Python cookbook(数据结构与算法)根据字段将记录分组操作示例

rows = [  {'address': '5412 N CLARK', 'date': '07/01/2012'},  {'address': '5148 N CLARK', 'date': '07/04/2012'},  {'address': '5800 E 58TH', 'date': '07/02/2012'},  {'address': '2122 N CLARK', 'date': '07/03/2012'},  {'address': '5645 N RAVENSWOOD', 'date': '07/02/2012'},  {'address': '1060 W ADDISON', 'date': '07/02/2012'},  {'address': '4801 N BROADWAY', 'date': '07/01/2012'},  {'address': '1039 W GRANVILLE', 'date': '07/04/2012'},]from operator import itemgetterfrom itertools import groupbyrows.sort(key=itemgetter('date')) #首先以date字段进行排序for date, items in groupby(rows, key=itemgetter('date')): #再以date进行分组  print(date)  for i in items:    print('  ', i)# 如果只是简单地根据日期将数据分组到一起，放进一个大的数据结构中以允许进行随机访问，那么可以利用defaultdict构建一个一键多值的字典会更好#Example of building a multidictfrom collections import defaultdictrows_by_date = defaultdict(list) #创建一个一键多值的字典，for row in rows:  rows_by_date[row['date']].append(row)for r in rows_by_date['07/01/2012']:  print(r)

07/01/2012   {'address': '5412 N CLARK', 'date': '07/01/2012'}   {'address': '4801 N BROADWAY', 'date': '07/01/2012'}07/02/2012   {'address': '5800 E 58TH', 'date': '07/02/2012'}   {'address': '5645 N RAVENSWOOD', 'date': '07/02/2012'}   {'address': '1060 W ADDISON', 'date': '07/02/2012'}07/03/2012   {'address': '2122 N CLARK', 'date': '07/03/2012'}07/04/2012   {'address': '5148 N CLARK', 'date': '07/04/2012'}   {'address': '1039 W GRANVILLE', 'date': '07/04/2012'}{'address': '5412 N CLARK', 'date': '07/01/2012'}{'address': '4801 N BROADWAY', 'date': '07/01/2012'}