[Solved]-NVD3 Sparkline not rendering correctly from CSV file-d3.js

The problem was that the y values were strings. I changed

monthlyData.push({x: data[i].Month, y: data[i].Data});

to

monthlyData.push({x: data[i].Month, y: +data[i].Data});

so that the y value becomes a number. Here's the updated version.