diff --git a/src/lib/aqdiagram/data/0BUILD b/src/lib/aqdiagram/data/0BUILD
index 232d02a..efad724 100644
--- a/src/lib/aqdiagram/data/0BUILD
+++ b/src/lib/aqdiagram/data/0BUILD
@@ -59,6 +59,7 @@
     <headers dist="true" install="$(pkgincludedir)/data">
       average.h
       accumulate.h
+      negate.h
       floatingavg.h
       date.h
       diff.h
@@ -72,6 +73,7 @@
       $(local/typefiles)
       average.c
       accumulate.c
+      negate.c
       floatingavg.c
       date.c
       diff.c
diff --git a/src/lib/aqdiagram/data/negate.c b/src/lib/aqdiagram/data/negate.c
new file mode 100644
index 0000000..6a7b988
--- /dev/null
+++ b/src/lib/aqdiagram/data/negate.c
@@ -0,0 +1,105 @@
+/****************************************************************************
+ * This file is part of the project AqDiagram.
+ * AqDiagram (c) by 2025 Martin Preuss, all rights reserved.
+ *
+ * The license for this file can be found in the file COPYING which you
+ * should have received along with this file.
+ ****************************************************************************/
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif
+
+#include "./negate.h"
+
+
+
+AQDG_GRAPH_DATAPAIR_LIST *AQDG_Data_NegateY(const AQDG_GRAPH_DATAPAIR_LIST *dpList)
+{
+  if (dpList && AQDG_Graph_DataPair_List_GetCount(dpList)) {
+    AQDG_GRAPH_DATAPAIR_LIST *newList;
+    const AQDG_GRAPH_DATAPAIR *dp;
+
+    newList=AQDG_Graph_DataPair_List_new();
+    dp=AQDG_Graph_DataPair_List_First(dpList);
+    while(dp) {
+      AQDG_GRAPH_DATAPAIR *newDp;
+      double v;
+
+      v=AQDG_Graph_DataPair_GetValueY(dp);
+      newDp=AQDG_Graph_DataPair_dup(dp);
+      AQDG_Graph_DataPair_SetValueY(newDp, -v);
+      AQDG_Graph_DataPair_List_Add(newDp, newList);
+
+      dp=AQDG_Graph_DataPair_List_Next(dp);
+    }
+    return newList;
+  }
+  return NULL;
+}
+
+
+
+AQDG_GRAPH_DATAPAIR_LIST *AQDG_Data_NegateX(const AQDG_GRAPH_DATAPAIR_LIST *dpList)
+{
+  if (dpList && AQDG_Graph_DataPair_List_GetCount(dpList)) {
+    AQDG_GRAPH_DATAPAIR_LIST *newList;
+    const AQDG_GRAPH_DATAPAIR *dp;
+
+    newList=AQDG_Graph_DataPair_List_new();
+    dp=AQDG_Graph_DataPair_List_First(dpList);
+    while(dp) {
+      AQDG_GRAPH_DATAPAIR *newDp;
+      double v;
+
+      v=AQDG_Graph_DataPair_GetValueX(dp);
+      newDp=AQDG_Graph_DataPair_dup(dp);
+      AQDG_Graph_DataPair_SetValueX(newDp, -v);
+      AQDG_Graph_DataPair_List_Add(newDp, newList);
+
+      dp=AQDG_Graph_DataPair_List_Next(dp);
+    }
+    return newList;
+  }
+  return NULL;
+}
+
+
+
+void AQDG_Data_NegateInPlaceY(AQDG_GRAPH_DATAPAIR_LIST *dpList)
+{
+  if (dpList && AQDG_Graph_DataPair_List_GetCount(dpList)) {
+    AQDG_GRAPH_DATAPAIR *dp;
+
+    dp=AQDG_Graph_DataPair_List_First(dpList);
+    while(dp) {
+      double v;
+
+      v=AQDG_Graph_DataPair_GetValueY(dp);
+      AQDG_Graph_DataPair_SetValueY(dp, -v);
+
+      dp=AQDG_Graph_DataPair_List_Next(dp);
+    }
+  }
+}
+
+
+
+void AQDG_Data_NegateInPlaceX(AQDG_GRAPH_DATAPAIR_LIST *dpList)
+{
+  if (dpList && AQDG_Graph_DataPair_List_GetCount(dpList)) {
+    AQDG_GRAPH_DATAPAIR *dp;
+
+    dp=AQDG_Graph_DataPair_List_First(dpList);
+    while(dp) {
+      double v;
+
+      v=AQDG_Graph_DataPair_GetValueX(dp);
+      AQDG_Graph_DataPair_SetValueX(dp, -v);
+
+      dp=AQDG_Graph_DataPair_List_Next(dp);
+    }
+  }
+}
+
+
diff --git a/src/lib/aqdiagram/data/negate.h b/src/lib/aqdiagram/data/negate.h
new file mode 100644
index 0000000..4e96178
--- /dev/null
+++ b/src/lib/aqdiagram/data/negate.h
@@ -0,0 +1,37 @@
+/****************************************************************************
+ * This file is part of the project AqDiagram.
+ * AqDiagram (c) by 2025 Martin Preuss, all rights reserved.
+ *
+ * The license for this file can be found in the file COPYING which you
+ * should have received along with this file.
+ ****************************************************************************/
+
+#ifndef AQDG_DATA_NEGATE_H
+#define AQDG_DATA_NEGATE_H
+
+#include <aqdiagram/graph/datapair.h>
+
+
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+
+
+AQDG_API AQDG_GRAPH_DATAPAIR_LIST *AQDG_Data_NegateY(const AQDG_GRAPH_DATAPAIR_LIST *dpList);
+AQDG_API AQDG_GRAPH_DATAPAIR_LIST *AQDG_Data_NegateX(const AQDG_GRAPH_DATAPAIR_LIST *dpList);
+
+AQDG_API void AQDG_Data_NegateInPlaceY(AQDG_GRAPH_DATAPAIR_LIST *dpList);
+AQDG_API void AQDG_Data_NegateInPlaceX(AQDG_GRAPH_DATAPAIR_LIST *dpList);
+
+
+
+#ifdef __cplusplus
+}
+#endif
+
+
+
+#endif
+