Height transitions go from top down, rather than from bottom up in D3

Question

I\'m making a bar chart with the following code:

svg.selectAll(\".bar\")
    .data(data)
    .enter().append(\"rect\")
    .attr(\"class\", \"bar\")
    .attr(\"         


        

Answer 1

A thing that was counter intuitive and caused me to create some upside down graphs is the svg coordinates x,y start 0,0 at the top left corner, rather than the bottom left corner.

Answer 2

I think the attribute("class", bar) is not required and you can use rangeBand() to calculate width and check your Yaxis scale takes value [height,0] and rest of the code looks fine.

Answer 3

If you inspect the bar elements, you can see that d3 bars are drawn from a the required height to the y position. So you should try as shown below.

svg.selectAll(".bar")
  .data(data)
  .enter().append("rect")
  .attr("class", "bar")
  .attr("x", function(d) {
    return x(d.letter);
  })
  .attr("width", x.rangeBand())
  .attr("height", function(d) {
    return height - y(d.frequency);
  })
  .attr("y", height)
  .transition()
  .duration(500)
  .attr("y", function(d) {
    return y(d.frequency);
  });

Working snippet:

var margin = {
    top: 20,
    right: 20,
    bottom: 30,
    left: 40
  },
  width = 960 - margin.left - margin.right,
  height = 500 - margin.top - margin.bottom;

var x = d3.scale.ordinal()
  .rangeRoundBands([0, width], .1);

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")
  .ticks(10, "%");

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 = [{
  "letter": "A",
  "frequency": 0.08167
}, {
  "letter": "B",
  "frequency": 0.01492
}, {
  "letter": "C",
  "frequency": 0.02782
}, {
  "letter": "D",
  "frequency": 0.04253
}, {
  "letter": "E",
  "frequency": 0.12702
}, {
  "letter": "F",
  "frequency": 0.02288
}, {
  "letter": "G",
  "frequency": 0.02015
}, {
  "letter": "H",
  "frequency": 0.06094
}, {
  "letter": "I",
  "frequency": 0.06966
}, {
  "letter": "J",
  "frequency": 0.00153
}, {
  "letter": "K",
  "frequency": 0.00772
}, {
  "letter": "L",
  "frequency": 0.04025
}, {
  "letter": "M",
  "frequency": 0.02406
}, {
  "letter": "N",
  "frequency": 0.06749
}, {
  "letter": "O",
  "frequency": 0.07507
}, {
  "letter": "P",
  "frequency": 0.01929
}, {
  "letter": "Q",
  "frequency": 0.00095
}, {
  "letter": "R",
  "frequency": 0.05987
}, {
  "letter": "S",
  "frequency": 0.06327
}, {
  "letter": "T",
  "frequency": 0.09056
}, {
  "letter": "U",
  "frequency": 0.02758
}, {
  "letter": "V",
  "frequency": 0.00978
}, {
  "letter": "W",
  "frequency": 0.0236
}, {
  "letter": "X",
  "frequency": 0.0015
}, {
  "letter": "Y",
  "frequency": 0.01974
}, {
  "letter": "Z",
  "frequency": 0.00074
}, {
  "letter": "LICENSE",
  "frequency": 0
}];


x.domain(data.map(function(d) {
  return d.letter;
}));
y.domain([0, d3.max(data, function(d) {
  return d.frequency;
})]);

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")
  .style("text-anchor", "end")
  .text("Frequency");

svg.selectAll(".bar")
  .data(data)
  .enter().append("rect")
  .attr("class", "bar")
  .attr("x", function(d) {
    return x(d.letter);
  })
  .attr("width", x.rangeBand())
  .attr("height", function(d) {
    return height - y(d.frequency);
  })
  .attr("y", height)
  .transition()
  .duration(500)
  .attr("y", function(d) {
    return y(d.frequency);
  });


function type(d) {
  d.frequency = +d.frequency;
  return d;
}

.bar {
  fill: steelblue;
}
.bar:hover {
  fill: brown;
}
.axis {
  font: 10px sans-serif;
}
.axis path,
.axis line {
  fill: none;
  stroke: #000;
  shape-rendering: crispEdges;
}
.x.axis path {
  display: none;
}

<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>

Answer 4

Why is this happening?

The way that this is set up means that you're setting the top of the rect to be at whatever y-value relates to d.frequency, and then defining the bottom to be on the x-axis itself (by subtracting the calculated y-value from the max height). Given that before the transition you're effectively fixing the y-value, then getting the height to transition, what you're actually doing is just moving the bottom of the rect, giving the effect you describe.

How can I fix this?

The simplest fix is to transition both the y-value and the height, in a manner that keeps the bottom of the rect fixed. To do this, before the transition simply set the y attr to be y(0), then after the transition(), set the y attr to be the calculated version, i.e. y(d.frequency). Like so:

svg.selectAll(".bar")
    .data(data)
    .enter().append("rect")
    .attr("class", "bar")
    .attr("x", function(d) {
        return x(d.value) - barWidth / 2;
    })
    .attr("width", barWidth)
    .attr("y", function(d) {
        return y(0);
    })
    .attr("height", 0)
    .transition()
    .attr("y", function(d) {
        return y(d.frequency);
    })
    .attr("height", function(d) {
        return height - y(d.frequency);
    });