Re: Confusion Matrix

In article
<42ed46a0-c810-4267-8f63-0767f7350985@l32g2000vbp.googlegroups.com>,
 Simon <choonching5u@gmail.com> wrote:


I've never used one larger than second order. I'm not sure why you'd use
a HashMap for a matrix; just use an array of arrays, e.g. int[][]. A Map
associates keys with objects for quick retrieval. You might use a Map to
access values by name rather than index:

<http://en.wikipedia.org/wiki/Confusion_matrix>

<console>
cat dog rab
cat 5 2 0
dog 3 3 2
rab 0 1 11

cat: 8 actual, 7 predicted
dog: 6 actual, 8 predicted
rab: 13 actual, 12 predicted
</console>

<code>
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

/** @author John B. Matthews, distribution per GPL, v2 or later */
public class CMTest {

    public static void main(String[] args) {
        final List<String> list = new ArrayList<String>(
            Arrays.asList("cat", "dog", "rab"));
        final CMatrixModel model = new CMatrixModel(list);
        model.setRow(list.get(0), 5, 2, 0);
        model.setRow(list.get(1), 3, 3, 2);
        model.setRow(list.get(2), 0, 1, 11);
        System.out.println(model);
        for (String s : list) {
            System.out.println(s + ": "
                + model.actual(s) + " actual, "
                + model.predicted(s) + " predicted ");
        }
    }
}

class CMatrixModel extends Object {

    private List<String> names;
    private Map<String, Integer> map =
        new HashMap<String, Integer>();
    private int order;
    private int[][] data;

    CMatrixModel(List<String> names) {
        this.names = names;
        this.order = names.size();
        this.data = new int[order][order];
        int i = 0;
        for (String name : names) {
            map.put(name, i++);
        }
    }

    public void set(String actual, String predicted, int value) {
        int row = map.get(predicted);
        int col = map.get(actual);
        data[row][col] = value;
    }

    public int get(String actual, String predicted) {
        int row = map.get(predicted);
        int col = map.get(actual);
        return data[row][col];
    }

    public void setRow(String predicted, int... actuals) {
        int row = map.get(predicted);
        int col = 0;
        for (int v : actuals) {
            data[row][col++] = v;
        }
    }

    public int actual(String actual) {
        int sumActual = 0;
        for (String s : names) {
            sumActual += this.get(actual, s);
        }
        return sumActual;
    }

    public int predicted(String predicted) {
        int sumPredicted = 0;
        for (String s : names) {
            sumPredicted += this.get(s, predicted);
        }
        return sumPredicted;
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder();
        for (String name : names) {
            sb.append(name);
            sb.append(" ");
        }
        sb.append("\n");
        int i = 0;
        for (int[] row : data) {
            sb.append(names.get(i++));
            sb.append(" ");
            for (int col : row) {
                sb.append(col);
                sb.append(" ");
            }
            sb.append("\n");
        }
        return sb.toString();
    }
}
</code>

[Compiled; error checking omitted.]

--
John B. Matthews
trashgod at gmail dot com
<http://sites.google.com/site/drjohnbmatthews>