Simple moving average on the chart (#968)

* Added simple moving average to the graph

* Fixed comments

* Removed moving average label from the legend

* Revert "Removed moving average label from the legend"

This reverts commit e7b324ff89.

* Refactored trendline computation code and settings

* Removed using the old simple moving average preferences key

* Moved trendline computations methods names to a different class, renamed the interface and reordered menu items

* Removed unnecessary imports

* moved static strings for chart computation method to ChartMeasurementView

* scroll to the new moving average preference

* renaming the internal strings

---------

Co-authored-by: oliexdev <olie.xdev@googlemail.com>

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

@@ -56,6 +56,9 @@ import java.util.List;
 import java.util.Stack;
 
 public class ChartMeasurementView extends LineChart {
+    public static final String COMPUTATION_METHOD_SIMPLE_MOVING_AVERAGE = "SimpleMovingAverage";
+    public static final String COMPUTATION_METHOD_EXPONENTIALLY_SMOOTHED_MOVING_AVERAGE = "ExponentiallySmoothedMovingAverage";
+
     public enum ViewMode {
         DAY_OF_MONTH,
         WEEK_OF_MONTH,
@@ -76,6 +79,10 @@ public class ChartMeasurementView extends LineChart {
     private boolean isInGraphKey;
     private ProgressBar progressBar;
 
+    private interface TrendlineComputationInterface {
+        public List<ScaleMeasurement> processMeasurements(List<ScaleMeasurement> measurementList);
+    }
+
     public ChartMeasurementView(Context context) {
         super(context);
         initChart();
@@ -400,7 +407,19 @@ public class ChartMeasurementView extends LineChart {
         }
 
         if (prefs.getBoolean("trendLine", false)) {
-            addTrendLine(lineDataSets);
+            String selectedTrendLineComputationMethod = prefs.getString("trendlineComputationMethod", COMPUTATION_METHOD_EXPONENTIALLY_SMOOTHED_MOVING_AVERAGE);
+            switch (selectedTrendLineComputationMethod) {
+                case COMPUTATION_METHOD_EXPONENTIALLY_SMOOTHED_MOVING_AVERAGE:
+                    addExponentiallySmoothedMovingAverage(lineDataSets);
+                    break;
+                case COMPUTATION_METHOD_SIMPLE_MOVING_AVERAGE:
+                    addSimpleMovingAverage(lineDataSets);
+                    break;
+                default:
+                    addExponentiallySmoothedMovingAverage(lineDataSets);
+                    break; // by default fall back to exponentially smoothed moving average
+            }
+
         }
 
         if (!lineDataSets.isEmpty()) {
@@ -417,6 +436,14 @@ public class ChartMeasurementView extends LineChart {
         progressBar.setVisibility(GONE);
     }
 
+    private void addExponentiallySmoothedMovingAverage(List<ILineDataSet> lineDataSets) {
+        addTrendLine(lineDataSets, this::getExponentiallySmoothedMovingAverageOfScaleMeasurements);
+    }
+
+    private void addSimpleMovingAverage(List<ILineDataSet> lineDataSets) {
+        addTrendLine(lineDataSets, this::getSimpleMovingAverageOfScaleMeasurements);
+    }
+
     private void addMeasurementLine(List<ILineDataSet> lineDataSets, List<Entry> lineEntries, FloatMeasurementView measurementView) {
         LineDataSet measurementLine = new LineDataSet(lineEntries, measurementView.getName().toString());
         measurementLine.setLineWidth(1.5f);
@@ -435,7 +462,7 @@ public class ChartMeasurementView extends LineChart {
         measurementLine.setDrawValues(prefs.getBoolean("labelsEnable", false));
         measurementLine.setMode(LineDataSet.Mode.HORIZONTAL_BEZIER);
         if (prefs.getBoolean("trendLine", false)) {
-            // show only data point if trend line is enabled
+            // show only data points if trend line or simple moving average is enabled
             measurementLine.enableDashedLine(0, 1, 0);
         }
 
@@ -473,7 +500,7 @@ public class ChartMeasurementView extends LineChart {
         lineDataSets.add(goalLine);
     }
 
-    private List<ScaleMeasurement> getScaleMeasurementsAsTrendline(List<ScaleMeasurement> measurementList) {
+    private List<ScaleMeasurement> getExponentiallySmoothedMovingAverageOfScaleMeasurements(List<ScaleMeasurement> measurementList) {
         List<ScaleMeasurement> trendlineList = new ArrayList<>();
 
        // exponentially smoothed moving average with 10% smoothing
@@ -493,56 +520,100 @@ public class ChartMeasurementView extends LineChart {
         return trendlineList;
     }
 
-    private void addTrendLine(List<ILineDataSet> lineDataSets) {
+    private List<ScaleMeasurement> getSimpleMovingAverageOfScaleMeasurements(List<ScaleMeasurement> measurementList) {
+        final long NUMBER_OF_MS_IN_A_DAY = 1000 * 60 * 60 * 24;
+        List<ScaleMeasurement> movingAverageList = new ArrayList<>();
+
+        int samplingWidth = prefs.getInt("simpleMovingAverageNumDays", 7);
+
+        // simple moving average of the last samplingWidth days
+        movingAverageList.add(measurementList.get(0));
+
+        for (int i = 1; i < measurementList.size(); i++) {
+            ScaleMeasurement entry = measurementList.get(i).clone();
+            int numberOfMeasurementsToAverageOut = 0;
+
+            for (int k = i-1; k >= 0; k--){
+                ScaleMeasurement previousMeasurement = measurementList.get(i - k - 1);
+
+                if (entry.getDateTime().getTime() - previousMeasurement.getDateTime().getTime() < samplingWidth * NUMBER_OF_MS_IN_A_DAY) {
+                    numberOfMeasurementsToAverageOut += 1;
+                    entry.add(previousMeasurement);
+                }
+            }
+
+            entry.multiply(1.0f/(numberOfMeasurementsToAverageOut+1));
+
+            movingAverageList.add(entry);
+        }
+
+        return movingAverageList;
+    }
+
+    private ArrayList<ScaleMeasurement> getNonZeroScaleMeasurementsList(FloatMeasurementView measurementView) {
+        ArrayList<ScaleMeasurement> nonZeroScaleMeasurementList = new ArrayList<>();
+
+        // filter first all zero measurements out, so that the follow-up trendline calculations are not based on them
+        for (int i=0; i<scaleMeasurementList.size(); i++) {
+            ScaleMeasurement measurement = scaleMeasurementList.get(i);
+            float value = measurementView.getMeasurementValue(measurement);
+
+            if (value != 0.0f) {
+                nonZeroScaleMeasurementList.add(measurement);
+            }
+        }
+
+        return nonZeroScaleMeasurementList;
+    }
+
+    private void addTrendLine(List<ILineDataSet> lineDataSets, TrendlineComputationInterface trendlineComputation) {
 
         for (MeasurementView view : measurementViews) {
             if (view instanceof FloatMeasurementView && view.isVisible()) {
                 final FloatMeasurementView measurementView = (FloatMeasurementView) view;
 
-                final List<Entry> lineEntries = new ArrayList<>();
-
-                ArrayList<ScaleMeasurement> nonZeroScaleMeasurementList = new ArrayList<>();
-
-                // filter first all zero measurements out, so that the follow-up trendline calculations are not based on them
-                for (int i=0; i<scaleMeasurementList.size(); i++) {
-                    ScaleMeasurement measurement = scaleMeasurementList.get(i);
-                    float value = measurementView.getMeasurementValue(measurement);
-
-                    if (value != 0.0f) {
-                        nonZeroScaleMeasurementList.add(measurement);
-                    }
-                }
-
+                ArrayList<ScaleMeasurement> nonZeroScaleMeasurementList = getNonZeroScaleMeasurementsList(measurementView);
                 // check if we have some data left otherwise skip the measurement
                 if (nonZeroScaleMeasurementList.isEmpty()) {
                     continue;
                 }
 
                 // calculate the trendline from the non-zero scale measurement list
-                List<ScaleMeasurement> scaleMeasurementsAsTrendlineList = getScaleMeasurementsAsTrendline(nonZeroScaleMeasurementList);
+                List<ScaleMeasurement> scaleMeasurementsAsTrendlineList = trendlineComputation.processMeasurements(nonZeroScaleMeasurementList);
 
-                for (int i=0; i<scaleMeasurementsAsTrendlineList.size(); i++) {
-                    ScaleMeasurement measurement = scaleMeasurementsAsTrendlineList.get(i);
-                    float value = measurementView.getConvertedMeasurementValue(measurement);
+                final List<Entry> lineEntries = convertMeasurementsToLineEntries(measurementView, scaleMeasurementsAsTrendlineList);
 
-                    Entry entry = new Entry();
-                    entry.setX(convertDateToInt(measurement.getDateTime()));
-                    entry.setY(value);
-                    Object[] extraData = new Object[3];
-                    extraData[0] = measurement;
-                    extraData[1] = (i == 0) ? null : scaleMeasurementsAsTrendlineList.get(i-1);
-                    extraData[2] = measurementView;
-                    entry.setData(extraData);
+                addMeasurementLineTrend(lineDataSets, lineEntries, measurementView, getContext().getString(R.string.label_trend_line));
 
-                    lineEntries.add(entry);
+                // add the future entries
+                if (prefs.getBoolean("trendlineFuture", true)) {
+                    addPredictionLine(lineDataSets, lineEntries, measurementView);
                 }
-
-                addMeasurementLineTrend(lineDataSets, lineEntries, measurementView);
-                addPredictionLine(lineDataSets, lineEntries, measurementView);
             }
         }
     }
 
+    private List<Entry> convertMeasurementsToLineEntries(FloatMeasurementView measurementView, List<ScaleMeasurement> measurementsList) {
+        List<Entry> lineEntries = new ArrayList<>();
+        for (int i = 0; i< measurementsList.size(); i++) {
+            ScaleMeasurement measurement = measurementsList.get(i);
+            float value = measurementView.getConvertedMeasurementValue(measurement);
+
+            Entry entry = new Entry();
+            entry.setX(convertDateToInt(measurement.getDateTime()));
+            entry.setY(value);
+            Object[] extraData = new Object[3];
+            extraData[0] = measurement;
+            extraData[1] = (i == 0) ? null : measurementsList.get(i-1);
+            extraData[2] = measurementView;
+            entry.setData(extraData);
+
+            lineEntries.add(entry);
+        }
+
+        return lineEntries;
+    }
+
     private void addPredictionLine(List<ILineDataSet> lineDataSets, List<Entry> lineEntries, FloatMeasurementView measurementView) {
         if (lineEntries.size() < 2) {
             return;
@@ -605,8 +676,8 @@ public class ChartMeasurementView extends LineChart {
         }
     }
 
-    private void addMeasurementLineTrend(List<ILineDataSet> lineDataSets, List<Entry> lineEntries, FloatMeasurementView measurementView) {
-        LineDataSet measurementLine = new LineDataSet(lineEntries, measurementView.getName().toString() + "-" + getContext().getString(R.string.label_trend_line));
+    private void addMeasurementLineTrend(List<ILineDataSet> lineDataSets, List<Entry> lineEntries, FloatMeasurementView measurementView, String name) {
+        LineDataSet measurementLine = new LineDataSet(lineEntries, measurementView.getName().toString() + "-" + name);
         measurementLine.setLineWidth(1.5f);
         measurementLine.setValueTextSize(10.0f);
         measurementLine.setColor(measurementView.getColor());
@@ -634,5 +705,4 @@ public class ChartMeasurementView extends LineChart {
             }
         }
     }
-
 }

android_app/app/src/main/java/com/health/openscale/gui/preferences/GraphPreferences.java

@@ -19,9 +19,13 @@ import android.os.Bundle;
 import android.view.Menu;
 import android.view.MenuInflater;
 
+import androidx.preference.DropDownPreference;
+import androidx.preference.Preference;
 import androidx.preference.PreferenceFragmentCompat;
+import androidx.preference.SeekBarPreference;
 
 import com.health.openscale.R;
+import com.health.openscale.gui.measurement.ChartMeasurementView;
 
 public class GraphPreferences extends PreferenceFragmentCompat {
     @Override
@@ -29,6 +33,32 @@ public class GraphPreferences extends PreferenceFragmentCompat {
         setPreferencesFromResource(R.xml.graph_preferences, rootKey);
 
         setHasOptionsMenu(true);
+
+        DropDownPreference trendlinePreference = findPreference("trendlineComputationMethod");
+        SeekBarPreference simpleMovingAveragePreference = findPreference("simpleMovingAverageNumDays");
+
+        simpleMovingAveragePreference.setVisible(
+                trendlinePreference.getValue().equals(
+                        ChartMeasurementView.COMPUTATION_METHOD_SIMPLE_MOVING_AVERAGE
+                )
+        );
+
+        trendlinePreference.setOnPreferenceChangeListener(new Preference.OnPreferenceChangeListener() {
+            @Override
+            public boolean onPreferenceChange(Preference preference, Object newValue) {
+                String selectedValue = (String) newValue;
+                boolean simpleMovingAverageEnabled = selectedValue.equals(
+                        ChartMeasurementView.COMPUTATION_METHOD_SIMPLE_MOVING_AVERAGE
+                );
+
+                // hide selector of the number of days when simple moving average is not selected
+                simpleMovingAveragePreference.setVisible(simpleMovingAverageEnabled);
+                // scroll to the bottom to show the new preference to the user
+                getListView().scrollToPosition(getListView().getChildCount());
+
+                return true;
+            }
+        });
     }
 
     @Override

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

@@ -118,4 +118,14 @@
         <item>@string/label_time_period_set_reference_day</item>
         <item>@string/label_time_period_set_custom_range</item>
     </string-array>
+
+    <string-array name="trendline_computation_methods_entries">
+        <item>@string/label_simple_moving_average</item>
+        <item>@string/label_exponentially_smoothed_moving_average</item>
+    </string-array>
+
+    <string-array name="trendline_computation_methods_values">
+        <item>SimpleMovingAverage</item>
+        <item>ExponentiallySmoothedMovingAverage</item>
+    </string-array>
 </resources>

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

@@ -139,6 +139,10 @@
     <string name="Friday">Friday</string>
     <string name="Saturday">Saturday</string>
     <string name="Sunday">Sunday</string>
+    <string name="label_simple_moving_average">Simple Moving Average</string>
+    <string name="label_exponentially_smoothed_moving_average">Exponentially Smoothed Moving Average</string>
+    <string name="label_trendline_computation_method">Trendline computation method</string>
+    <string name="label_trendline_future">Future trend</string>
     <string name="label_bt_device_no_support">device not supported</string>
     <string name="label_exportBackup">Export backup</string>
     <string name="label_importBackup">Import backup</string>
@@ -148,6 +152,7 @@
     <string name="label_initial_weight">Initial weight</string>
     <string name="label_goal_line">Goal line</string>
     <string name="label_trend_line">Trendline</string>
+    <string name="label_simple_moving_average_num_days">Number of days to average over</string>
     <string name="label_prediction">Prediction</string>
     <string name="label_trend">Trend</string>
     <string name="label_help">Help</string>

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

@@ -1,5 +1,6 @@
 <?xml version="1.0" encoding="utf-8"?>
-<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">
+<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto">
     <CheckBoxPreference
         android:defaultValue="true"
         android:key="legendEnable"
@@ -24,10 +25,41 @@
         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="trendLine"
-        android:summaryOff="@string/info_is_not_enable"
-        android:summaryOn="@string/info_is_enable"
-        android:title="@string/label_trend_line" />
+    <PreferenceCategory
+        app:key="trendlineCategory"
+        app:title="@string/label_trend_line">
+
+        <CheckBoxPreference
+            android:defaultValue="false"
+            android:key="trendLine"
+            android:summaryOff="@string/info_is_not_enable"
+            android:summaryOn="@string/info_is_enable"
+            android:title="@string/label_trend_line" />
+        <CheckBoxPreference
+            android:defaultValue="true"
+            android:key="trendlineFuture"
+            android:dependency="trendLine"
+            android:summaryOff="@string/info_is_not_enable"
+            android:summaryOn="@string/info_is_enable"
+            android:title="@string/label_trendline_future" />
+        <DropDownPreference
+            android:id="@+id/trendlineComputationMethodDropdown"
+            android:defaultValue="Exponentially Smoothed Moving Average"
+            android:key="trendlineComputationMethod"
+            android:dependency="trendLine"
+            android:entries="@array/trendline_computation_methods_entries"
+            android:entryValues="@array/trendline_computation_methods_values"
+            app:useSimpleSummaryProvider="true"
+            android:title="@string/label_trendline_computation_method"
+            />
+        <SeekBarPreference
+            android:id="@+id/simpleMovingAverageNumDaysSeekbar"
+            android:defaultValue="7"
+            android:key="simpleMovingAverageNumDays"
+            android:dependency="trendLine"
+            android:max="30"
+            app:min="2"
+            app:showSeekBarValue="true"
+            android:title="@string/label_simple_moving_average_num_days" />
+    </PreferenceCategory>
 </PreferenceScreen>