Print out confusion matrix with JAVA

Question

This might sound stupid! But, I count find any simple example to reference! Can someone please give an example of printing confusion matrix using java?

something like this (the output):

p\a   Head    Tail
Head    1      4
Tail    4      1

Assuming the data stored in HashMap like this

HashMap<String,Integer>
String = "Head, Tail"
Integer = 4

update (sample code):

public static void main(String[] args) {

        HashMap<String,Integer> cmatrix = new HashMap<String,Integer>();

        //the string part can hold more the 2 values, all separated with comma
        cmatrix.put("tail, head", 1);
        cmatrix.put("head ,tail", 4);
        cmatrix.put("tail, tail", 1);
        cmatrix.put("head, head", 4);

        for (Map.Entry entry : cmatrix.entrySet()) {
            System.out.println(entry.getKey() +" : "+entry.getValue());
        }
    }

thanks!

Answer 1

To simplify the code, let's assume no spaces in the source data:

cmatrix.put("tail,head", 1);
cmatrix.put("head,tail", 4);
cmatrix.put("tail,tail", 1);
cmatrix.put("head,head", 4);

First, we need to gather the names of the classes:

Set<String> classNames = new HashSet<String>();
for(String key : cmatrix.keySet()) {
    String[] classes = key.split(",");
    if(classes != null && classes.length > 0) {
        classNames.addAll(Arrays.asList(classes));
    }
}

Next, sort the class names:

List<String> sortedClassNames = new ArrayList<String>();
sortedClassNames.addAll(classNames);
Collections.sort(sortedClassNames);

Then print out the header row.

System.out.print("p/a");
for(String predictedClassName : sortedClassNames) {
    System.out.print("\t" + predictedClassName);
}
System.out.println();

Then print out each line:

for(String actualClassName : sortedClassNames) {
    System.out.print(actualClassName);
    for(String predictedClassName : sortedClassNames) {
        Integer value = cmatrix.get(actualClassName + "," + predictedClassName);
        System.out.print("\t");
        if(value != null) {
            System.out.print(value);
        }
    }
    System.out.println();
}

I'll leave the 'prettying up' of the output as an exercise for the reader.