/*******************************************************************************
* Copyright (c) 2010 Haifeng Li
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*******************************************************************************/
package smile.validation;
/**
* The precision or positive predictive value (PPV) is ratio of true positives
* to combined true and false positives, which is different from sensitivity.
* <p>
* PPV = TP / (TP + FP)
*
* @author Haifeng Li
*/
public class Precision implements ClassificationMeasure {
@Override
public double measure(int[] truth, int[] prediction) {
if (truth.length != prediction.length) {
throw new IllegalArgumentException(String.format("The vector sizes don't match: %d != %d.", truth.length, prediction.length));
}
int tp = 0;
int p = 0;
for (int i = 0; i < truth.length; i++) {
if (prediction[i] == 1) {
p++;
if (truth[i] == 1) {
tp++;
}
}
}
return (double) tp / p;
}
@Override
public String toString() {
return "Precision";
}
}