TableSlice(source); assertEquals(20957.0, slice.reduce("approval", sum), 0.0001); }