JSON Group by count, output to key value pair json result

Following is the JSON and need to manipulate it in format to groupBy.

var rows = [ { 'createdDate': '3/11/2016', 'createdBy': 'Bob' }, { 'createdDate': '3/12/2016', 'createdBy': 'Megan' }, { 'createdDate': '3/12/2016', 'createdBy': 'Bob' }, { 'createdDate': '3/13/2016', 'createdBy': 'Sam' }, { 'createdDate': '3/11/2016', 'createdBy': 'Bob' }, ]; var occurences = rows.reduce(function (r, row) { r[row.createdBy] = ++r[row.createdBy] || 1; return r; }, {}); var result = Object.keys(occurences).map(function (key) { return { key: key, value: occurences[key] }; }); console.log(result);