Dataset (and ModifiableDataset) constructor accepts unsupported values

[bburlacu]

For example, passing an int array to the constructor will work just fine:

var dataset = new Dataset(new[] { "x" }, new[] { new[] { 1, 2, 3 } });

but trying to get the values by calling

var values = dataset.GetDoubleValues("x");

will throw an exception because variable x is not of type double.

The constructor should check for value types and throw an exception if an incompatible type is provided.

Additionally,

• the AddVariable method of the ModifiableDataset does not behave properly when the dataset is empty.

• the AddVariable method clones the values while the constructor does not

The ModifiableDataset was introduced with #2276.

[bburlacu]

r15769: Add type checks in Dataset constructor, remove cloning of values in the ModifiableDataset.AddVariable method. Provide small fix in GradientBoostingRegressionAlgorithm for AddVariable.

[mkommend]

Please verify that the data is cloned when handed to the Dataset, because it should not be possible to modify the data contained in the Dataset at all. However, this changes if a ModifiableDataset is used, because their modification is encouraged and thus the data should not be cloned.

[bburlacu]

r15829: Ensure cloning only happens in the Dataset constructor and ModifiableDataset cloning constructor.

[mkommend]

Please assign a milestone on every ticket, especially if it contains trunk commits!

[mkommend]

r16124: Merged r15769 and r15829 into stable.