Suppose I have this CSV file Day,What 2013-10-27,Apple 2013-10-27,Cake 2013-10-27,Apple 2013-10-28,Apple 2013-10-28,Apple 2013-10-28,Blueberry 2013-10-28,Orange I would like to drawn with D3.js a time-series graph. All I need to do is to display the sum of the number of rows for each day. As an example, the 27 of November should have 3 as value, the 28th should have 4. Is there a way I can archive it? I've been trying to create a new dataset out of the CSV one with no positive results. var dataset; d3.csv("data.csv", function(d) { return { Day: new Date(d.Day), What: d.What }; }, function(error, rows) { dataset = rows; // I SUPPOSE THE FUNCTION THAT GENERATE THE NEW DATASET SHOULD GO THERE });