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D3: get closest value from ordinal axis when hovering mouse

In my D3 diagram, I am trying to create a mouseover effect, as in this example: http://bl.ocks.org/mbostock/3902569

In this example, the author uses the bisector function, which, as I understand it, is supported only for linear scales. The problem is that in my diagram I have an x-axis with different, discrete rangePoint tuples. So, if this looks like the situation below (m = mouse position), I want to get the pixel position of the nearest x, which in this example will be x2.

m | x1----------x2----------x3

Is there any way to do this?

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1 answer

Using your related example, we quickly implement the mousemove function for ordinal scale:

 var tickPos = x.range(); function mousemove(d){ var m = d3.mouse(this), lowDiff = 1e99, xI = null; // if you have a large number of ticks // this search could be optimized for (var i = 0; i < tickPos.length; i++){ var diff = Math.abs(m[0] - tickPos[i]); if (diff < lowDiff){ lowDiff = diff; xI = i; } } focus .select('text') .text(ticks[xI]); focus .attr("transform","translate(" + tickPos[xI] + "," + y(data[xI].y) + ")"); }

Full code:

 <!DOCTYPE html> <meta charset="utf-8"> <style> body { font: 10px sans-serif; } .axis path, .axis line { fill: none; stroke: #000; shape-rendering: crispEdges; } .line { fill: none; stroke: steelblue; stroke-width: 1.5px; } .overlay { fill: none; pointer-events: all; } .focus circle { fill: none; stroke: steelblue; } </style> <body> <script src="//d3js.org/d3.v3.min.js"></script> <script> var margin = { top: 20, right: 20, bottom: 30, left: 50 }, width = 960 - margin.left - margin.right, height = 500 - margin.top - margin.bottom; var x = d3.scale.ordinal() .rangeRoundPoints([0, width]); var y = d3.scale.linear() .range([height, 0]); var xAxis = d3.svg.axis() .scale(x) .orient("bottom"); var yAxis = d3.svg.axis() .scale(y) .orient("left"); var line = d3.svg.line() .x(function(d) { return x(dx); }) .y(function(d) { return y(dy); }); var svg = d3.select("body").append("svg") .attr("width", width + margin.left + margin.right) .attr("height", height + margin.top + margin.bottom) .append("g") .attr("transform", "translate(" + margin.left + "," + margin.top + ")"); var data = [{ x: 'A', y: Math.random() * 10 }, { x: 'B', y: Math.random() * 10 }, { x: 'C', y: Math.random() * 10 }, { x: 'D', y: Math.random() * 10 }, { x: 'E', y: Math.random() * 10 }, { x: 'F', y: Math.random() * 10 }, { x: 'G', y: Math.random() * 10 }, { x: 'H', y: Math.random() * 10 }, { x: 'I', y: Math.random() * 10 }, { x: 'J', y: Math.random() * 10 }]; var ticks = data.map(function(d) { return dx }); x.domain(ticks); y.domain(d3.extent(data, function(d) { return dy; })); svg.append("g") .attr("class", "x axis") .attr("transform", "translate(0," + height + ")") .call(xAxis); svg.append("g") .attr("class", "y axis") .call(yAxis) .append("text") .attr("transform", "rotate(-90)") .attr("y", 6) .attr("dy", ".71em"); svg.append("path") .datum(data) .attr("class", "line") .attr("d", line); var focus = svg.append("g") .attr("class", "focus") .style("display", "none"); focus.append("circle") .attr("r", 4.5); focus.append("text") .attr("x", 9) .attr("dy", ".35em") .style('') svg.append("rect") .attr("class", "overlay") .attr("width", width) .attr("height", height) .on("mouseover", function() { focus.style("display", null); }) .on("mouseout", function() { focus.style("display", "none"); }) .on("mousemove", mousemove); var tickPos = x.range(); function mousemove(d){ var m = d3.mouse(this), lowDiff = 1e99, xI = null; for (var i = 0; i < tickPos.length; i++){ var diff = Math.abs(m[0] - tickPos[i]); if (diff < lowDiff){ lowDiff = diff; xI = i; } } focus .select('text') .text(ticks[xI]); focus .attr("transform","translate(" + tickPos[xI] + "," + y(data[xI].y) + ")"); } </script>
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Source: https://habr.com/ru/post/1237883/

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