CODEWITHSUNDEEP
javascriptcsvd3.js
basedian
basedian

Reputation: 317

D3.js Cannot read property 'length' of undefined

I'm pretty new to d3.js and to web too. I wanted to ue a csv file to plot a line graph but I got some errors I can't really fix:

enter image description here

Here is the code:

body,html{
	margin: 0;
	padding: 0;
	font-family: "Arial", sans-serif;
	font-size: 0.95em;
	text-align: center;
}
#chart{
	background-color: #F5F2EB;
	border: 1px solid #CCC;
}
.bar{
	fill: purple;
	shape-rendering: crispEdges;
}
.bar-label{
	fill: black;
	text-anchor: middle;
	font-size: 18px;
}
.axis path,
.axis line{
	fill: none;
	stroke: #000;
	shape-rendering: crispEdges;
}
.gridline path,
.gridline line{
	fill: none;
	stroke: #ccc;
	shape-rendering: crispEdges;
}
<script src="https://cdnjs.cloudflare.com/ajax/libs/d3/3.4.11/d3.min.js"></script>
<!DOCTYPE html>
<html lang="en">
<head>
	<meta charset="UTF-8">
	<title>Learning D3</title>
	<link rel="stylesheet" href="main.css">
	<script  type="text/javascript" src="d3.min.js"></script>
</head>
<body>
<!--Place all DOM elements here -->
<script>

var data= [
	d3.csv("refugee_data.csv", function(d) {
  return {
    /*year: new Date(+d.Year, 0, 1), // convert "Year" column to Date
    make: d.Make,
    model: d.Model,
    length: +d.Length // convert "Length" column to number*/
		date: d.Year + "/" +d.Month,
		origin: d.Origin,
		asylum: d.Asylum,
		value: +d.Value
  };
}, function(error, rows) {
  console.log(rows);
})
];

var w = 800;
var h = 450;
var margin = {
	top: 58,
	bottom: 100,
	left: 80,
	right: 40
};
var width = w - margin.left - margin.right;
var height = h - margin.top - margin.bottom;

var svg = d3.select("body").append("svg")
			.attr("id", "chart")
			.attr("width", w)
			.attr("height", h);
var dateParser = d3.time.format("%Y/%B").parse;
var x = d3.time.scale()
		 .domain(d3.extent(data, function(d){
			var date = dateParser(d.date);
			return date;
		}))
		.range([0,width]);

var y = d3.scale.linear()
		.domain([0, d3.max(data, function(d){
			return d.value;
		})])
		.range([height,0]);

function plot(params){
		//enter()
		this.selectAll(".point")
				.data(params.data)
				.enter()
					.append("circle")
					.classed("point", true)
					.attr("r", 2);
		//Update
		this.selectAll(".point")
		.attr("cx", function(d){
			var date = dateParser(d.date);
			return x(date);
		})
		.attr("cy", function(d){
			return y(d.value);
		})

		//Exit()
		this.selectAll(".point")
		.data(params.data)
		.exit()
		.remove();
}
plot.call(chart, {
	data: data
})
</script>
</body>
</html>

And this ist my a part of my csv, pretty basic so I don't get why it does not work.

Asylum,Origin,Year,Month,Value

Germany,Afghanistan,2014,January,981 Germany,Afghanistan,2014,February,781 Germany,Afghanistan,2014,March,675 Germany,Afghanistan,2014,April,673 Germany,Afghanistan,2014,May,523 Germany,Afghanistan,2014,June,621 Germany,Afghanistan,2014,July,752 Germany,Afghanistan,2014,August,743 Germany,Afghanistan,2014,September,922

I assume it is a really stupid mistake can you please help me out?

Upvotes: 2

Views: 13648

Answers (1)

Luke Woodward
Luke Woodward

Reputation: 64969

Your mistake is assuming that calling d3.csv(...) returns your CSV data.

d3.csv makes an AJAX call to load your data and then calls a callback function when that data has been loaded. Your code continues running while the data loads in the background. When you write var data = [d3.csv(...)], data doesn't contain the data loaded from your CSV file, it contains only a d3 object, and you cannot plot that.

Instead, your call to d3.csv should look something like the following:

d3.csv("refugee_data.csv", function(d) {
  return {
        date: d.Year + "/" +d.Month,
        origin: d.Origin,
        asylum: d.Asylum,
        value: +d.Value
  };
}, function(error, rows) {
  console.log(rows);
  render(rows);
});

where render is a function that d3 will call to draw your graph when the data has finished loading.

I created a render function that contained the contents of your code from the line var w = 800; to the lines beginning var y = ..., followed by the contents of the plot function. I also replaced this.selectAll with svg.selectAll, and remove the use of plot.call. The render function I wrote ended up as follows:

function render(data) {
    var w = 800;
    var h = 450;
    var margin = {
        top: 58,
        bottom: 100,
        left: 80,
        right: 40
    };
    var width = w - margin.left - margin.right;
    var height = h - margin.top - margin.bottom;

    var svg = d3.select("body").append("svg")
                .attr("id", "chart")
                .attr("width", w)
                .attr("height", h);
    var dateParser = d3.time.format("%Y/%B").parse;
    var x = d3.time.scale()
             .domain(d3.extent(data, function(d){
                var date = dateParser(d.date);
                return date;
            }))
            .range([0,width]);

    var y = d3.scale.linear()
            .domain([0, d3.max(data, function(d){
                return d.value;
            })])
            .range([height,0]);   

        //enter()
        svg.selectAll(".point")
                .data(data)
                .enter()
                    .append("circle")
                    .classed("point", true)
                    .attr("r", 2);
        //Update
        svg.selectAll(".point")
        .attr("cx", function(d){
            var date = dateParser(d.date);
            return x(date);
        })
        .attr("cy", function(d){
            return y(d.value);
        })

        //Exit()
        svg.selectAll(".point")
        .data(data)
        .exit()
        .remove();
}

After making these changes I was able to see your graph working.

Upvotes: 2

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