Creation of components through MLContext and cleanup (Concat, Normalizer, NA Indicator/Replace)

[artidoro]

This PR is part of the work outlined in #1798, and focuses on the Concat, Normalizer, NA Indicator/Replace transformers/estimators:

1. Internalize constructors of estimators and transformers
2. Keep ColumnInfo and move it to to the estimators The ColumnInfo structure should live in the estimators, rather than transformers #1760
3. Rename Arguments -> Options
4. Internalize Options only when they are not used by public constructor. For all other cases, retain Options as public Arguments class should be made internal when possible #1758

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (master@617f7f6). Click here to learn what that means.
The diff coverage is 89.47%.

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Flag	Coverage Δ
#Debug	71.25% <89.47%> (?)
#production	67.61% <86.66%> (?)
#test	85.3% <94.28%> (?)

[sfilipi]

public sealed class ColumnConcatenatingTransformer : RowToRowTransformerBase

one line XML comment; take it form the xtension method. #Closed

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Refers to: src/Microsoft.ML.Data/Transforms/ColumnConcatenatingTransformer.cs:36 in 29cd1ba. [](commit_id = 29cd1ba, deletion_comment = False)

[wschin]

GetOutputSchema [](start = 27, length = 15)

Not a request and probably not related to you. Just feel if we could have documentations for how we compute SchemaShape in GetOutputSchema, we might have documented everything needed by users. #Resolved

[artidoro]

I agree, although I think we should write that in the constructor, or the summary for the class itself. I think we should add it as part of another PR that focuses on improving doc, my PR is a larger set of changes focused on internalization and adding minimal documentation where it was not present.

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In reply to: 253243462 [](ancestors = 253243462)

[sfilipi]

    public IReadOnlyList<(string outputColumnName, string inputColumnName)> Columns => ColumnPairs.AsReadOnly();

xml #Resolved

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Refers to: src/Microsoft.ML.Transforms/MissingValueIndicatorTransformer.cs:81 in 183def8. [](commit_id = 183def8, deletion_comment = False)

[sfilipi]

[abgoswam]

    public sealed class Column : OneToOneColumn

internal ? #Resolved

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Refers to: src/Microsoft.ML.Transforms/MissingValueHandlingTransformer.cs:77 in 183def8. [](commit_id = 183def8, deletion_comment = False)

[wschin]

Time to 🚢

[artidoro]

    public sealed class Column : OneToOneColumn

Same here, I made the entire class internal so this is not an issue.

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In reply to: 460744082 [](ancestors = 460744082)

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Refers to: src/Microsoft.ML.Transforms/MissingValueHandlingTransformer.cs:77 in 183def8. [](commit_id = 183def8, deletion_comment = False)