3 files changed, 63 insertions, 33 deletions

diff --git a/src/web/api/formatters/value/README.md b/src/web/api/formatters/value/README.md
new file mode 100644
index 000000000..3599a836e
--- /dev/null
+++ b/src/web/api/formatters/value/README.md
@@ -0,0 +1,28 @@
+<!--
+title: "Value formatter"
+custom_edit_url: https://github.com/netdata/netdata/edit/master/src/web/api/formatters/value/README.md
+sidebar_label: "Value formatter"
+learn_status: "Published"
+learn_topic_type: "References"
+learn_rel_path: "Developers/Web/Api/Formatters"
+-->
+
+# Value formatter
+
+The Value formatter presents [results of database queries](https://github.com/netdata/netdata/blob/master/src/web/api/queries/README.md) as a single value.
+
+To calculate the single value to be returned, it sums the values of all dimensions.
+
+The Value formatter respects the following API `&options=`:
+
+| option    | supported | description |
+|:----:     |:-------:  |:----------  |
+| `percent` | yes       | to replace all values with their percentage over the row total|
+| `abs`     | yes       | to turn all values positive, before using them |
+| `min2max` | yes       | to return the delta from the minimum value to the maximum value (across dimensions)|
+
+The Value formatter is not exposed by the API by itself.
+Instead it is used by the [`ssv`](https://github.com/netdata/netdata/blob/master/src/web/api/formatters/ssv/README.md) formatter
+and [health monitoring queries](https://github.com/netdata/netdata/blob/master/src/health/README.md).
+
+
diff --git a/web/api/formatters/value/value.c b/src/web/api/formatters/value/value.c
index 1d07f62f6..0ec1b1265 100644
--- a/web/api/formatters/value/value.c
+++ b/src/web/api/formatters/value/value.c
@@ -2,7 +2,6 @@
 
 #include "value.h"
 
-
 inline NETDATA_DOUBLE rrdr2value(RRDR *r, long i, RRDR_OPTIONS options, int *all_values_are_null, NETDATA_DOUBLE *anomaly_rate) {
     size_t c;
 
@@ -10,61 +9,64 @@ inline NETDATA_DOUBLE rrdr2value(RRDR *r, long i, RRDR_OPTIONS options, int *all
     RRDR_VALUE_FLAGS *co = &r->o[ i * r->d ];
     NETDATA_DOUBLE *ar = &r->ar[ i * r->d ];
 
-    NETDATA_DOUBLE sum = 0, min = 0, max = 0, v;
-    int all_null = 1, init = 1;
+    NETDATA_DOUBLE sum = 0, min = NAN, max = NAN, v = NAN;
+    size_t dims = 0;
 
     NETDATA_DOUBLE total_anomaly_rate = 0;
 
     // for each dimension
     for (c = 0; c < r->d ; c++) {
-        if(!rrdr_dimension_should_be_exposed(r->od[c], options))
+        if(unlikely(!rrdr_dimension_should_be_exposed(r->od[c], options)))
+            continue;
+
+        if(unlikely((co[c] & RRDR_VALUE_EMPTY)))
             continue;
 
         NETDATA_DOUBLE n = cn[c];
 
-        if(unlikely(init)) {
-            if(n > 0) {
-                min = 0;
-                max = n;
-            }
-            else {
-                min = n;
-                max = 0;
-            }
-            init = 0;
-        }
+        if(unlikely(!dims))
+            min = max = n;
 
-        if(likely(!(co[c] & RRDR_VALUE_EMPTY))) {
-            all_null = 0;
-            sum += n;
-        }
+        sum += n;
 
-        if(n < min) min = n;
-        if(n > max) max = n;
+        if (n < min) min = n;
+        if (n > max) max = n;
 
         total_anomaly_rate += ar[c];
-    }
 
-    if(anomaly_rate) {
-        if(!r->d) *anomaly_rate = 0;
-        else *anomaly_rate = total_anomaly_rate / (NETDATA_DOUBLE)r->d;
+        dims++;
     }
 
-    if(unlikely(all_null)) {
-        if(likely(all_values_are_null))
+    if(!dims) {
+        if(anomaly_rate)
+            *anomaly_rate = 0;
+
+        if(all_values_are_null)
             *all_values_are_null = 1;
-        return 0;
-    }
-    else {
-        if(likely(all_values_are_null))
-            *all_values_are_null = 0;
+
+        return (options & RRDR_OPTION_NULL2ZERO) ? 0 : NAN;
     }
 
-    if(options & RRDR_OPTION_MIN2MAX)
+    if(anomaly_rate)
+        *anomaly_rate = total_anomaly_rate / (NETDATA_DOUBLE)dims;
+
+    if(all_values_are_null)
+        *all_values_are_null = 0;
+
+    if(options & RRDR_OPTION_DIMS_MIN2MAX)
         v = max - min;
+    else if(options & RRDR_OPTION_DIMS_AVERAGE)
+        v = sum / (NETDATA_DOUBLE)dims;
+    else if(options & RRDR_OPTION_DIMS_MIN)
+        v = min;
+    else if(options & RRDR_OPTION_DIMS_MAX)
+        v = max;
     else
         v = sum;
 
+    if((options & RRDR_OPTION_NULL2ZERO) && (isnan(v) || isinf(v)))
+        v = 0;
+
     return v;
 }
 
diff --git a/web/api/formatters/value/value.h b/src/web/api/formatters/value/value.h
index 072ca14f8..072ca14f8 100644
--- a/web/api/formatters/value/value.h
+++ b/src/web/api/formatters/value/value.h