This example shows one way to visualize the attendence record of a meetup The collected data is here and has been processed to the required data format.
Link to sequence explorer on github.
Modified http://d3js.org/d3.v4.js to a secure url
Modified http://www.ankerst.de/lib/sankeySeqExplorer_10.min.js to a secure url
Modified http://www.ankerst.de/lib/sankeySeq_10.min.js to a secure url
https://d3js.org/d3.v4.js
https://www.ankerst.de/lib/sankeySeqExplorer_10.min.js
https://www.ankerst.de/lib/sankeySeq_10.min.js