understanding dc interaction with crossfilter objects

1
votes

Though I can write dc.js applications, I still don't understand how dc uses crossfilter objects, ie the dimensions and groups in various charts. When we click on an graph element, for instance, a pie chart slice, I believe dc is applying filters on the dimension, but does it manipulate the crossfilter object as well? Anyone knows of any document/article explaining how dc interacts with crossfilter objects? I know of http://www.codeproject.com/Articles/693841/Making-Dashboards-with-Dc-js-Part-Using-Crossfil which is really good for beginners, but it does not go deep dive on this specific subject.

For instance, I have this dc chart: http://bit.ly/1nStSh3

Basically the dataset has object names (4 of them, P, Q, S, T) and its size for various dates. The two piecharts show the size for dates and objects respectively. There is a line chart which shows the data growth over a period of time. Now, when I click on the second graph, ie object names, both line chart and the first pie chart auto adjusts, but when I click on the first pie chart, the line chart does not change.

1
dc.jscrossfilter

1 Answers

3
votes

Your particular question is covered by the crossfilter documentation and the dc.js FAQ: a dimension does not observe its own filters, but only the filters on other dimensions.

To get the charts to respond to each other, create a duplicate of the dimension (construct another one with the same arguments) and put the charts on separate dimensions. (There is also work underway to reflect the brushing/filter state between charts that share the same dimension.)

As to your larger question, no, there is no documentation on the interaction between dc.js and crossfilter that I know of. As the principle maintainer (but not the original author) of dc.js, I hope to write such documentation in the next year.

There actually isn't much magic to it: charts just update the dimension filters and then trigger redraws on the charts in their group. The d3 transitions within each chart are what make it look fancier than that.