diff --git a/src/DataFilter.cpp b/src/DataFilter.cpp
index 773568baf..433394983 100644
--- a/src/DataFilter.cpp
+++ b/src/DataFilter.cpp
@@ -143,6 +143,9 @@ Leaf::isDynamic(Leaf *leaf)
 
     case Leaf::Logical  :
                     if (leaf->op == 0) return leaf->isDynamic(leaf->lvalue.l);
+    case Leaf::UnaryOperation :
+                    return leaf->isDynamic(leaf->lvalue.l);
+                    break;
     case Leaf::Operation :
     case Leaf::BinaryOperation :
                     return leaf->isDynamic(leaf->lvalue.l) || leaf->isDynamic(leaf->rvalue.l);
@@ -262,6 +265,10 @@ void Leaf::color(Leaf *leaf, QTextDocument *document)
                     return;
                     break;
 
+    case Leaf::UnaryOperation : 
+                    leaf->color(leaf->lvalue.l, document);
+                    return;
+                    break;
     case Leaf::BinaryOperation : 
                     leaf->color(leaf->lvalue.l, document);
                     leaf->color(leaf->rvalue.l, document);
@@ -338,6 +345,9 @@ void Leaf::print(Leaf *leaf, int level)
                     leaf->print(leaf->lvalue.l, level+1);
                     leaf->print(leaf->rvalue.l, level+1);
                     break;
+    case Leaf::UnaryOperation : qDebug()<<"uop"<<leaf->op;
+                    leaf->print(leaf->lvalue.l, level+1);
+                    break;
     case Leaf::BinaryOperation : qDebug()<<"bop"<<leaf->op;
                     leaf->print(leaf->lvalue.l, level+1);
                     leaf->print(leaf->rvalue.l, level+1);
@@ -414,6 +424,7 @@ bool Leaf::isNumber(DataFilter *df, Leaf *leaf)
         break;
     case Leaf::Logical  : return true; // not possible!
     case Leaf::Operation : return true;
+    case Leaf::UnaryOperation : return true;
     case Leaf::BinaryOperation : return true;
     case Leaf::Function : return true;
     case Leaf::Vector :
@@ -594,6 +605,14 @@ void Leaf::validateFilter(DataFilter *df, Leaf *leaf)
         }
         break;
 
+    case Leaf::UnaryOperation :
+        { // only 1 at present, unary minus return the value * -1
+            if (!Leaf::isNumber(df, leaf->lvalue.l)) {
+                DataFiltererrors << QString(QObject::tr("unary negation on a string!"));
+                leaf->inerror = true;
+            }
+        }
+        break;
     case Leaf::BinaryOperation  :
     case Leaf::Operation  :
         {
@@ -1266,6 +1285,18 @@ Result Leaf::eval(Context *context, DataFilter *df, Leaf *leaf, RideItem *m)
     }
     break;
 
+    //
+    // UNARY EXPRESSION
+    //
+
+    case Leaf::UnaryOperation :
+    {
+        // get result
+        Result lhs = eval(context, df, leaf->lvalue.l, m);
+        return Result(lhs.number * -1);
+    }
+    break;
+
     //
     // BINARY EXPRESSION
     //
diff --git a/src/DataFilter.h b/src/DataFilter.h
index 8e23cfcee..1eedfceee 100644
--- a/src/DataFilter.h
+++ b/src/DataFilter.h
@@ -66,7 +66,7 @@ class Leaf {
         void clear(Leaf*);
 
         enum { none, Float, Integer, String, Symbol, 
-               Logical, Operation, BinaryOperation, 
+               Logical, Operation, BinaryOperation, UnaryOperation,
                Function, Conditional, Vector,
                Parameters } type;
 
diff --git a/src/DataFilter.l b/src/DataFilter.l
index 6dafeb981..414ce0b62 100644
--- a/src/DataFilter.l
+++ b/src/DataFilter.l
@@ -69,9 +69,9 @@ int DataFiltercolumn = 1;
 [Oo][Rr]                                    DataFilterlval.op = OR; return OR;
 
 
-[-+]?[0-9]+                                 return DF_INTEGER;
-[-+]?[0-9]+e-[0-9]+                         return DF_FLOAT;
-[-+]?[0-9]+\.[-e0-9]*                       return DF_FLOAT;
+[0-9]+                                 return DF_INTEGER;
+[0-9]+e-[0-9]+                         return DF_FLOAT;
+[0-9]+\.[-e0-9]*                       return DF_FLOAT;
 \"([^\"]|\\\")*\"                           return DF_STRING;  /* contains non-quotes or escaped-quotes */
 
 
diff --git a/src/DataFilter.y b/src/DataFilter.y
index 19a74c310..dc4facfb3 100644
--- a/src/DataFilter.y
+++ b/src/DataFilter.y
@@ -135,7 +135,12 @@ expr : expr SUBTRACT expr              { $$ = new Leaf(@1.first_column, @3.last_
                                       $$->lvalue.l = $1;
                                       $$->op = $2;
                                       $$->rvalue.l = $3; }
-
+      | SUBTRACT expr %prec MULTIPLY { $$ = new Leaf(@1.first_column, @2.last_column);
+                                      $$->type = Leaf::UnaryOperation;
+                                      $$->lvalue.l = $2;
+                                      $$->op = $1;
+                                      $$->rvalue.l = NULL; 
+                                     }
       | expr '?' expr ':' expr      { $$ = new Leaf(@1.first_column, @5.last_column);
                                     $$->type = Leaf::Conditional;
                                     $$->op = 0; // unused