Ways by node

graph.clj

(defn ways-by-node [ways]
  (reduce
   (partial merge-with (comp vec concat))
   (for [way ways, id (:nodes way)]
     (hash-map id [(:id way)]))))

graph.py

import collections

def ways_by_node(ways):
    ret = collections.defaultdict(list)
    for way in ways:
        way_id = way['id']
        for node_id in way['nodes']:
            ret[node_id].append(way_id)
    return ret