I want to make a scale that is linear between 50 and 100, but if any outlier value is below 50 or above 100, gets coerced to a value of either 50 or 100, respectively, so that it doesn't fall off the visible range of my chart. (The plan is then to style those data points differently so that the user knows they're either more than or less than what they appear to be.)
How would I go about make a linear piecewise scale in D3 that does this? Or is it easier just to make a "gatekeeper" function that gets called directly by the SVG's y attribute, does those coercions manually, and then calls a regularly linear scale with "in-range" values, so that "out-of-range" values are never sent to the regular linear scale in the first place?
I think you are over complicating this.
I'm sure you are using a d3.line function, just cap the values in the y accessor:
var line = d3.line()
.x(function(d) { return x(d.x); })
.y(function(d) {
if (d.y > 150) return y(150);
else if (d.y < 50) return y(50);
else return y(d.y);
});
Actually, I just realized that linear.clamp(true) does exactly what I wanted.
Related
Let's say I have 16 circles in an 2 x 8 grid:
svg = d3.select(body).append('svg').attr('height,h).attr('width',w);
svg.selectAll('.centroids')
.data(d3.range(0,16))
.enter()
.append('circle')
.attr('class','centroids')
.attr('r','5')
.attr('cx', function(d,i) { return i * 10; })
.attr('cy', function(d,i) {
if (i > 7) return 20;
return 10;
});
Given a random coordinate in that space, how do I determine the nearest .centroid point?
One way in N time is of course to loop through all the points, measuring the hypotenuse to the difference in x and y coordinates, choosing the smallest value.
I'd like to find a better way though. Does anyone know an optimized way?
Optimization will depend on your exact settings:
if you have a few nodes (16 as in your example), in random positions, then your method is probably optimal (just compute the square of the hypotenuse, which gains a few square root operations).
if you have many nodes in random positions, you'll want to start considering quadtrees to manage your nodes. The overhead is not negligible, so don't bother about it until you have hundreds or thousands or nodes. On the plus side, d3has it all coded for you.
for a grid:
var startx=0;
var offsetx=10;
var cols=8;
var starty=10;
var offsety=10;
var rows=2;
var xi=d3.median([0,cols-1, Math.round((x-startx)/stepx)])
var yi=d3.median([0,rows-1, Math.round((y-starty)/stepy)])
var i=xi + yi*cols
this is constant time, adjust the (many) constants according to your dimensions.
A bit of details: (x-startx)/stepx allows to scale the coordinates so that the first dot is at 0, the next at 1, etc. Math.round gives the nearest integer, d3.median pushes the result between 0 and cols-1 (check out each case, by all mean it's nicer than nested ifs).... overall this gives the index of the nearest column, then you do the same for the rows, and there you are!
According to the d3 docs:
When interpolating to or from zero, some interpolated values may be very small. JavaScript formats small numbers in exponential notation, which unfortunately is not supported by CSS. For example, when transitioning opacity to fade in or out, the number 0.0000001 is converted to the string "1e-7" and then ignored, giving the default value of 1! To avoid distracting flicker, start or end the transition at 1e-6 rather than 0; this is the smallest value not formatted in exponential notation.
This is giving me a problem with a histogram which has some very low frequencies. The rectangle height is interpolated as a scientific number which throws an error. I've tried the following:
svg.selectAll(".bar")
.data(freq)
.filter(function(d) {return d.freq>0.005})
.transition()
.duration(1000)
.attr("y", function(d) { return y(d.freq); })
.attr("height", function(d) { return height - y(d.freq) })
This avoids the end value being zero - but how do I filter out those elements where the initial value may be close to zero?
You can do the same thing when you're creating the bars, i.e.
svg.selectAll("rect").data(freq).filter(...)
.enter().append("rect");
At this point, it would actually make sense to prefilter your data before passing it to D3 at all, i.e. use something like var filteredData = data.filter(...) and use filteredData.
I'm building my first line graph in d3:
http://jsfiddle.net/j94RZ/
I want to know how to utilize either the scale or axis allow me to draw a grid (of, presumably rectangles) where I can set a different background colour for each of the section of the grid...so I can alternate colours for each cell of the grid. I want the grid to be drawn and be constrained by the axes of my graph and then also adapt if the spacing of the axes ticks change (i.e. the axes changes like this: http://bl.ocks.org/mbostock/1667367). So if my graph has an x axis with 4 ticks and a y axis of 7 ticks then my graph will have a background grid that's 7 blocks high and 4 blocks wide.
I've been playing with the idea of using a range which starts at zero and ends at the full width of the graph but I don't know what value I can use for the step. Is there any way to sort of query the axis and return how many ticks there are?
var gridRange = d3.range(0, width, step?);
A better approach than your current solution would be to use scale.ticks() explicitly to get the tick values. The advantage of that is that it will still work if you change the number of ticks for some reason.
To get an alternating grid pattern instead of a single fill, you can use something like this code.
.attr("fill", function(d, i) {
return (i % 2) == 1 ? "green" : "blue";
})
Finally, to get the full grid pattern, you can either use an explicit loop as you've suggested, or nested selections. The idea here is to first pass in the y ticks, create a g element for each and then pass the x ticks to each one of these groups. In code, this looks something like this.
svg.selectAll("g.grid")
.data(y.ticks()).enter().append("g").attr("class", "grid")
.selectAll("rect")
.data(x.ticks()).enter().append("rect");
To set the position, you can access the indices within the top and bottom level data arrays like this.
.attr("x", function(d, i) {
return xScale(i);
})
.attr("y", function(d, i, j) {
return yScale(j);
})
To set the x position, you need the index of the inner array (passed to the set of g elements), which can be accessed through the second argument of your callback. For the outer array, simply add another argument (j here).
And that's really all there is to it. Complete jsfiddle here. To update this grid dynamically, you would simply pass in the new tick values (gotten from scale.ticks()), match with the existing data, and handle the enter/update/exit selections in the usual manner.
If you want to do without the auxiliary scales (i.e. without .rangeBand()), you can calculate the width/height of the rectangles by taking the extent of the range of a scale and dividing it by the number of ticks minus 1. Altogether, this makes the code a bit uglier (mostly because you need one fewer rectangle than ticks and therefore need to subtract/remove), but a bit more general. A jsfiddle that takes this approach is here.
So after a few helpful comments above I've got close to a solution. Using Ordinal rangebands get me close to where I want to go.
I've created the range bands by using the number of ticks on my axis as a basis for the range of the input domain:
var xScale = d3.scale.ordinal()
.domain(d3.range(10))
.rangeRoundBands([0, width],0);
var yScale = d3.scale.ordinal()
.domain(d3.range(4))
.rangeRoundBands([0, height],0);
I've then tried drawing the rectangles out like so:
svg.selectAll("rect")
.data(p)
.enter()
.append("rect")
.attr("x", function(d, i) {
return xScale(i);
})
.attr("y", function(d,i) {
0
})
.attr("width", xScale.rangeBand())
.attr("height", yScale.rangeBand())
.attr("fill", "green").
attr('stroke','red');
This gets me the desired effect but for only one row deep:
http://jsfiddle.net/Ny2FJ/2/
I want,somehow to draw the green blocks for the whole table (and also without having to hard code the amount of ticks in the ordinal scales domain). I tried to then apply the range bands to the y axis like so (knowing that this wouldn't really work though) http://jsfiddle.net/Ny2FJ/3/
svg.selectAll("rect")
.data(p)
.enter()
.append("rect")
.attr("x", function(d, i) {
return xScale(i);
})
.attr("y", function(d,i) {
return yScale(i);
})
.attr("width", xScale.rangeBand())
.attr("height", yScale.rangeBand())
.attr("fill", "green").
attr('stroke','red');
The only way I can think to do this is to introduce a for loop to run the block of code in this fiddle http://jsfiddle.net/Ny2FJ/2/ for each tick of the y axis.
I am drawing circles by setting a fixed x position but a changing y position. The problem is the circles are overlapping since the radius of each circle is different.
Ideally in theory to solve that I would probably want to get the y position of the previous circle and add the radius of the current circle to it to get the y position of the current circle. Correct me if I am thinking it wrong.
Right now I am doing something like this now
var k = 10;
var circleAttributes = circles.attr("cx", '150')
.attr("cy", function (d) {
return (k++) * 10; //this is a very gray area
})
And I am getting an overlap. Ideally I would like to space the circles form each other. Even if the outer edges touch each other I could live with that. How should I approach it?
I am writing a range which i am using to get the radius
var rScale = d3.scale.linear()
.domain([min, max])
.range([10, 150]);
and simply passing that as the radius like this
.attr("r", function(d) { return rScale(d.consumption_gj_);})
This is my fiddle
http://jsfiddle.net/sghoush1/Vn7mf/27/
Did a solution here: http://tributary.io/inlet/6283630
The key was to keep track of the sum of the radius of all previous circles. I did that in a forEach loop:
data.forEach(function(d,i){
d.radius = rScale(d.consumption_gj_);
if (i !== 0){
d.ypos = d.radius*2 + data[i-1].ypos;
}
else {
d.ypos = d.radius*2;
}
})
then, when setting the attributes of the circles you can use your new d.radius and d.ypos
var circleAttributes = circles.attr("cx", '150')
.attr("cy", function (d,i) {
return d.ypos + 5*i;
})
.attr("r", function(d) { return d.radius;})
The Charge Property
The charge in a force layout refers to how nodes in the environment push away from one another or attract one another. Kind of like magnets, nodes have a charge that can be positive (attraction force) or negative (repelling force).
From the Documentation:
If charge is specified, sets the charge strength to the specified value. If charge is not specified, returns the current charge strength, which defaults to -30. If charge is a constant, then all nodes have the same charge. Otherwise, if charge is a function, then the function is evaluated for each node (in order), being passed the node and its index, with the this context as the force layout; the function's return value is then used to set each node's charge. The function is evaluated whenever the layout starts.
A negative value results in node repulsion, while a positive value results in node attraction. For graph layout, negative values should be used; for n-body simulation, positive values can be used. All nodes are assumed to be infinitesimal points with equal charge and mass. Charge forces are implemented efficiently via the Barnes–Hut algorithm, computing a quadtree for each tick. Setting the charge force to zero disables computation of the quadtree, which can noticeably improve performance if you do not need n-body forces.
A good tutorial that will help you see this in action:
http://vallandingham.me/bubble_charts_in_d3.html
I have a zoomable area plot done in D3, which works well. Now I am trying to add a rectangle to the specified location along x-axis in the middle of the plot. However, I can't seem to figure out how to do that. "rect" element is specified using absolute (x,y) of the plot and so when using zooms it stays in the same position.
So I was wondering if there is a way to tie "rect" to the axis when plotting, so that it benefits from all the zoom and translate behaviour or do I need to manually edit the x,y,width and length of the rectangle according to translation as well as figuring out where the corresponding x and y coordinates are on the graph? I am trying to use "rect" because it seems the most flexible element to use.
Thanks
Alex
I'm not sure how you are doing the zooming, but I am guessing you are changing the parameters of the scales you use with your axis? You should be able to use the same scales to place your rectangle.
If you are starting with plot coordinates then maybe using the invert function on the scale will help (available at least for quantitive scales), e.g. https://github.com/mbostock/d3/wiki/Quantitative-Scales#wiki-linear_invert
You should be able to take initial plot coordinates and invert them to determine data coordinates that can then move with changes in the scale.
If the scale is linear you can probably invert the length and width too, but you will have to compute offsets if your domain does not include 0. Easiest is to compute the rectangle's end points, something like:
var dataX0 = xScale.invert(rect.x);
var dataX1 = xScale.invert(rect.x + rect.width);
var dataWidth = dataX1 - dataX0;
If you have the data in axes coordinates already you should be able to do something like:
var rectData = [{x: 'April 1, 1999', y: 10000, width: 100, height:100}];
svg.selectAll('rect.boxy')
.data(rectData)
.enter().append('rect').classed('boxy', true)
.style('fill','black');
svg.selectAll('rect.boxy')
.attr('x', function(d) { return x(new Date(d.x));} )
.attr('y', function(d) { return y(d.y);})
.attr('width', function(d) { return d.width;} )
.attr('height', function(d) { return d.height;} );
Based on the example you shared where x and y (as functions) are the scales the axes are based on.