V1 Scenarios need to be covered by tests

[rogancarr]

In issue #584, we laid out a set of scenarios that we'd like to cover for V1.0 of ML.NET. We need high-level functional tests to make sure that these work well in the 1.0 library.

Here is a list of tests that cover the scenarios. Let's use this issue as a top-level issue to track coverage of the APIs.

Category	Scenarios	Link to Test	Completed PR	Blocked by Issue
Data I/O	I can use objects already in memory (as IEnumerable) as input to my ML pipeline/experiment	Link	#2518
Data I/O	I can use locally stored delimited files (.csv, .tsv, etc.) as input to my ML pipeline/experiment	Link	#2518
Data I/O	I can use locally stored binary files (.idv) as input to my ML pipeline/experiment	Link	#2518
Data I/O	I can go through any arbitrary data transformation / model training and save the output to disk as a delimited file (.csv, .tsv, etc.).	Link	#2518
Data I/O	I can go through any arbitrary data transformation / model training and save the output to disk as a binary file (.idv).	Link	#2518
Data I/O	I can go through any arbitrary data transformation / model training and convert the output to an IEnumerable.	Link	#2518
Data I/O	I can use data from a SQL database by reading it into memory or to disk using an existing SQL reader and then use that as input to my ML pipeline/experiment	(May be a sample)
Data Transformation, Feature Engineering	I can take an existing ONNX model and get predictions from it (as both final output and as input to downstream pipelines)
Data Transformation, Feature Engineering	Extensible transformation: It should be possible to write simple row-mapping transforms.   Examples: "I can add custom steps to my pipeline such as creating a new column that is the addition of two other columns, or easily add cosine similarity, without having to create my own build of ML.NET."		#2803
Data Transformation, Feature Engineering	I can modify settings in the TextFeaturizer to update the number of word-grams and char-grams used along with things like the normalization.		#2803	#2802
Data Transformation, Feature Engineering	I can apply normalization to the columns of my data		#2803
Data Transformation, Feature Engineering	I can take an existing TF model and get predictions from it or any layer in the model		WIP Rogan
Data Transformation and Feature Engineering	P1: I can take an existing TF model and use ML.NET APIs to identify the input and output nodes		WIP Rogan
Debugging	I can see how my data was read in to verify that I specified the schema correctly		#2937
Debugging	I can see the output at the end of my pipeline to see which columns are available (score, probability, predicted label)		#2937
Debugging	I can look at intermediate steps of the pipeline to debug my model.   Example: > I were to have the text "Help I'm a bug!" I should be able to see the steps where it is normalized to "help i'm a bug" then tokenized into ["help", "i'm", "a", "bug"] then mapped into term numbers [203, 25, 3, 511] then projected into the sparse float vector {3:1, 25:1, 203:1, 511:1}, etc. etc.		#2937
Debugging	P1: I can access the information needed for understanding the progress of my training (e.g. number of trees trained so far out of how many)		#2937
Evaluation	I can evaluate a model trained for any of my tasks on test data. The evaluation outputs metrics that are relevant to the task (e.g. AUC, accuracy, P/R, and F1 for binary classification)		#2646
Evaluation	P1: I can get the data that will allow me to plot PR curves		#2646	#2645
Explainability & Interpretability	I can get near-free (local) feature importance for scored examples (Feature Contributions)		#2584
Explainability & Interpretability	I can view how much each feature contributed to each prediction for trees and linear models (Feature Contributions)		#2584
Explainability & Interpretability	I can view the overall importance of each feature (Permutation Feature Importance, GetFeatureWeights)		#2584
Explainability & Interpretability	I can train interpretable models (linear model, GAM)
Introspective training	I can take an existing model file and inspect what transformers were included in the pipeline		#2859
Introspective training	I can inspect the coefficients (weights and bias) of a linear model without much work. Easy to find via auto-complete.		#2859
Introspective training	I can inspect the normalization coefficients of a normalizer in my pipeline without much work. Easy to find via auto-complete.		#2859
Introspective training	I can inspect the trees of a boosted decision tree model without much work. Easy to find via auto-complete.		#2859
Introspective training	I can inspect the topics after training an LDA transform. Easy to find via auto-complete.		#2859
Introspective training	I can inspect a categorical transform and see which feature values map to which key values. Easy to find via auto-complete.		#2859
Introspective training	I can access the GAM feature histograms through APIs		#2859
Model files	I can train a model and save it as a file. This model includes the learner as well as the transforms (e.g. Decomposability)
Model files	I can use a model file in a completely different process to make predictions. (e.g. Decomposability)
Model files	I can use newer versions of ML.NET with ML.NET model files of previous versions (for v1.x)		test in V1.1
Model files	I can easily figure out which NuGets (and versions) I need to score an ML.NET model
Model files	P2: I can move data between NimbusML and ML.NET (using IDV). Prepare with NimbusML and load with ML.NET		V1.1
Model files	P2: I can use model files interchangeably between compatible versions of ML.NET and NimbusML.		V1.1
Model files	P1: I can export ML.NET models to ONNX (limited to the existing internal functionality)
Model files	I can save a model to text		V1.1
Prediction	I can get predictions (scores, probabilities, predicted labels) for every row in a test dataset
Prediction	I can reconfigure the threshold of my binary classification model based on analysis of the PR curves or other metrics scores.	Link		#2465
Prediction	(Might not work?) I can map the score/probability for each class to the original class labels I provided in the pipeline (multiclass, binary classification).
Tasks	I can train a model to do classification (binary and multiclass)		#2646
Tasks	I can train a model to do regression		#2646
Tasks	I can train a model to do anomaly detection		#2646
Tasks	I can train a model to do recommendations		#2646
Tasks	I can train a model to do ranking		#2646
Tasks	I can train a model to do clustering		#2646
Training	I can provide multiple learners and easily compare evaluation metrics between them.		#2921
Training	I can use an initial predictor to update/train the model for some trainers (e.g. linear learners like averaged perceptron). Specifically, start the weights for the model from the existing weights.		#2921
Training	Metacomponents smartly restrict their use to compatible components.   Example: "When specifying what trainer OVA should use, a user will be able to specify any binary classifier. If they specify a regression or multi-class classifier ideally that should be a compile error."		#2921
Training	I can train TF models when I bring a TF model topology		WIP Rogan
Training	I can use OVA and easily add any binary classifier to it		#2921
Use in web environments	I can use ML.NET models to make predictions in multi-threaded environments like ASP.NET. (This doesn't have to be inherent in the prediction engine but should be easy to do.)
Validation	Cross-validation: I can take a pipeline and easily do cross validation on it without having to know how CV works.	Link	#2470
Validation	I can use a validation set in a pipeline for learners that support them (e.g. FastTree, GAM)	Link	#2503

[endintiers]

So we aren't going to support training from an IEnumerable (directly) backed by an EF DbContext in V1? If so better note that somewhere, because it works up to a point and then fails in a confusing way.

[rogancarr]

@endintiers For V1, we will only support training with IDataView, but that should still be possible with an IEnumerable backed by an EF DbContext. (@singlis and @Ivanidzo4ka)

Would you mind giving an example of what you've been doing and how it's been failing?

[Ivanidzo4ka]

#2159 for more details.

The actual problem is that EF Core DBContexts aren't thread-safe, so if cursors from multiple threads exhaust the pool and more than one tries to access the Enumerable to get more: 'boom'

I believe setting conc to 1 for mlContext should help, but it need verification.

[rogancarr]

Adding SQL test back — I had misunderstood the requirements, and it looks like we can use an EF DbContext for it.

[endintiers]

Tar. I have looked at how to modify mlContext.CreateStreamingDataView to be able to detect? and create an IDataView that could signal 'single-threaded source' downstream. This could be done (it's just the sync of buffer re-loads that is an issue). Given the time release-wise though just setting conc to 1 is a good move. Sadly this will slow training (on serious datasets with many available CPUs). I should volunteer to do at least this test... (using EF Core In-Memory). In the real world generating text files from the DB and training on them instead seems to be the best move.