diff --git a/pdb-utils/src/main/java/org/lucares/utils/MiniMap.java b/pdb-utils/src/main/java/org/lucares/utils/MiniMap.java
index ea99955..9778b25 100644
--- a/pdb-utils/src/main/java/org/lucares/utils/MiniMap.java
+++ b/pdb-utils/src/main/java/org/lucares/utils/MiniMap.java
@@ -15,18 +15,16 @@ public class MiniMap<K, V> {
 	private static final Object[] EMPTY_ARRAY = new Object[0];
 	private static final MiniMap<?,?> EMPTY_MAP = new MiniMap<>();
 	
-	private Object[] keys;
-	private Object[] values;
+	// keys are on even indices (0,2,4,...) and values on uneven (1,3,5,...)
+	private Object[] keysValues;
 
 
 	public MiniMap() {
-		keys = EMPTY_ARRAY;
-		values = EMPTY_ARRAY;
+		keysValues = EMPTY_ARRAY;
 	}
 	
 	public MiniMap(final MiniMap<K, V> miniMap){
-		keys = miniMap.keys.clone();
-		values = miniMap.values.clone();
+		keysValues = miniMap.keysValues.clone();
 	}
 
 	@SuppressWarnings("unchecked")
@@ -35,7 +33,7 @@ public class MiniMap<K, V> {
     }
 	
 	public int size() {
-		return keys.length;
+		return keysValues.length / 2;
 	}
 
 	public boolean isEmpty() {
@@ -49,10 +47,11 @@ public class MiniMap<K, V> {
 	@SuppressWarnings("unchecked")
 	public V get(Object key) {
 
-		for (int i = 0; i < keys.length; i++) {
-			Object object = keys[i];
+		final int size = size();
+		for (int i = 0; i < size; i++) {
+			Object object = keysValues[2*i];
 			if (Objects.equals(key, object)) {
-				return (V) values[i];
+				return (V) keysValues[2*i+1];
 			}
 		}
 		return null;
@@ -63,25 +62,23 @@ public class MiniMap<K, V> {
 		V oldValue = get(key);
 
 		if (oldValue != null) {
-			for (int i = 0; i < keys.length; i++) {
-				Object object = keys[i];
+			final int size = size();
+			for (int i = 0; i < size; i++) {
+				Object object = keysValues[2*i];
 				if (Objects.equals(key, object)) {
-					values[i] = value;
+					keysValues[2*i+1] = value;
 					break;
 				}
 			}
 		} else {
-			final Object[] newKeys = new Object[keys.length + 1];
-			System.arraycopy(keys, 0, newKeys, 0, keys.length);
+			final Object[] newKeysValues = new Object[keysValues.length + 2];
+			System.arraycopy(keysValues, 0, newKeysValues, 0, keysValues.length);
 
-			final Object[] newValues = new Object[values.length + 1];
-			System.arraycopy(values, 0, newValues, 0, values.length);
 
-			newKeys[newKeys.length - 1] = key;
-			newValues[newValues.length - 1] = value;
+			newKeysValues[newKeysValues.length - 2] = key;
+			newKeysValues[newKeysValues.length - 1] = value;
 
-			keys = newKeys;
-			values = newValues;
+			keysValues = newKeysValues;
 		}
 
 		return oldValue;
@@ -94,26 +91,28 @@ public class MiniMap<K, V> {
 	}
 
 	public void clear() {
-		keys = EMPTY_ARRAY;
-		values = EMPTY_ARRAY;
+		keysValues = EMPTY_ARRAY;
 	}
 
 	@SuppressWarnings("unchecked")
 	public Set<K> keySet() {
-		final Set<K> result = new HashSet<>(keys.length);
+		final Set<K> result = new HashSet<>(size());
 
-		for (Object k : keys) {
-			result.add((K) k);
+		final int size = size();
+		for (int i = 0; i < size; i++) {
+			K k = (K) keysValues[2*i];
+			result.add(k);
 		}
 		return result;
 	}
 
 	@SuppressWarnings("unchecked")
 	public Set<V> values() {
-		final Set<V> result = new HashSet<>(values.length);
-
-		for (Object v : values) {
-			result.add((V) v);
+		final Set<V> result = new HashSet<>(size());
+		final int size = size();
+		for (int i = 0; i < size; i++) {
+			V v = (V) keysValues[2*i+1];
+			result.add(v);
 		}
 		return result;
 	}
@@ -122,8 +121,7 @@ public class MiniMap<K, V> {
 	public int hashCode() {
 		final int prime = 31;
 		int result = 1;
-		result = prime * result + Arrays.hashCode(keys);
-		result = prime * result + Arrays.hashCode(values);
+		result = prime * result + Arrays.hashCode(keysValues);
 		return result;
 	}
 
@@ -137,9 +135,7 @@ public class MiniMap<K, V> {
 		if (getClass() != obj.getClass())
 			return false;
 		MiniMap other = (MiniMap) obj;
-		if (!Arrays.equals(keys, other.keys))
-			return false;
-		if (!Arrays.equals(values, other.values))
+		if (!Arrays.equals(keysValues, other.keysValues))
 			return false;
 		return true;
 	}