provide option to display totals on top of each bar

src/traces/bar/layout_attributes.js

@@ -51,5 +51,19 @@ module.exports = {
             'Sets the gap (in plot fraction) between bars of',
             'the same location coordinate.'
         ].join(' ')
-    }
+    },
+    barshowtotal: {
+        valType: 'boolean',
+        dflt: false,
+        role: 'style',
+        editType: 'plot',
+        description: 'Display the total value of each bar.'
+    },
+    totaltemplate: {
+        valType: 'string',
+        dflt: '%{total}',
+        role: 'style',
+        editType: 'plot',
+        description: 'Template to display the total value of each bar.'
+    },
 };

src/traces/bar/layout_defaults.js

@@ -47,4 +47,6 @@ module.exports = function(layoutIn, layoutOut, fullData) {
 
     coerce('bargap', (shouldBeGapless && !gappedAnyway) ? 0 : 0.2);
     coerce('bargroupgap');
+    var showTotal = coerce('barshowtotal');
+    if(showTotal) coerce('totaltemplate');
 };

src/traces/bar/plot.js

@@ -243,6 +243,9 @@ function plot(gd, plotinfo, cdModule, traceLayer, opts, makeOnCompleteCallback)
             }
 
             appendBarText(gd, plotinfo, bar, cd, i, x0, x1, y0, y1, opts, makeOnCompleteCallback);
+            if(fullLayout.barshowtotal) {
+                appendBarTotal(gd, plotinfo, bar, cd, i, x0, x1, y0, y1, opts, makeOnCompleteCallback);
+            }
 
             if(plotinfo.layerClipId) {
                 Drawing.hideOutsideRangePoint(di, bar.select('text'), xa, ya, trace.xcalendar, trace.ycalendar);
@@ -267,7 +270,7 @@ function appendBarText(gd, plotinfo, bar, cd, i, x0, x1, y0, y1, opts, makeOnCom
     var textPosition;
 
     function appendTextNode(bar, text, font) {
-        var textSelection = Lib.ensureSingle(bar, 'text')
+        var textSelection = Lib.ensureSingle(bar, 'text', 'bartext-' + textPosition)
             .text(text)
             .attr({
                 'class': 'bartext bartext-' + textPosition,
@@ -287,7 +290,7 @@ function appendBarText(gd, plotinfo, bar, cd, i, x0, x1, y0, y1, opts, makeOnCom
     var isHorizontal = (trace.orientation === 'h');
 
     var text = getText(fullLayout, cd, i, xa, ya);
-    textPosition = getTextPosition(trace, i);
+    textPosition = fullLayout.barshowtotal ? 'inside' : getTextPosition(trace, i);
 
     // compute text position
     var inStackOrRelativeMode =
@@ -435,6 +438,48 @@ function appendBarText(gd, plotinfo, bar, cd, i, x0, x1, y0, y1, opts, makeOnCom
         .attr('transform', Lib.getTextTransform(transform));
 }
 
+// total for stacked bars
+function appendBarTotal(gd, plotinfo, bar, cd, i, x0, x1, y0, y1, opts, makeOnCompleteCallback) {
+    var fullLayout = gd._fullLayout;
+    // get trace attributes
+    var trace = cd[0].trace;
+    var isHorizontal = (trace.orientation === 'h');
+    var inStackOrRelativeMode =
+        opts.mode === 'stack' ||
+        opts.mode === 'relative';
+    var calcBar = cd[i];
+    var isOutmostBar = !inStackOrRelativeMode || calcBar._outmost;
+
+    if(isOutmostBar) {
+        var layoutFont = fullLayout.font;
+        var font = style.getOutsideTextFont(trace, i, layoutFont);
+        var totalTemplate = fullLayout.totaltemplate;
+        var obj = {total: isHorizontal ? calcBar.x : calcBar.y};
+        var totalText = Lib.texttemplateString(totalTemplate, obj, fullLayout._d2locale, {}, obj, trace._meta || {});
+        var totalSelection = Lib.ensureSingle(bar, 'text', 'bartext-outside')
+            .text(totalText)
+            .attr({
+                'class': 'bartext bartext-outside',
+                'text-anchor': 'middle',
+                // prohibit tex interpretation until we can handle
+                // tex and regular text together
+                'data-notex': 1
+            })
+            .call(Drawing.font, font)
+            .call(svgTextUtils.convertToTspans, gd);
+
+        var textBB = Drawing.bBox(totalSelection.node());
+        var transform = toMoveOutsideBar(x0, x1, y0, y1, textBB, {
+            isHorizontal: isHorizontal,
+            constrained: false,
+            angle: trace.textangle
+        });
+
+        transition(totalSelection, fullLayout, opts, makeOnCompleteCallback)
+            .attr('transform', Lib.getTextTransform(transform));
+    }
+}
+
 function getRotateFromAngle(angle) {
     return (angle === 'auto') ? 0 : angle;
 }

test/image/mocks/bar_stackrelative_negative_total.json

@@ -0,0 +1,34 @@
+{
+    "data":[
+        {
+            "name":"Col1",
+            "y":["-1","2","3","4","5"],
+            "x":["1","2","3","4","5"],
+            "type":"bar"
+        },
+        {
+            "name":"Col2",
+            "y":["2","3","4","-3","2"],
+            "x":["1","2","3","4","5"],
+            "type":"bar"
+        },
+        {
+            "name":"Col3",
+            "y":["5","4","3","-2","1"],
+            "x":["1","2","3","4","5"],
+            "type":"bar"
+        },
+        {
+            "name":"Col4",
+            "y":["-3","0","1","0","-3"],
+            "x":["1","2","3","4","5"],
+            "type":"bar"
+        }
+    ],
+    "layout":{
+        "height":400,
+        "width":400,
+        "barshowtotal": true,
+        "barmode":"relative"
+    }
+}