"Germany talks" -- this was the motto at ZEIT online in summer 2017, as part of the experimental new ressort D17. Our message was simple: When people like Donald Trump and Victor Orbán where polarizing people in their countries, we would try to bring people together, in controversial and interesting political discussions.
So we asked the readers of ZEIT online, if we could introduce some other reader to them. Those who wanted to participate in the project had to answer at first five yes-no-questions: Has Germany accepted too many refugees? Should Germany abandon the Euro and return to the Deutsche Mark? Is the West treating Russia fairly? Was abandoning nuclear energy the right move? Should homosexual couples be allowed to marry? We then asked for a handful of further informations: email and mobile number, zip code, hobbies and gender, for example.
We then sent a confirmation email and a sms to the mobile number to check validity. If both were correctly answered, we assumed that the recipient really wanted to participate, and started matching.
Since we only had the zip code of each participant (and not the complete address), we estimated the spacial distance between participants by computing the distance between the barycenters of their zip code areas. If this distance was larger than 20 km, we set the distance of these two participants to "minus infinite" -- which meant effectively that we removed the corresponding edge from the emerging graph.
Otherwise, we set the distance (the edge weight) of any pair of persons to the number of differing answers. So if, for instance, person A and B differed in three questions (and answered otherwise the same), they got distance three. We ended with a graph of half a million edges and more than 5500 nodes. In this graph, we computed a maximum weight matching in this graph using the python module networkX. The final result gave us 2700 edges or pairs of people; only a handful could not be matched.
Many of them really met on June 18, 2017, 3 pm. We know, because they told us: in hundreds of enthusiastic emails, with hundreds of selfies.