1 | using System;
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2 | using System.Collections.Generic;
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3 | using System.Linq;
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4 | using System.Text;
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5 | using System.Threading.Tasks;
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6 |
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7 | namespace HeuristicLab.Common {
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8 | public static class Extensions {
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9 | public static bool IsAlmost(this double x, double y) {
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10 | return Math.Abs(x - y) < 1.0e-12;
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11 | }
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12 |
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13 | public static T SelectRandom<T>(this IEnumerable<T> xs, Random rand) {
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14 | var n = xs.Count();
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15 | return xs.ElementAt(rand.Next(n));
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16 | }
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17 |
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18 | public static T SampleProportional<T>(this IEnumerable<T> elements, Random random, IEnumerable<double> weights) {
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19 | double total = weights.Sum();
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20 |
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21 | var elemEnumerator = elements.GetEnumerator();
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22 | elemEnumerator.MoveNext();
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23 | var weightEnumerator = weights.GetEnumerator();
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24 | weightEnumerator.MoveNext();
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25 |
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26 | var r = random.NextDouble() * total;
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27 | var agg = weightEnumerator.Current;
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28 |
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29 | while (agg < r) {
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30 | weightEnumerator.MoveNext();
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31 | elemEnumerator.MoveNext();
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32 | agg += weightEnumerator.Current;
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33 | }
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34 | return elemEnumerator.Current;
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35 | }
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36 |
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37 | public static double RSq(IEnumerable<double> xs, IEnumerable<double> ys) {
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38 | // two pass implementation, but we don't care
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39 | var meanX = xs.Average();
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40 | var meanY = ys.Average();
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41 |
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42 | var s = 0.0;
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43 | var ssX = 0.0;
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44 | var ssY = 0.0;
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45 | var xEnum = xs.GetEnumerator();
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46 | var yEnum = ys.GetEnumerator();
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47 | while (xEnum.MoveNext() & yEnum.MoveNext()) {
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48 | var x = xEnum.Current;
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49 | var y = yEnum.Current;
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50 | s += (x - meanX) * (y - meanY);
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51 | ssX += (x - meanX) * (x - meanX);
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52 | ssY += (y - meanY) * (y - meanY);
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53 | }
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54 | if (xEnum.MoveNext() | yEnum.MoveNext()) throw new ArgumentException("lengths are not equal");
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55 |
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56 | if (s.IsAlmost(0)) return 0;
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57 | if (ssX.IsAlmost(0) || ssY.IsAlmost(0)) return 0;
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58 | return s * s / (ssX * ssY);
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59 | }
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60 |
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61 |
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62 | }
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63 | }
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