According to the article, the original data was provided by the AMS. I don't think that the AMS leaves this sort of data lying around on laptops on trains, so do to it again you'd have to go and ask them. I suspect that, quite reasonably, the AMS likes to know what uses their data is put to.
On the other hand, data can be mined very easily from the arXiv via the API. I don't know if arXiv data would suffice for you. If so, a little scripting showed the following data for the month of October:
math.CO: 36, 38, 11, 7, 2, 1
math.CA: 9, 11, 5, 1, 1
math.CT: 4, 4, 3
math.GN: 6, 7, 2
math.AT: 18, 9, 2
math.AC: 6, 9, 4, 2
math.CV: 24, 16, 1
math.OC: 6, 11, 5, 3
math.MG: 7, 7, 4, , 1
math.HO: 14
math.DG: 43, 48, 16, 3, 1
math.LO: 9, 2, 2
math.RA: 12, 11, 7, , , 2
math.ST: 3, 14, 2
math.PR: 43, 45, 25, 7
math.GT: 29, 22, 4, 2
math.SG: 13, 4, 2
math.GM: 8
math.SP: 7, , 4, 1
math.FA: 22, 18, 9, 4
math.OA: 9, 6, 4, 3, 1
math-ph: 52, 53, 15, 2, 1
math.DS: 23, 17, 9, 2, 1
math.QA: 13, 13, 3
math.KT: 3, 1
math.GR: 17, 27, 3, 2
math.NA: 4, 13, 9
math.RT: 28, 14, 3
math.NT: 48, 31, 8, , , 1
math.AP: 49, 59, 29, 4
math.AG: 69, 34, 11, 1, 2
Total: 634, 544, 202, 44, 10, 4
Average: 0.44, 0.37, 0.14, 0.03, 0, 0
The ordering is by number-of-authors. So for math.KT there were 4 papers, of which 3 were single authored and 1 with 2 authors. Missing entries are 0s (so in math.NT there was a 6-author paper but none with 4 or 5). So collaborations outweigh single-author papers by a little bit (technical term).
Best Answer
My quick thoughts on the topic:
Most of the papers are not written carefully. Here are my major complains that apply to many (if not to most) of the papers that I have seen:
I think it is extremely rude and unprofessional to write papers in the manner described above. This are some of the reasons why:
By writing a paper the author should (in my opinion):
In my own practice I do my best to follow the rules above. Whether I am successful or not, others will judge.