Lambda expression, from Python to C#

Question

I am trying to rewrite some thing from python to c#, I have managed to recreate the dictionaries I but I am having trouble understanding the dictionary comprehension in c#. here is the python code I would like to recreate in c#

distances={1:.02,30:.001,1000:.001}
minSearch=(min(distances.items(), key=lambda x:x[1]))

this is the dictionary I have in c#

Dictionary<int, double> distDict = new Dictionary<int, double>();

Thanks for the answer here it is implemented

                List<MapPoint> list = new List<MapPoint>();
                list.Add(pointDict[Convert.ToInt32(startOid)]);
                while (pointDict.Count()>1)
                {
                    var shape = pointDict[Convert.ToInt32(startOid)];
                    pointDict.Remove(Convert.ToInt32(startOid));
                    var X = shape.X;
                    var Y = shape.Y;
                    var Z = shape.Z;
                    foreach(KeyValuePair<int,MapPoint> point in pointDict)
                    {
                        var X2 = point.Value.X;
                        var Y2 = point.Value.Y;
                        var Z2 = point.Value.Z;
                        var squaredZDist = Math.Pow((Z - Z2), 2);
                        var squaredDist = Math.Pow(Math.Sqrt(Math.Pow(X - X2, 2) + Math.Pow(Y - Y2, 2)),2);
                        var threeDSquaredDist = Math.Sqrt(squaredDist + squaredZDist);
                        distDict[point.Key] = threeDSquaredDist;
                    }
                    var minValue = distDict.Min(x => x.Value);
                    var minPair = distDict
                                    .Where(x => x.Value == minValue)
                                    .First();
                    startOid = minPair.Key;
                    list.Add(pointDict[minPair.Key]);

                    distDict.Clear();
                }
                Polyline polyline = PolylineBuilder.CreatePolyline(list);
                var pipeLayer = mapView.Map.Layers.OfType<FeatureLayer>()
                                                    .Where(x=>x.Name == "PIPELINE")
                                                    .First();
                MessageBox.Show(pipeLayer.Name.ToString());
                var createFeatures = new EditOperation();
                createFeatures.Name = "Create Polyline";
                createFeatures.Create(pipeLayer, polyline);
                createFeatures.Execute();

Paul D'Ambra · Accepted Answer · 2018-10-14 19:05:01Z

1

you can duplicate that python using:

var distDict = new Dictionary<int, double> {
  {1,.02},{30,.001},{1000,.001}
};
var minValue = distDict.Min(x => x.Value);
var minPair = distDict
                .Where(x => x.Value == minValue)
                .First();
var expected = new KeyValuePair<int, double>(30, .001);
Assert.Equal(expected, minPair);

answered Oct 14, 2018 at 19:05

Paul D'Ambra

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1 Comment

Gary Lester Over a year ago

The answer worked perfectly. Thank you very much. I posted the implementation above in the question.

willeM_ Van Onsem · Accepted Answer · 2018-10-14 19:52:35Z

1

We can do this with:

KeyValuePair<int, double> minSearch = distDict.OrderBy(x => x.Value).First()

This is thus a KeyValuePair<int, double> that contains a Key and Value property of the dictionary entry with the smallest Value in the `Dictionary.

C# will not order the collection immediately with .OrderBy(..), but construct an OrderedEnumerable [GitHub]. This will normally result in the fact that the .First() will aim to calculate the smallest item in linear time, so O(n), and like @flakes says, constant memory complexity O(1).

edited Oct 14, 2018 at 19:52

answered Oct 14, 2018 at 18:53

willeM_ Van Onsem

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3 Comments

flakes Over a year ago

Cool! I never knew that about OrderedEnumerable. I always assumed that OrderBy does a complete sort.

willeM_ Van Onsem Over a year ago

@flakes: well of course if you enumerate over the items, it eventually performs a full sort, but .First() should normally work in linear time.

flakes Over a year ago

And O(1) for memory complexity is also super nice.

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