Multivariate Charts from HTML tables in D3.js

For a dynamic monovariate (single line) chart, please see my earlier post –

Sometimes you just have to plot more than one dataset on the same chart, but you might have a complex data table with some “collections” of single-values and some collections of multiple values. Here I’ve put together an example from something I’ve been working on recently. Once your back-end queries (SQL or whatever) are written and your templates convert those data into basic HTML tables, you can plot then straight to SVG/D3 without much extra work.

Nearly all of that extra work is around adding appropriate classes to cells to distinguish columns and collections of columns. The rest is to extract those cells out again and decide which should be plotted together.

In this example, tabs and table headings belong to classes “collection_#” “a_c#” where the collection_# identifies a set of columns to be displayed together and the a_c# identifies the (links for the) columns themselves. Collections with multiple columns therefore have a single collection class but contain more than one a_c# class.

Next each table tbody td data cell belongs to a c# class, one for each column. Each one is also uniquely identified by a td#_<date> which allows hovers on the table cell to highlight the SVG data point and vice versa. Next each cell contains a span with a “val” class (more on that in the next post).

SVG paths may now be built for each column. Clicks on table-headings and tabs are able to examine which columns co-display because they belong in the same collection and then scale and plot them appropriately.

Note that the first and last tabs in this example plot single lines to demonstrate mixed collections in action. The middle two tabs have two lines each but there’s no reason why you couldn’t have more (although there are only seven colours listed at the moment).