Database Reference
In-Depth Information
With the maximum value set to 1 , the background element can be drawn a
single time, and then the foreground element can be redrawn each time a
new value is made available:
back.attr("d",arc(1));
$(document).on('data:'+name,function(event,data) {
front.attr("d",arc(data));
});
In addition to being easier to implement, the paths produced by the arc
generator (and other generators where appropriate) are regions rather than
lines. This means that they can have separate fill and stroke styling whereas
the previous examples used the stroke width to simplify the rendering.
Joining Selections and Data
When the data is simple, using D3 directly is an easy way to develop
quick-and-dirtyvisualizations.Whenthingsgetmorecomplicated,D3really
comes into its own as the power of its join operations can be combined with
its selection operators.
To join an array of data to a selection, the data method of the selection is
used. The resulting join is comprised of three subselections:
The update selection: This is the set that contains elements in the
document that already correspond to elements of the data array.
The enter selection: This is the set of data array elements that do not
(yet) correspond to document elements.
The exit selection: This is the set of document elements that have no
corresponding element in the data array.
The update selection is the default selection returned by the data method.
The other two selections are accessed with the enter() and exit()
methods, respectively.
The usual order is to first work with the enter selection. This selection
is special in two ways. First, it only affects the document manipulation
methods such as append . Secondly, when the append() or insert()
methods are used, the resulting elements are immediately added to the
update selection. This reduces code duplication by allowing all of the
attributes and styles to be modified on the update selection. If, for some
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