add dispersion

src/main/java/ru/ulstu/statistic/StatisticService.java

@@ -26,18 +26,27 @@ public class StatisticService {
         return getOptionalValue(Double.valueOf(timeSeries.getLength()));
     }
 
+    public Optional<Double> getDispersion(TimeSeries timeSeries) {
+        Optional<Double> maybeAverage = getAverage(timeSeries);
+        return getOptionalValue(maybeAverage.isPresent()
+                ? timeSeries.getValues().stream().mapToDouble(v -> Math.pow(v.getValue() - maybeAverage.get(), 2)).sum() / timeSeries.getLength()
+                : null);
+    }
 
     private DoubleStream getDoubleStream(TimeSeries timeSeries) {
         return timeSeries.getValues().stream().mapToDouble(TimeSeriesValue::getValue);
     }
 
     private Optional<Double> getOptionalValue(OptionalDouble optionalDouble) {
-        return Optional.ofNullable(optionalDouble.isPresent()
+        return getOptionalValue(optionalDouble.isPresent()
                 ? optionalDouble.getAsDouble()
                 : null);
     }
 
     private Optional<Double> getOptionalValue(Double value) {
+        value = (value == null)
+                ? null
+                : ((double) Math.round(value * 100) / 100);
         return Optional.ofNullable(value);
     }
 
@@ -45,6 +54,7 @@ public class StatisticService {
         return new TimeSeriesStatistic(getMin(timeSeries),
                 getMax(timeSeries),
                 getAverage(timeSeries),
-                getLength(timeSeries));
+                getLength(timeSeries),
+                getDispersion(timeSeries));
     }
 }

src/main/java/ru/ulstu/statistic/TimeSeriesStatistic.java

@@ -8,14 +8,18 @@ public class TimeSeriesStatistic {
     private Optional<Double> average;
     private Optional<Double> length;
 
+    private Optional<Double> dispersion;
+
     public TimeSeriesStatistic(Optional<Double> min,
                                Optional<Double> max,
                                Optional<Double> average,
-                               Optional<Double> length) {
+                               Optional<Double> length,
+                               Optional<Double> dispersion) {
         this.min = min;
         this.max = max;
         this.average = average;
         this.length = length;
+        this.dispersion = dispersion;
     }
 
     public Optional<Double> getMin() {
@@ -33,4 +37,8 @@ public class TimeSeriesStatistic {
     public Optional<Double> getLength() {
         return length;
     }
+
+    public Optional<Double> getDispersion() {
+        return dispersion;
+    }
 }

src/main/resources/templates/index.html

@@ -161,6 +161,10 @@
                         <span th:text="${statistic.average.present ? statistic.average.get : 'Не известно'}"/>
                     </p>
                     <hr/>
+                    <p> Дисперсия:
+                        <span th:text="${statistic.dispersion.present ? statistic.dispersion    .get : 'Не известно'}"/>
+                    </p>
+                    <hr/>
                 </div>
             </div>
             <div class="col-md-12 col-sm-12 col-lg-6">