Develop Reference

x-axis zooming with d3 line charts - javascript

I'm just getting into using d3, and relatively novice in js still. I'm trying to set up a page of log file visualizations for monitoring some servers. Right now I'm focusing on getting a line chart of CPU utilization, where I can focus on specific time periods (So an x-zoom only). I am able to do a static charts easily, but when it comes to the zooming the examples are going over my head and I can't seem to make them work.
This is the static example I followed to get things up and running, and this is the zoom example I've been trying to follow.
My input csv is from a rolling set of log files (which will not be labled on the first row), each row looks like this:
datetime,server,cpu,memory,disk,network_in,network_out
So far what I've been able to get on the zoom looks like this:
var parseDate = d3.time.format("%Y-%m-%d %H:%M:%S").parse;
// define dimensions of graph
var margin = {top: 20, right: 80, bottom: 30, left: 50},
width = 960 - margin.left - margin.right,
height = 200 - margin.top - margin.bottom;
var x = d3.time.scale().range([0, width]);
var y = d3.scale.linear().range([height, 0]);
var xAxis = d3.svg.axis()
.scale(x)
.orient("bottom")
.tickSize(-height, 0)
.tickPadding(6);
var yAxis = d3.svg.axis()
.scale(y)
.orient("left")
.tickSize(-width)
.tickPadding(6);
// Define how we will access the information needed from each row
var line = d3.svg.line()
.interpolate("step-after")
.x(function(d) { return x(d[0]); })
.y(function(d) { return y(d[2]); });
// Insert an svg element into the document for each chart
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 + ")");
// Declare zoom handler
var zoom = d3.behavior.zoom().on("zoom", draw);
// Open the log and extract the information
d3.text("log.csv", function(text) {
var data = d3.csv.parseRows(text).map(function(row) {
return row.map(function(value, index) {
if (index == 0) {
return parseDate(value);
}
else if (index > 1) {
return +value;
}
else {
return value;
}
});
});
// Set the global minimum and maximums
x.domain(d3.extent(data, function(d) { return d[0]; }));
y.domain(d3.extent(data, function(d) { return d[2]; }));
zoom.x(x);
// Finally, we have the data parsed, and the parameters of the charts set, so now we
// fill in the charts with the lines and the labels
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")
.attr("text-anchor", "end")
.text("Percent (%)");
svg.append("path")
.datum(data)
.attr("class", "line")
.attr("d", line);
svg.append("text")
.attr("x", margin.left)
.attr("y", 0 - (margin.top / 2))
.attr("text-anchor", "middle")
.text('all');
svg.append("rect")
.attr("class", "pane")
.attr("width", width)
.attr("height", height)
.call(zoom);
svg.select("path.line").data([data]);
draw();
});
function draw() {
svg.select("g.x.axis").call(xAxis);
svg.select("g.y.axis").call(yAxis);
svg.select("path.line").attr("d", line);
}
What this gives me is a very sluggish chart that can be zoomed and panned, but it does not clip off the line at the ends of the chart. I've tried adding in the clipping elements described in the example, but that ends up fully erasing my line every time.
Thanks for any help or direction

Related

This question already has answers here:
Why does click event handler fire immediately upon page load?
(4 answers)
Closed 4 years ago.
I'm getting introduced to javascript and I'm trying to use .on("mouseovert", ...) in order to get the x-value of my graph when the cursor is upon the graph.
My code look like this:
// do something as mouseover the graph
svg.select("svg")
.on("mouseover", alert("mouse on graph"));
The result is: an alert appears when I open the html file (and loading my js script), but nothing happen as is hover the graph.
Everything else in the script works fine.
Do you know why?
Thank you very much for the time you take!
Here is the full script:
function draw_co2(url) {
d3.select("svg").remove() //remove the old graph
// set the dimensions and margins of the graph
var margin = {
top: 20,
right: 20,
bottom: 30,
left: 50
},
width = 960 - margin.left - margin.right,
height = 500 - margin.top - margin.bottom;
// parse the date / time
var parseTime = d3.timeParse("%Y-%m-%d");
// Get the data
d3.json(url, function (error, data) {
if (error)
throw ('There was an error while getting geoData: ' + error);
data.forEach(function (d) {
d.Date = parseTime(d.Date);
d.Trend = +d.Trend;
});
// set the ranges // Scale the range of the data
var x = d3.scaleTime().domain([new Date("1960"), new Date("2015")]).range([0, width]);
var y = d3.scaleLinear()
.domain([d3.min(data, function (d) {
return d.Trend;
}) - 1 / 100 * d3.min(data, function (d) {
return d.Trend;
}), d3.max(data, function (d) {
return d.Trend;
}) + 1 / 100 * d3.min(data, function (d) {
return d.Trend;
})])
.range([height, 0]);
// define the line
var valueline = d3.line()
.x(function (d) {
return x(d.Date);
})
.y(function (d) {
return y(d.Trend);
});
// append the svg obgect to the body of the page
// appends a 'group' element to 'svg'
// moves the 'group' element to the top left margin
var svg = d3.select("#graph_draw").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 + ")");
//Y Axis label
svg.append("g")
.call(d3.axisLeft(y))
.append("text")
.attr("fill", "#000")
.attr("transform", "rotate(-90)")
.attr("y", 6)
.attr("dy", "0.71em")
.attr("text-anchor", "end")
.text("Carbon dioxide (ppm)");
// Add the valueline path.
svg.append("path")
.data([data])
.style("opacity", 0)
.transition()
.duration(1000)
.style("opacity", 1)
.attr("class", "line")
.attr("d", valueline);
// Add the X Axis
svg.append("g")
.attr("transform", "translate(0," + height + ")")
.call(d3.axisBottom(x));
// Add the Y Axis
svg.append("g")
.call(d3.axisLeft(y));
// gridlines in x axis function
function make_x_gridlines() {
return d3.axisBottom(x)
.ticks(10);
};
// add the X gridlines
svg.append("g")
.attr("class", "grid")
.attr("transform", "translate(0," + height + ")")
.call(make_x_gridlines()
.tickSize(-height)
.tickFormat(""));
// do something as mouseover the graph
svg.select("svg")
.on("mouseover", alert("mouse on graph"));
})
}

Use mouser over as an inline function
svg.select("svg")
.on("mouseover", function () {
alert("mouse on graph")
});

Looking at this Histogram chart using d3 example I plugged in my data but it had some strange side effects e.g. after refreshing to a new dataset, some information from the previous dataset i.e. x-axis scale was retained. I tried deleting and appending a new x-axis etc but nothing worked.
This happened due to the fact that my datasets had completely different x-axis ranges and scales. The only way I found to make it work was to select the whole svg element, remove it and re-append everything anew. However, this doesn't make a pleasant transition for the user so I was wondering how can this be improved to make it refreshable using transitions as in the original example even when having datasets with different x-scales and ranges.
This was my last approach which is a bit harsh to the eye:
// delete old
d3.select("#" + divId).select("svg").remove();
// then recreate all new
And this was my refresh attempt (integrated with AngularJS). Note how it has some common initialization and then if the SVG doesn't exist appends everything new otherwise tries to update it. I went bit by bit but can't see why the refresh doesn't remove all the previous dataset information of the x-axis scale:
var divId = $scope.histogramData.divId;
var color = $scope.histogramData.color;
var values = $scope.histogramData.data[$scope.histogramData.selected];
var svg = $scope.histogramData.svg;
// plot common initialization
var margin = {top: 40, right: 20, bottom: 20, left: 20},
width = 450 - margin.left - margin.right,
height = 370 - margin.top - margin.bottom;
var max = d3.max(values);
var min = d3.min(values);
var x = d3.scale.linear()
.domain([min, max])
.range([0, width]);
// generate a histogram using twenty uniformly-spaced bins.
var data = d3.layout.histogram()
.bins(x.ticks(10))
(values);
var yMax = d3.max(data, function(d){ return d.length });
var yMin = d3.min(data, function(d){ return d.length });
var colorScale = d3.scale.linear()
.domain([yMin, yMax])
.range([d3.rgb(color).brighter(), d3.rgb(color).darker()]);
var y = d3.scale.linear()
.domain([0, yMax])
.range([height, 0]);
var xAxis = d3.svg.axis()
.scale(x)
.orient("bottom");
// ===================================================================
// If the SVG doesn't exist then adds everything new
// ===================================================================
if (svg === undefined) {
var svg = d3.select("#" + divId)
.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 + ")");
$scope.histogramData.svg = svg;
var bar = svg.selectAll(".bar")
.data(data)
.enter()
.append("g")
.attr("class", "bar")
.attr("transform", function(d) { return "translate(" + x(d.x) + "," + y(d.y) + ")"; });
bar.append("rect")
.attr("x", 1)
.attr("width", (x(data[0].dx) - x(0)) - 1)
.attr("height", function(d) { return height - y(d.y); })
.attr("fill", function(d) { return colorScale(d.y) });
bar.append("text")
.attr("dy", ".75em")
.attr("y", -12)
.attr("x", (x(data[0].dx) - x(0)) / 2)
.attr("text-anchor", "middle")
.text(function(d) { return formatCount(d.y); });
var gTitle = svg.append("text")
.attr("x", 0)
.attr("y", 0 - (margin.top / 2))
.attr("text-anchor", "left")
.classed("label", true)
.text($scope.histogramData.spec[selected]);
$scope.histogramData.gTitle = gTitle;
var gAxis = svg.append("g")
.attr("class", "x axis")
.attr("transform", "translate(0," + height + ")")
.call(xAxis);
$scope.histogramData.gAxis = gAxis;
} else {
// ===================================================================
// If the SVG does exist then tries refreshing
// ===================================================================
var bar = svg.selectAll(".bar").data(data);
// remove object with data
bar.exit().remove();
bar.transition()
.duration(1000)
.attr("transform", function(d) { return "translate(" + x(d.x) + "," + y(d.y) + ")"; });
bar.select("rect")
.transition()
.duration(1000)
.attr("height", function(d) { return height - y(d.y); })
.attr("fill", function(d) { return colorScale(d.y) });
bar.select("text")
.transition()
.duration(1000)
.text(function(d) { return formatCount(d.y); });
var gTitle = $scope.histogramData.gTitle;
gTitle.transition()
.duration(1000)
.text($scope.histogramData.spec[selected]);
var gAxis = $scope.histogramData.gAxis;
gAxis.transition()
.duration(1000)
.call(xAxis);
}

I would suggest to keep this d3 code inside one angularJS directive and keep a watch on the json which you are using to plot that graph. As soon as values are changing the directive will be called again and the graph will be plotted. Hope it helps.

I am trying to populate a data set into D3's Bar chart data. I am using this example from the d3: http://bl.ocks.org/mbostock/3885304
Here is my sample data:
var data = [{"name":"0","members_count":4},{"name":"1","members_count":1},{"name":"2","members_count":6},{"name":"3","members_count":1},{"name":"4","members_count":1},{"name":"5","members_count":2},{"name":"6","members_count":4},{"name":"7","members_count":3},{"name":"8","members_count":5},{"name":"9","members_count":1},{"name":"10","members_count":2},{"name":"11","members_count":3},{"name":"12","members_count":2},{"name":"13","members_count":0},{"name":"14","members_count":5},{"name":"15","members_count":2},{"name":"16","members_count":2},{"name":"17","members_count":4},{"name":"18","members_count":2},{"name":"19","members_count":4},{"name":"20","members_count":3},{"name":"21","members_count":5},{"name":"22","members_count":8},{"name":"23","members_count":3},{"name":"24","members_count":2},{"name":"25","members_count":3},{"name":"26","members_count":4},{"name":"27","members_count":4},{"name":"28","members_count":1},{"name":"29","members_count":1},{"name":"30","members_count":3},{"name":"31","members_count":5},{"name":"32","members_count":4},{"name":"33","members_count":3},{"name":"34","members_count":6},{"name":"35","members_count":2},{"name":"36","members_count":2},{"name":"37","members_count":7},{"name":"38","members_count":2},{"name":"39","members_count":4},{"name":"40","members_count":2},{"name":"41","members_count":1},{"name":"42","members_count":8},{"name":"43","members_count":10},{"name":"44","members_count":1},{"name":"45","members_count":5},{"name":"46","members_count":2},{"name":"47","members_count":5},{"name":"48","members_count":3},{"name":"49","members_count":1},{"name":"50","members_count":9},{"name":"51","members_count":3},{"name":"52","members_count":2},{"name":"53","members_count":8},{"name":"54","members_count":2},{"name":"55","members_count":3},{"name":"56","members_count":2},{"name":"57","members_count":2},{"name":"58","members_count":5},{"name":"59","members_count":1},{"name":"60","members_count":2},{"name":"61","members_count":4},{"name":"62","members_count":2},{"name":"63","members_count":2},{"name":"64","members_count":6},{"name":"65","members_count":6},{"name":"66","members_count":1},{"name":"67","members_count":1},{"name":"68","members_count":3},{"name":"69","members_count":5},{"name":"70","members_count":3},{"name":"71","members_count":4},{"name":"72","members_count":4},{"name":"73","members_count":1},{"name":"74","members_count":3},{"name":"75","members_count":2},{"name":"76","members_count":4},{"name":"77","members_count":5},{"name":"78","members_count":2},{"name":"79","members_count":1},{"name":"80","members_count":2},{"name":"81","members_count":1},{"name":"82","members_count":4},{"name":"83","members_count":3},{"name":"84","members_count":1},{"name":"85","members_count":4},{"name":"86","members_count":1},{"name":"87","members_count":3},{"name":"88","members_count":1},{"name":"89","members_count":8},{"name":"90","members_count":6},{"name":"91","members_count":6},{"name":"92","members_count":3},{"name":"93","members_count":4},{"name":"94","members_count":5},{"name":"95","members_count":2},{"name":"96","members_count":3},{"name":"97","members_count":2},{"name":"98","members_count":3},{"name":"99","members_count":6},{"name":"100","members_count":3},{"name":"101","members_count":1},{"name":"102","members_count":0},{"name":"103","members_count":5},{"name":"104","members_count":2},{"name":"105","members_count":1},{"name":"106","members_count":7},{"name":"107","members_count":1},{"name":"108","members_count":1},{"name":"109","members_count":7},{"name":"110","members_count":5},{"name":"111","members_count":5},{"name":"112","members_count":2},{"name":"113","members_count":6},{"name":"114","members_count":1},{"name":"115","members_count":2},{"name":"116","members_count":1},{"name":"117","members_count":1},{"name":"118","members_count":10},{"name":"119","members_count":2},{"name":"120","members_count":6},{"name":"121","members_count":1},{"name":"122","members_count":1},{"name":"123","members_count":2},{"name":"124","members_count":4},{"name":"125","members_count":5},{"name":"126","members_count":1},{"name":"127","members_count":1},{"name":"128","members_count":1},{"name":"129","members_count":3},{"name":"130","members_count":3},{"name":"131","members_count":3},{"name":"132","members_count":4},{"name":"133","members_count":3},{"name":"134","members_count":1},{"name":"135","members_count":5},{"name":"136","members_count":5},{"name":"137","members_count":1},{"name":"138","members_count":2},{"name":"139","members_count":5},{"name":"140","members_count":1},{"name":"141","members_count":1},{"name":"142","members_count":2},{"name":"143","members_count":2},{"name":"144","members_count":4},{"name":"145","members_count":4},{"name":"146","members_count":3},{"name":"147","members_count":5},{"name":"148","members_count":2},{"name":"149","members_count":1},{"name":"150","members_count":2},{"name":"151","members_count":3},{"name":"152","members_count":0},{"name":"153","members_count":3},{"name":"154","members_count":1},{"name":"155","members_count":2},{"name":"156","members_count":2},{"name":"157","members_count":1},{"name":"158","members_count":5},{"name":"159","members_count":4},{"name":"160","members_count":4},{"name":"161","members_count":5},{"name":"162","members_count":4},{"name":"163","members_count":2},{"name":"164","members_count":4},{"name":"165","members_count":2},{"name":"166","members_count":2},{"name":"167","members_count":1},{"name":"168","members_count":1},{"name":"169","members_count":10},{"name":"170","members_count":4},{"name":"171","members_count":2},{"name":"172","members_count":2},{"name":"173","members_count":1},{"name":"174","members_count":5},{"name":"175","members_count":1},{"name":"176","members_count":1},{"name":"177","members_count":5},{"name":"178","members_count":3},{"name":"179","members_count":1},{"name":"180","members_count":5},{"name":"181","members_count":8},{"name":"182","members_count":4},{"name":"183","members_count":2},{"name":"184","members_count":1},{"name":"185","members_count":3},{"name":"186","members_count":1},{"name":"187","members_count":3},{"name":"188","members_count":1},{"name":"189","members_count":1},{"name":"190","members_count":6},{"name":"191","members_count":4},{"name":"192","members_count":5},{"name":"193","members_count":1},{"name":"194","members_count":4},{"name":"195","members_count":2},{"name":"196","members_count":2},{"name":"197","members_count":2},{"name":"198","members_count":0},{"name":"199","members_count":3},{"name":"200","members_count":3},{"name":"201","members_count":1},{"name":"202","members_count":1},{"name":"203","members_count":1},{"name":"204","members_count":5},{"name":"205","members_count":1},{"name":"206","members_count":1},{"name":"207","members_count":1},{"name":"208","members_count":1},{"name":"209","members_count":1},{"name":"210","members_count":5},{"name":"211","members_count":2},{"name":"212","members_count":1},{"name":"213","members_count":5},{"name":"214","members_count":1},{"name":"215","members_count":3},{"name":"216","members_count":1},{"name":"217","members_count":1},{"name":"218","members_count":4},{"name":"219","members_count":2},{"name":"220","members_count":1},{"name":"221","members_count":3},{"name":"222","members_count":1},{"name":"223","members_count":3},{"name":"224","members_count":1},{"name":"225","members_count":2},{"name":"226","members_count":1},{"name":"227","members_count":1},{"name":"228","members_count":11},{"name":"229","members_count":9},{"name":"230","members_count":9},{"name":"231","members_count":9},{"name":"232","members_count":10},{"name":"233","members_count":10},{"name":"234","members_count":10},{"name":"235","members_count":9},{"name":"236","members_count":10},{"name":"237","members_count":10},{"name":"238","members_count":10},{"name":"239","members_count":10},{"name":"240","members_count":9},{"name":"241","members_count":9},{"name":"242","members_count":9},{"name":"243","members_count":10},{"name":"244","members_count":10},{"name":"245","members_count":9},{"name":"246","members_count":2},{"name":"247","members_count":1},{"name":"248","members_count":2},{"name":"249","members_count":2},{"name":"250","members_count":1},{"name":"251","members_count":2},{"name":"252","members_count":1},{"name":"253","members_count":5},{"name":"254","members_count":1},{"name":"255","members_count":1},{"name":"256","members_count":1},{"name":"257","members_count":1},{"name":"258","members_count":1},{"name":"259","members_count":1},{"name":"260","members_count":2},{"name":"261","members_count":1},{"name":"262","members_count":1},{"name":"263","members_count":2},{"name":"264","members_count":1},{"name":"265","members_count":1},{"name":"266","members_count":1},{"name":"267","members_count":1},{"name":"268","members_count":2},{"name":"269","members_count":2},{"name":"270","members_count":1},{"name":"271","members_count":1},{"name":"272","members_count":0},{"name":"273","members_count":2},{"name":"274","members_count":1},{"name":"275","members_count":2},{"name":"276","members_count":2},{"name":"277","members_count":1},{"name":"278","members_count":3},{"name":"279","members_count":1},{"name":"280","members_count":1},{"name":"281","members_count":1},{"name":"282","members_count":1},{"name":"283","members_count":1},{"name":"284","members_count":1},{"name":"285","members_count":1},{"name":"286","members_count":1},{"name":"287","members_count":1},{"name":"288","members_count":1},{"name":"289","members_count":1},{"name":"290","members_count":1},{"name":"291","members_count":1},{"name":"292","members_count":1},{"name":"293","members_count":1},{"name":"294","members_count":1},{"name":"295","members_count":1},{"name":"296","members_count":1},{"name":"297","members_count":2},{"name":"298","members_count":2},{"name":"299","members_count":1},{"name":"300","members_count":1},{"name":"301","members_count":1},{"name":"302","members_count":1},{"name":"303","members_count":1},{"name":"304","members_count":1},{"name":"305","members_count":1},{"name":"306","members_count":1},{"name":"307","members_count":1},{"name":"308","members_count":1},{"name":"309","members_count":1},{"name":"310","members_count":1},{"name":"311","members_count":1},{"name":"312","members_count":1},{"name":"313","members_count":0},{"name":"314","members_count":1}]
This is chart's drawing code.
var margin = {top: 20, right: 20, bottom: 30, left: 40},
width = (960 - margin.left - margin.right) * data.length/50,
height = 500 - margin.top - margin.bottom;
var x = d3.scale.ordinal()
.domain([0,1])
.rangeRoundBands([0, width], 0.1);
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 + ")");
x.domain(data.map(function(d) { return d.name; }));
y.domain([0, d3.max(data, function(d) { return d.members_count; })]);
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("fill","green")
.attr("x", function(d) { return x(d.name); })
.attr("width", x.rangeBand())
.attr("y", function(d) { return y(d.members_count); })
.attr("height", function(d) { return height - y(d.members_count); });
This issue I am getting is that I have some white space which looks ugly. This space come before the 1st bar and also after the last bar of the chart. I have tried tweaking the x value of the bar, But I think that is not a good way to do.
This space does not come when the data set is small. But when dataset is large then this space comes up. How can I remove this space from the start and from end.

The problem is with this line in scale:
.rangeRoundBands([0, width], 0.1);
When there is not specified the third parameter outerPadding it adds before and after the chart extra space produced by the padding parameter for each bar. You have set the padding to 0.1. To solve this problem set the outerPadding parameter:
var x = d3.scale.ordinal()
.domain([0,1])
.rangeRoundBands([0, width], 0.1, 0);
Here is updated your code: http://jsfiddle.net/ojntup1a/

I am using D3 for the first time and I have followed the instructions on their site to get to this point. I cannot seem to get the chart to display although there are no exceptions in the JS console in Chrome.
Here's the JS in the header of my page:
<script>
var margin = {
top: 0,
right: 0,
bottom: 10,
left: 0
},
width = 838 - margin.left - margin.right,
height = 300 - 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");
var chart = d3.select(".day_chart")
.attr("width", width + margin.left + margin.right)
.attr("height", height + margin.top + margin.bottom)
.append("g")
.attr("transform", "translate(" + margin.left + "," + margin.top + ")");
d3.json("http://solarmonitoringaustralia.com.au/myphp/inverterdata.php?var=TEST1&id=C120031", function (error, data) {
data.forEach(function (d) {
d.hour = +d.hour; // coerce to number
d.max_energy = +d.max_energy;
alert(d.hour + " -- " + d.max_energy);
});
x.domain(data.map(function (d) {
return d.hour;
}));
y.domain([0, d3.max(data, function (d) {
return d.max_energy;
})]);
chart.append("g")
.attr("class", "x axis")
.attr("transform", "translate(0," + height + ")")
.call(xAxis);
chart.append("g")
.attr("class", "y axis")
.call(yAxis);
chart.selectAll(".bar")
.data(data)
.enter().append("rect")
.attr("class", "bar")
.attr("x", function (d) {
return x(d.hour);
})
.attr("y", function (d) {
return y(d.max_energy);
})
.attr("height", function (d) {
return height - y(d.max_energy);
})
.attr("width", x.rangeBand());
});
</script>
The code calls in a JSON request to a server side script. Here's the data it returns to the browser when executing the query:
[{"hour":"1","max_energy":"15.969"},{"hour":"2","max_energy":"19.065"},{"hour":"3","max_energy":"21.191"},{"hour":"4","max_energy":"23.151"},{"hour":"5","max_energy":"24.403"},{"hour":"6","max_energy":"25.082"},{"hour":"7","max_energy":"25.494"},{"hour":"8","max_energy":"25.499"},{"hour":"9","max_energy":"4.685"},{"hour":"10","max_energy":"7.309"},{"hour":"11","max_energy":"10.051"},{"hour":"12","max_energy":"13.119"}]
My HTML contains this tag where I want the chart to appear:
<sgv class="day_chart"></svg>
I can see the data passing into the JS above via the "alert" function in the data.forEach(function (d), so the data comes back.
The page loads but it loads with a blank area where the chart would go, and no JS errors in the console. Thanks for any advice!

Well, this one's going to be a face-palm moment.
The only thing wrong was a typo.
<sgv class="day_chart"></svg>
Should of course be
<svg class="day_chart"></svg>
I've got a working version here
http://jsfiddle.net/cZxey/11/
(I also set the library to load D3, and inserted hard-coded data. For working with the real data, just comment that out. Oh, and increase your bottom padding so your tick mark labels don't get cut off.)
--ABR

I'm working on a real-time visualization of incoming data. I use D3 for the visualization and started based on this example: http://bl.ocks.org/mbostock/3883195
This is the version I'm currently working on:
var margin = {top: 20, right: 20, bottom: 30, left: 50},
width = 500 - margin.left - margin.right,
height = 300 - margin.top - margin.bottom;
var x = d3.time.scale().range([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 area = d3.svg.area()
.x(function(d) { return x(d.x); })
.y0(height)
.y1(function(d) { return y(d.y); });
var svg = d3.select("div#chart").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 = [[1,1],[2,3],[3,2],[4,4]];
var dataCallback = function(d) {
d.x = +d[0];
d.y = +d[1];
};
data.forEach(dataCallback);
x.domain(d3.extent(data, function(d) { return d.x; }));
y.domain([0, d3.max(data, function(d) { return d.y; })]);
svg.append("path")
.datum(data)
.attr("class", "area")
.attr("d", area);
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("Number of Messages");
This produces the following graph:
Now, as it should update itself regularly, I wanted to dynamically update the data in the graph using the following code:
var n = svg.selectAll("path").data([5,20])
n.enter();
n.exit().remove();
However, that does not work. I'm new to D3 and still learning the basics. Ideally, the graph visualization shifts to the left and the new data is shown in the graph. But so far I can't even add new data to it. Could someone help me with that? I also searched for examples similar to this, but did not found anything which really helped me so far.

d3 is pretty good at keeping track of what data's been added and what's being removed - it does this with joins. Take a look at http://bl.ocks.org/mbostock/3808218
IF we use the data binding (instead of "datum")
svg.append("path")
.data([data])
.attr("class", "area")
.attr("d", area);
and then on update do something like:
// update the list of coordinates
data.splice(0,1);
data.push([5,20]);
// re-decorate the last, newly added item
dataCallback(data[data.length - 1]);
// You will also need to update your axes
x.domain(d3.extent(data, function(d) { return d.x; }));
y.domain([0, d3.max(data, function(d) { return d.y; })]);
// update the data association with the path and recompute the area
svg.selectAll("path").data([data])
.attr("d", area);
And you should get your area to update.
You can try it out here
With the way your data is organized using the joined data (instead of datum) may not make much difference. Note that here the (single) data element you are associating with the path is the full list of coordinates so to update the area you need to pass in a new full list of coordinates.
If you really want to minimized the amount you need to redraw you could break up the area and draw each line segment. Then essentially you fall back to the bar chart example but with not-flat bars and no spacing.