Feature/5820 dataframe extend groupby

[asmirnov82]

Fixes #5820

Extend DataFrame GroupBy operation by adding new property Groupings. This property returns collection of IGrouping objects (the same way as LINQ GroupBy operation does). This allows to use syntacs like this:

var groups = dataFrame.GroupBy<TKey>(columnName).Groupings.ToDictionary(g => g.Key, g => g.ToList()); foreach (DataFrameRow row in groups[KeyValue]) { // any code to work with row object }

[eerhardt]

using System;

Need a copyright header on all new files.

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Refers to: test/Microsoft.Data.Analysis.Tests/DataFrameGroupByTests.cs:1 in 0580710. [](commit_id = 0580710, deletion_comment = False)

[codecov]

Codecov Report

Merging #5821 (4afefd0) into main (7fafbf3) will increase coverage by 0.02%.
The diff coverage is 93.50%.

❗ Current head 4afefd0 differs from pull request most recent head c4d3ad2. Consider uploading reports for the commit c4d3ad2 to get more accurate results

@@            Coverage Diff             @@
##             main    #5821      +/-   ##
==========================================
+ Coverage   68.32%   68.35%   +0.02%     
==========================================
  Files        1131     1132       +1     
  Lines      241291   241368      +77     
  Branches    25053    25059       +6     
==========================================
+ Hits       164863   164978     +115     
+ Misses      69923    69888      -35     
+ Partials     6505     6502       -3     

Flag	Coverage Δ
Debug	68.35% <93.50%> (+0.02%)	⬆️
production	62.96% <80.00%> (+0.02%)	⬆️
test	89.25% <100.00%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
src/Microsoft.Data.Analysis/DataFrame.cs	86.23% <80.00%> (-0.17%)	⬇️
src/Microsoft.Data.Analysis/GroupBy.cs	97.68% <80.00%> (-0.81%)	⬇️
...osoft.Data.Analysis.Tests/DataFrameGroupByTests.cs	100.00% <100.00%> (ø)
...StandardTrainers/Standard/LinearModelParameters.cs	66.32% <0.00%> (+0.25%)	⬆️
src/Microsoft.ML.AutoML/Sweepers/Parameters.cs	85.59% <0.00%> (+0.84%)	⬆️
...rosoft.ML.AutoML/ColumnInference/TextFileSample.cs	62.25% <0.00%> (+2.64%)	⬆️
....ML.AutoML/PipelineSuggesters/PipelineSuggester.cs	85.03% <0.00%> (+3.14%)	⬆️
...c/Microsoft.Data.Analysis/StringDataFrameColumn.cs	70.40% <0.00%> (+6.12%)	⬆️
...c/Microsoft.ML.FastTree/Utils/ThreadTaskManager.cs	100.00% <0.00%> (+20.51%)	⬆️

[pgovind]

I pushed a commit to fix the remaining comments, so we can be ready for the next preview release. Great work here @asmirnov82, thanks!

[eerhardt]