added linear regression line for trend analysis, see issue #436

android_app/app/src/main/java/com/health/openscale/gui/views/ChartMeasurementView.java

@@ -139,6 +139,7 @@ public class ChartMeasurementView extends LineChart {
         isAnimationOn = true;
         isInGraphKey = true;
 
+        setHardwareAccelerationEnabled(true);
         setMarker(new ChartMarkerView(getContext(), R.layout.chart_markerview));
         setDoubleTapToZoomEnabled(false);
         setHighlightPerTapEnabled(true);
@@ -512,10 +513,6 @@ public class ChartMeasurementView extends LineChart {
                     entry.setData(extraData);
 
                     lineEntries.add(entry);
-
-                    /*if (prefs.getBoolean("regressionLine", false) && measurementView instanceof WeightMeasurementView) {
-                        polyFitter.addPoint((double)entry.getX(), (double)entry.getY());
-                    }*/
                 }
 
                 addMeasurementLine(lineDataSets, lineEntries, measurementView);
@@ -523,7 +520,10 @@ public class ChartMeasurementView extends LineChart {
         }
 
         addGoalLine(lineDataSets);
-        // addRegressionLine(lineDataSets); TODO replaced it with an sliding average
+
+        if (isInGraphKey) {
+            addRegressionLine(lineDataSets);
+        }
 
         LineData data = new LineData(lineDataSets);
         setData(data);
@@ -607,7 +607,6 @@ public class ChartMeasurementView extends LineChart {
         }
     }
 
-    // TODO replace with sliding average
     private void addRegressionLine(List<ILineDataSet> lineDataSets) {
         if (prefs.getBoolean("regressionLine", false)) {
             int regressLineOrder = 1;
@@ -619,27 +618,40 @@ public class ChartMeasurementView extends LineChart {
                 prefs.edit().putString("regressionLineOrder", "1").apply();
             }
 
-            PolynomialFitter polyFitter = new PolynomialFitter(Math.min(regressLineOrder, 100));
+            List<ILineDataSet> regressionLineDataSets = new ArrayList<>();
 
-            PolynomialFitter.Polynomial polynomial = polyFitter.getBestFit();
+            for (ILineDataSet dataSet : lineDataSets) {
+                PolynomialFitter polyFitter = new PolynomialFitter(Math.min(regressLineOrder, 100));
 
-            List<Entry> valuesLinearRegression = new Stack<>();
+                for (int i=0; i<dataSet.getEntryCount(); i++) {
+                    Entry entry = dataSet.getEntryForIndex(i);
+                    polyFitter.addPoint((double) entry.getX(), (double) entry.getY());
+                }
 
-            for (int i = minXValue; i < maxXValue; i++) {
+                PolynomialFitter.Polynomial polynomial = polyFitter.getBestFit();
-                double y_value = polynomial.getY(i);
+
-                valuesLinearRegression.add(new Entry((float) i, (float) y_value));
+                List<Entry> valuesLinearRegression = new Stack<>();
+
+                for (int i = minXValue; i < maxXValue; i++) {
+                    double y_value = polynomial.getY(i);
+                    valuesLinearRegression.add(new Entry((float) i, (float) y_value));
+                }
+
+                LineDataSet linearRegressionLine = new LineDataSet(valuesLinearRegression, dataSet.getLabel() + "-" + getContext().getString(R.string.label_regression_line));
+                linearRegressionLine.setLineWidth(1.5f);
+                linearRegressionLine.setColor(dataSet.getColor());
+                linearRegressionLine.setAxisDependency(dataSet.getAxisDependency());
+                linearRegressionLine.setDrawValues(false);
+                linearRegressionLine.setDrawCircles(false);
+                linearRegressionLine.setHighlightEnabled(false);
+                linearRegressionLine.enableDashedLine(10, 30, 0);
+
+                regressionLineDataSets.add(linearRegressionLine);
             }
 
-            LineDataSet linearRegressionLine = new LineDataSet(valuesLinearRegression, getContext().getString(R.string.label_regression_line));
+            for (ILineDataSet dataSet : regressionLineDataSets) {
-            linearRegressionLine.setLineWidth(1.5f);
+                lineDataSets.add(dataSet);
-            linearRegressionLine.setColor(ColorUtil.COLOR_VIOLET);
+            }
-            linearRegressionLine.setAxisDependency(prefs.getBoolean("weightOnRightAxis", true) ? YAxis.AxisDependency.RIGHT : YAxis.AxisDependency.LEFT);
-            linearRegressionLine.setDrawValues(false);
-            linearRegressionLine.setDrawCircles(false);
-            linearRegressionLine.setHighlightEnabled(false);
-            linearRegressionLine.enableDashedLine(10, 30, 0);
-
-            lineDataSets.add(linearRegressionLine);
         }
     }
 }

android_app/app/src/main/res/values-de/strings.xml

@@ -110,7 +110,7 @@
     <string name="error_initial_weight_required">Fehler: Anfangsgewicht ist erforderlich</string>
     <string name="label_bt_device_no_support">Gerät wird nicht unterstützt</string>
     <string name="label_goal_line">Ziellinie</string>
-    <string name="label_regression_line">Gewichtsregressionsgerade</string>
+    <string name="label_regression_line">Regressionsgerade</string>
     <string name="label_regression_line_degree">Polynomischer Regressions-Grad</string>
     <string name="label_bluetooth_searching">Suche nach Ihrer Bluetooth Waagen</string>
     <string name="label_bone">Knochenmasse</string>

android_app/app/src/main/res/values/strings.xml

@@ -136,7 +136,7 @@
     <string name="label_not_found">not found</string>
     <string name="label_ignoreOutOfRange">Ignore out of range data</string>
     <string name="label_initial_weight">Initial weight</string>
-    <string name="label_regression_line">Regression weight line</string>
+    <string name="label_regression_line">Regression line</string>
     <string name="label_regression_line_degree">Regression polynomial degree</string>
     <string name="label_goal_line">Goal line</string>
     <string name="label_help">Help</string>

android_app/app/src/main/res/xml/graph_preferences.xml

@@ -24,7 +24,6 @@
         android:summaryOff="@string/info_is_not_visible"
         android:summaryOn="@string/info_is_visible"
         android:title="@string/label_goal_line" />
-    <!--
     <CheckBoxPreference
         android:defaultValue="false"
         android:key="regressionLine"
@@ -36,5 +35,4 @@
         android:dependency="regressionLine"
         android:key="regressionLineOrder"
         android:title="@string/label_regression_line_degree" />
-    -->
 </PreferenceScreen>