Saving a DataView to a file should be simpler and not through to the LocalEnvironment class

[CESARDELATORRE]

I'm using v0.7.
Issue: Saving a DataView to a file should be simpler and not having to directly use the LocalEnvironment class.
If there's any new way to do this in v0.7 or v08, please tell me, but I haven't found it. :)

As far as I know, this is the code needed, currently:

                // save test split dataset
                IHostEnvironment env = (IHostEnvironment)mlContext;
                using (var ch = env.Start("SaveData"))
                using (var file = env.CreateOutputFile(Path.Combine(_outputPath, "testData.idv")))
                {
                    var saver = new BinarySaver(mlContext, new BinarySaver.Arguments());
                    DataSaverUtils.SaveDataView(ch, saver, testDataView, file);
                }

First, it needs to use the IChannel object that has to be obtained from the IHostEnvironment object that you can get by casting the MLContext object to IHostEnvironment. The developer shouldn't need to use IHostEnvironment in any case, I think.

Then, still a few more lines for saving the file.

We should aim to achieve a simpler API for doing this, just something like:

testDataView.SaveToFile(testDataSetFilePath);

Or if we need to do it through any utility class:

DataSaverUtils.SaveDataViewToFile(testDataView, testDataSetFilePath);

[TomFinley]

MLContext.Data.SaveAsText -- generally the common idiom in 0.7 and going forward we think will be that this will be the central structure to "find" commonly used operations. Please refer to #1098 to familiarize yourself with the idiom.

Sort of a factory of everything. That's not an antipattern, is it? 😉