Added Some Helpers

MathPad/NSIndexPath+MPAdditions.m

@@ -58,4 +58,29 @@
     return [[self indexPathByRemovingLastIndex] indexPathByAddingIndex:lastIndex];
 }
 
+- (NSIndexPath *)indexPathWithLength:(NSUInteger)length
+{
+    NSIndexPath *indexPath = [[NSIndexPath alloc] init];
+    for (NSUInteger position = 0; position < length; position++) {
+        indexPath = [indexPath indexPathByAddingIndex:[self indexAtPosition:position]];
+    }
+    return indexPath;
+}
+
+- (NSIndexPath *)commonIndexPathWith:(NSIndexPath *)indexPath
+{
+    NSIndexPath *commonPath = [[NSIndexPath alloc] init];
+    NSUInteger length = MIN(self.length, indexPath.length);
+    for (NSUInteger position = 0; position < length; position++) {
+        NSUInteger selfIndex = [self indexAtPosition:position];
+        NSUInteger otherIndex = [indexPath indexAtPosition:position];
+        if (selfIndex == otherIndex) {
+            commonPath = [commonPath indexPathByAddingIndex:selfIndex];
+        } else {
+            break;
+        }
+    }
+    return commonPath;
+}
+
 @end