A few weeks ago I wrote about ranking Champions League teams using the Elo Rating algorithm, and since I wrote that post I’ve collated data for 10 years worth of matches so I thought an update was in order.

After extracting the details of all those matches I saved them to a JSON file so that I wouldn’t have to parse the HTML pages every time I tweaked the algorithm. This should also make it easier for other people to play with the data.

I described the algorithm in the previous post and had analysed the rankings for one season. However, it was difficult to understand why teams has been ranked in a certain order so I drilled into the data to find out.

Since the 2012/2013 season is the freshest in my memory I started with that.

The first thing to do was load the matches from disk: _~lisp (ns ranking-algorithms.uefa (:require [clj-time.format :as f]) (:require [clojure.data.json :as json])) (defn as-date [date-field] (f/parse (f/formatter "dd MMM YYYY") date-field )) (defn date-aware-value-reader [key value] (if (= key :date) (as-date value) value)) (defn read-from-file [file] (json/read-str (slurp file) :value-fn date-aware-value-reader :key-fn keyword)) _~

I’ve written previously about reifying a date masquerading as a string but for now we want to give those matches a name and then process them. _~lisp > (def the-matches (read-from-file "data/cl-matches-2013.json")) #'ranking-algorithms.uefa/the-matches > (count the-matches) 213 _~

I already had a function https://github.com/mneedham/ranking-algorithms/blob/27f94ccf1fc6c63663c8b3d512a2470330585803/src/ranking_algorithms/core.clj#L28 which would apply the Elo algorithm across the matches, but since I wanted to drill into each team’s performance I wrapped that function in another one called https://github.com/mneedham/ranking-algorithms/blob/27f94ccf1fc6c63663c8b3d512a2470330585803/src/ranking_algorithms/core.clj#L121: _~lisp (comment "other functions excluded for brevity") (defn format-for-printing [all-matches idx [team ranking & [rd]]] (let [team-matches (show-matches team all-matches)] (merge {:rank (inc idx) :team team :ranking ranking :rd rd :round (performance team-matches)} (match-record team-matches)))) (defn print-top-teams ([number all-matches] (print-top-teams number all-matches {})) ([number all-matches base-rankings] (clojure.pprint/print-table [:rank :team :ranking :round :wins :draw :loses] (map-indexed (partial format-for-printing all-matches) (top-teams number all-matches base-rankings))))) _{~ ~}lisp > (ranking-algorithms.core/print-top-teams 10 the-matches) ======================================================================== :rank | :team | :ranking | :round | :wins | :draw | :loses ======================================================================== 1 | Bayern | 1272.74 | Final | 10 | 1 | 2 2 | PSG | 1230.02 | Quarter-finals | 6 | 3 | 1 3 | Dortmund | 1220.96 | Final | 7 | 4 | 2 4 | Real Madrid | 1220.33 | Semi-finals | 6 | 3 | 3 5 | Porto | 1216.97 | Round of 16 | 5 | 1 | 2 6 | CFR Cluj | 1216.56 | Group stage | 7 | 1 | 2 7 | Galatasaray | 1215.56 | Quarter-finals | 5 | 2 | 3 8 | Juventus | 1214.0 | Quarter-finals | 5 | 3 | 2 9 | Málaga | 1211.53 | Quarter-finals | 5 | 5 | 2 10 | Valencia | 1211.0 | Round of 16 | 4 | 2 | 2 ======================================================================== _~

I’ve excluded most of the functions but you can find the source in core.clj on github.

Clojure-wise I learnt about the http://clojuredocs.org/clojure_core/clojure.pprint/print-table function which came in handy and Elo-wise I realised that the ranking places a heavy emphasis on winning matches.

If you follow the Champions League closely you’ll have noticed that Barcelona are missing from the top 10 despite reaching the Semi Final. The Elo algorithm actually ranks them in 65th position: _~lisp ========================================================================================= :rank | :team | :ranking | :round | :wins | :draw | :loses ========================================================================================= 63 | Motherwell | 1195.04 | Third qualifying round | 0 | 0 | 2 64 | Feyenoord | 1195.04 | Third qualifying round | 0 | 0 | 2 65 | Barcelona | 1194.68 | Semi-finals | 5 | 3 | 4 66 | BATE | 1194.36 | Group stage | 5 | 3 | 4 67 | Anderlecht | 1193.41 | Group stage | 4 | 2 | 4 ========================================================================================= _~