如何格式化groupby year函数pandas - 返回unicode属性错误

Question

使用下面的代码尝试按年份计算条目数，返回 unicode 值错误。下面的实现有替代方案吗？raw_news_4.groupby(raw_news_4["date_publish"].map(lambda x: x.year))#raw_news_4 sampledate_publish    title213059  2006-10-18 12:47:13 Is God dead Atheism finds a market in     US20559   2006-11-12 13:11:20 WITNESS Waking up paralyzed in Sri     Lankas war zone111765  2007-01-18 23:02:00 AIDS in Americas123806  2007-01-18 23:02:00 Malaria7060    2007-01-18 23:02:00 AIDS pandemic121746  2007-01-18 23:02:00 Indonesia mudflow206142  2007-01-18 23:02:00 Pakistan violence241749  2007-01-18 23:02:00 AttributeError: 'unicode' object has no attribute 'year'