How to display the size as tooltip in a d3.js graph?

@domenico 

To display the size as a tooltip in a d3.js graph, you can use the d3-tip library. Here's how you can do it:

1. First, include the d3-tip library in your HTML file. You can do this by adding the following script tag:

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<script src="https://cdnjs.cloudflare.com/ajax/libs/d3-tip/0.9.1/d3-tip.min.js"></script>

1. Next, create a tooltip function using d3.tip() and set the content of the tooltip to display the size of the data point. You can customize the tooltip content as needed.

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var tip = d3.tip()
  .attr('class', 'd3-tip')
  .offset([-10, 0])
  .html(function(d) {
    return "<strong>Size:</strong> <span style='color:red'>" + d.size + "</span>";
  });

1. Append the tooltip to your SVG element:

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svg.call(tip);

1. Add the tooltip event listeners to display the tooltip on mouseover and hide it on mouseout. You can do this by adding the following code to your data binding:

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node.on('mouseover', tip.show)
    .on('mouseout', tip.hide);

1. Finally, you can style the tooltip using CSS. You can customize the tooltip styles by targeting the .d3-tip class in your CSS file.

That's it! Now when you hover over a data point in your d3.js graph, the tooltip will display the size of the data point.