Smooth transition on updating paths in d3 v5

Question

I'm trying to build a d3 line chart which updates the chart data on each click. Here's my progress so far:

 var n = 10, random = d3.randomNormal(0, .2), data = d3.range(n).map(random); var svg = d3.select("svg"), margin = { top: 20, right: 20, bottom: 20, left: 40 }, width = +svg.attr("width") - margin.left - margin.right, height = +svg.attr("height") - margin.top - margin.bottom, g = svg.append("g").attr("transform", "translate(" + margin.left + "," + margin.top + ")"); var x = d3.scaleLinear() .domain([0, n - 1]) .range([0, width]); var y = d3.scaleLinear() .domain([-1, 1]) .range([height, 0]); var line = d3.line() .x(function(d, i) { return x(i); }) .y(function(d, i) { return y(d); }); g.append("defs").append("clipPath") .attr("id", "clip") .append("rect") .attr("width", width) .attr("height", height); g.append("g") .attr("class", "axis axis--x") .attr("transform", "translate(0," + y(0) + ")") .call(d3.axisBottom(x)); g.append("g") .attr("class", "axis axis--y") .call(d3.axisLeft(y)); g.append("g") .attr("clip-path", "url(#clip)") .append("path") .datum(data) .attr("class", "line") .attr('d', line) function tick() { // Push a new data point onto the back. data.push(random()); // Redraw the line. d3.select(".line") .attr("d", line) .attr("transform", null) .transition() .duration(300) // Slide it to the left. d3.select(".line") .attr("transform", "translate(" + x(-1) + ",0)") .transition() .duration(300) // Pop the old data point off the front. data.shift(); } d3.select("#translate") .on("click", tick) 

 .line { fill: none; stroke: #000; stroke-width: 1.5px; } 

 <script src="https://d3js.org/d3.v5.min.js"></script> <button id="translate">Translate</button> <svg width="960" height="500"></svg> 

Currently, the chart updates instantly without any transition (even though i have added transition in update function). Whats am i doing wrong here?

I want to achieve something like this https://bl.ocks.org/mbostock/1642874 , but on "click" rather than on "start" event.

Answer 1

You aren't transitioning anything:

d3.select(".line")
  .attr("...")
  .transition()
  .duration()

This doesn't specify that you are transitioning anything. The first two lines return the selection, the second two lines return a transition - you need to use .attr() on a transition to actually transition something. If .attr() is used on a selection, it simply updates that attribute. So, you need to use this pattern:

d3.select(".line")
  .transition()
  .duration()
  .attr("...")  // attribute to be transitioned

Or:

d3.select(".line")
  .transition()
  .attr("...")  // attribute to be transitioned
  .duration()

Also, you don't need to transition twice, add the new data and then shift the graph:

// Redraw the line.
d3.select(".line")
  .attr("d", line)
  .attr("transform", null)
  .transition()
  .attr("transform", "translate(" + x(-1) + ",0)")
  .duration(300)

Snippet:

 var n = 10, random = d3.randomNormal(0, .2), data = d3.range(n).map(random); var svg = d3.select("svg"), margin = { top: 20, right: 20, bottom: 20, left: 40 }, width = +svg.attr("width") - margin.left - margin.right, height = +svg.attr("height") - margin.top - margin.bottom, g = svg.append("g").attr("transform", "translate(" + margin.left + "," + margin.top + ")"); var x = d3.scaleLinear() .domain([0, n - 1]) .range([0, width]); var y = d3.scaleLinear() .domain([-1, 1]) .range([height, 0]); var line = d3.line() .x(function(d, i) { return x(i); }) .y(function(d, i) { return y(d); }); g.append("defs").append("clipPath") .attr("id", "clip") .append("rect") .attr("width", width) .attr("height", height); g.append("g") .attr("class", "axis axis--x") .attr("transform", "translate(0," + y(0) + ")") .call(d3.axisBottom(x)); g.append("g") .attr("class", "axis axis--y") .call(d3.axisLeft(y)); g.append("g") .attr("clip-path", "url(#clip)") .append("path") .datum(data) .attr("class", "line") .attr('d', line) function tick() { // Push a new data point onto the back. data.push(random()); // Redraw the line. d3.select(".line") .attr("d", line) .attr("transform", null) .transition() .attr("transform", "translate(" + x(-1) + ",0)") .duration(300) // Pop the old data point off the front. data.shift(); } d3.select("#translate") .on("click", tick) 

 .line { fill: none; stroke: #000; stroke-width: 1.5px; } 

 <script src="https://d3js.org/d3.v5.min.js"></script> <button id="translate">Translate</button> <svg width="960" height="500"></svg>