Proper way to draw gridlines - d3.js

Question

Okay, I'm starting to get a little more familiar with D3 but am still a little hazy on some things. I'm now trying to draw grid lines but am realizing that I may be hacking away versus doing it correctly. I tried to add some gridlines, using a tutorial, but ended up with a lot of code that I seem to be jimmy rigging in order to get it to line up properly. I was wondering if anyone could point me to a better way of writing this...
The original code is this.
<script type="text/javascript">
//Width and height
var w = 800;
var h = 400;
var padding = 20;
var border=1;
var bordercolor='black';
var dataset = [
[5, 20], [480, 90], [250, 50], [100, 33], [330, 95],[-50,-100],[50,-45],
[410, 12], [475, 44], [25, 67], [85, 21], [220, 88],[-480, -467], [3,-90],[468,481]
];
// create scale functions
var xScale = d3.scale.linear()
.domain([d3.min(dataset, function(d) { return d[0]; }), d3.max(dataset, function(d) { return d[0]; })])
.range([padding, w - padding * 2]);
var yScale = d3.scale.linear()
.domain([d3.min(dataset, function(d) { return d[0]; }), d3.max(dataset, function(d) { return d[1]; })])
.range([h - padding, padding]);
var rScale = d3.scale.linear()
.domain( [-100, d3.max(dataset, function(d) { return d[1]; })] )
.range([2,5]);
//Create SVG element
var svg = d3.select("body")
.append("svg")
.attr("width", w)
.attr("height", h)
.attr("border",border)
;
//define X axis this is rly a function, remember, variables can hold functions in JS
var xAxis = d3.svg.axis()
.scale(xScale)
.orient("bottom")
.ticks(1)
.tickSize(-h, 0, 0)
; //Set rough # of ticks
//Define Y axis
var yAxis = d3.svg.axis()
.scale(yScale)
.orient("left")
.ticks(1)
.tickSize(-w, 0, 0)
;
//create the circles
svg.selectAll("circle")
.data(dataset)
.enter()
.append("circle")
.attr("cx", function(d) {
return xScale(d[0]);
})
.attr("cy", function(d) {
return yScale(d[1]);
})
.attr("r", 3);
// draw axes here
svg.append("g")
.attr("class", "axis") //assign "axis" class
.attr("transform", "translate(0," + (h - padding) +")")
.call(xAxis);
svg.append("g")
.attr("class", "axis") //assign "axis" class
.attr("transform", "translate(" + padding + ",0)" )
.call(yAxis);
// end draw axes here
</script>
and the code I added in the second link is here
var vis = svg.append("svg:g")
.attr("transform", "translate(20,0)")
var rules = vis.append("svg:g").classed("rules", true)
rules.append("svg:g").classed("grid x_grid", true)
.attr("transform", "translate(-20,"+h+")")
.call(d3.svg.axis()
.scale(xScale)
.orient("bottom")
.ticks(4)
.tickSize(-h,0,0)
.tickFormat("")
)
rules.append("svg:g").classed("grid y_grid", true)
.call(d3.svg.axis()
.scale(yScale)
.orient("left")
.ticks(5)
.tickSize(-w,0,0)
.tickFormat("")
)
rules.append("svg:g").classed("labels x_labels", true)
.attr("transform", "translate(-20,"+ h +")")
.call(d3.svg.axis()
.scale(xScale)
.orient("bottom")
.ticks(4)
.tickSize(0)
.tickFormat("")
// .tickFormat(d3.time.format("%Y/%m"))
)
rules.append("svg:g").classed("labels y_labels", true)
.call(d3.svg.axis()
.scale(yScale)
.orient("left")
.ticks(5)
.tickSubdivide(1)
.tickSize(0, 0, 0)
.tickFormat("")
)
Again, really appreciate any help

Answer 1

Assuming that you have Mike Bostock's standard margins defined and you have defined a linear scale for the y-axis the following code will create horizontal gridlines without using tickSize().
svg.selectAll("line.horizontalGrid").data(yScale.ticks(4)).enter()
.append("line")
.attr(
{
"class":"horizontalGrid",
"x1" : margin.right,
"x2" : width,
"y1" : function(d){ return yScale(d);},
"y2" : function(d){ return yScale(d);},
"fill" : "none",
"shape-rendering" : "crispEdges",
"stroke" : "black",
"stroke-width" : "1px"
});

Answer 2

I would suggest to use d3.svg.axis().scale() to tie up the grid to your coordinates. I drew a quick example based on your code: http://jsfiddle.net/temirov/Rt65L/1/
The gist is to use the existing scales, x and y, and to use ticks as grid. Since yAxis and xAxis are already defined we can just re-use them. Here is the relevant code:
//Draw a grid
var numberOfTicks = 6;
var yAxisGrid = yAxis.ticks(numberOfTicks)
.tickSize(w, 0)
.tickFormat("")
.orient("right");
var xAxisGrid = xAxis.ticks(numberOfTicks)
.tickSize(-h, 0)
.tickFormat("")
.orient("top");
svg.append("g")
.classed('y', true)
.classed('grid', true)
.call(yAxisGrid);
svg.append("g")
.classed('x', true)
.classed('grid', true)
.call(xAxisGrid);

Answer 3

You could use the ticks() function of your scale to get the tick values and then use them in a data call to draw the lines.
var ticks = xScale.ticks(4);
rules.selectAll("path.xgrid").data(ticks).enter()
.append("path")
.attr("d", function(d) {
return "M" + xScale(d) + " " + padding + "L" + xScale(d) + " " + (h-padding);
});
You may prefer using a line generator for the grid lines instead of creating the path manually. This works similarly for y grid lines, only that the y coordinate is constant and ranges from 0 to width of graph. You may need to adjust the start and end values to make it look "nice".

Answer 4

In the d3fc project we have created a gridlines component that renders in exactly the same way as the D3(v4) axis.
Here's an example of the usage:
var width = 500, height = 250;
var container = d3.select("#gridlines")
.append("svg")
.attr("width", width)
.attr("height", height);
var xScale = d3.scaleLinear()
.range([0, 100]);
var yScale = d3.scaleLinear()
.range([0, 100]);
var gridline = fc.annotationSvgGridline()
.xScale(xScale)
.yScale(yScale);
container.append("g")
.call(gridline);
Which renders as follows:
The spacing of the gridlines is determined by the ticks supplied by the associated axes.
Disclosure: I am a core contributor to the d3fc project!

Answer 5

Following #arete's idea, you can use the following to avoid re-drawing unnecessarily the gridline:
function createsGrid(data) {
var grid = gridLine.selectAll("line.horizontalGrid").data(scaleY.ticks());
grid.enter()
.append("line")
.attr("class","horizontalGrid");
grid.exit().remove();
grid.attr({
"x1":0,
"x2": width,
"y1": function (d) { return scaleY(d); },
"y2": function (d) { return scaleY(d); }
});
}
and define the following in your CSS file
line.horizonalGrid{
fill : none;
shape-rendering : crispEdges;
stroke : black;
stroke-width : 1.5px;
}

Answer 6

You could just use innerTickSize, instead of tickSize:
var xAxis = d3.svg.axis()
.scale(xScale)
.orient("bottom")
.ticks(1)
.innerTickSize(-h);

Answer 7

Use tickSizeInner()
// x axis
var x = d3.scaleLinear().range([0, width]).domain([0, 100000]);
svg
.append("g")
.call(d3.axisBottom(x).ticks(10).tickSizeInner(-height))