histogram calculation

lib/torque/provider/filterableJson.js

@@ -490,6 +490,47 @@ var Profiler = require('../profiler');
 
     _fetchKeySpan: function() {
       this._setReady(true);
+    },
+
+    getHistogram: function(varName, callback) {
+
+//{"bin":0,"start":1,"end":15.5,"freq":17,"min":1,"max":17},
+      var sql = [
+      'with width as (',
+         'select min({column}) as min,',
+                 'max({column}) as max,',
+                '20 as buckets',
+                'from {table}',
+      '),',
+      '_bw as ( select (max - min)/buckets as bw from width ),',
+      'histogram as (',
+        'select width_bucket({column}, min, max, buckets) as bucket,',
+               'numrange(min({column})::numeric, max({column})::numeric, \'[]\') as range,',
+               'count(*) as freq',
+          'from {table}, width ',
+          //'where trip_time_in_secs between min and max',
+        'group by bucket',
+        'order by bucket',
+      ')',
+      'select bucket*bw as start, (bucket+1)*bw as end, bucket as bin, lower(range) as min, upper(range) as max, freq from histogram, _bw;'
+      ]
+
+
+      var query = format(sql.join('\n'), this.options, {
+        column: this.options.column,
+        table: this.options.table, 
+        filters: this._generateFiltersSQL()
+      });
+
+      var self = this;
+      this.sql(query, function (data) {
+        if (data) {
+          var rows = JSON.parse(data.responseText).rows;
+          callback(null, rows);
+        } else {
+          callback(null);
+        }
+      });
     }
 
   };