Fix single fixation bug and entropy NaN handling

src/main/java/com/github/thed2lab/analysis/DataFilter.java

@@ -35,9 +35,11 @@ static public DataEntry filterByFixations(DataEntry data) {
                 lastValidFixation = data.getRow(row);
             }
         }
-        // Edge case: check last valid fixation is the last line of file or followed by only saccades
-        if (filtered.rowCount() != 0 && lastValidFixation != filtered.getRow(filtered.rowCount()-1)) {
-            filtered.process(lastValidFixation);    // add fixation if it wasn't already added
+        // Edge case: save last fixation if it exists and wasn't already added
+        if (lastValidFixation != null) {
+            if (filtered.rowCount() == 0 || !lastValidFixation.equals(filtered.getRow(filtered.rowCount()-1))) {
+                filtered.process(lastValidFixation);
+            }
         }
 
         return filtered;

src/main/java/com/github/thed2lab/analysis/GazeEntropy.java

@@ -65,16 +65,18 @@ static public LinkedHashMap<String,String> analyze(DataEntry fixations) {
 
         var results = new LinkedHashMap<String,String>();
 
-        results.put(
-            "stationary_entropy", //Output Header
-            String.valueOf(getStationaryEntropy(aoiProbability)) //Output Value
-            );
+        // Return NaN if no fixations/AOIs exist, otherwise calculate entropy
+        double stationaryEntropyValue = aoiProbability.isEmpty()
+            ? Double.NaN
+            : getStationaryEntropy(aoiProbability);
+
+        double transitionEntropyValue = transitionProbability.isEmpty()
+            ? Double.NaN
+            : getTransitionEntropy(aoiProbability, transitionProbability);
+
+        results.put("stationary_entropy", String.valueOf(stationaryEntropyValue));
+        results.put("transition_entropy", String.valueOf(transitionEntropyValue));
 
-        results.put(
-            "transition_entropy", //Output Header
-            String.valueOf(getTransitionEntropy(aoiProbability, transitionProbability)) //Output Value
-            );
-
         return results;
     }