singlestat: with table data, support string values

If the selected table column is string then show that in the singlestat

public/app/plugins/panel/singlestat/module.ts

@@ -174,10 +174,16 @@ class SingleStatCtrl extends MetricsPanelCtrl {
     const datapoint = tableData[0][0];
     data.value = datapoint[this.panel.tableColumn];
 
-    var decimalInfo = this.getDecimalsForValue(data.value);
-    var formatFunc = kbn.valueFormats[this.panel.format];
-    data.valueFormatted = formatFunc(datapoint[this.panel.tableColumn], decimalInfo.decimals, decimalInfo.scaledDecimals);
-    data.valueRounded = kbn.roundValue(data.value, this.panel.decimals || 0);
+    if (_.isString(data.value)) {
+      data.valueFormatted = _.escape(data.value);
+      data.value = 0;
+      data.valueRounded = 0;
+    } else {
+      const decimalInfo = this.getDecimalsForValue(data.value);
+      const formatFunc = kbn.valueFormats[this.panel.format];
+      data.valueFormatted = formatFunc(datapoint[this.panel.tableColumn], decimalInfo.decimals, decimalInfo.scaledDecimals);
+      data.valueRounded = kbn.roundValue(data.value, this.panel.decimals || 0);
+    }
 
     this.setValueMapping(data);
   }

public/app/plugins/panel/singlestat/specs/singlestat_specs.ts

@@ -242,6 +242,18 @@ describe('SingleStatCtrl', function() {
         expect(ctx.data.valueFormatted).to.be('NOT OK');
       });
     });
+
+    singleStatScenario('When value is string', function(ctx) {
+      ctx.setup(function() {
+        ctx.data = tableData;
+        ctx.data[0].rows[0] = [1492759673649,'ignore1', 65, 'ignore2'];
+        ctx.ctrl.panel.tableColumn = 'test1';
+      });
+
+      it('Should replace value with text NOT OK', function() {
+        expect(ctx.data.valueFormatted).to.be('ignore1');
+      });
+    });
   });
 });