擅长:python、mysql、java
<p>我将创建一个<code>helper</code>数据框,其中包含所有的年份开始日期,然后过滤出与<code>df</code>中年份匹配的年份,最后将它们合并在一起:</p>
<pre><code># First make sure it is proper datetime
df['asofdate'] = pd.to_datetime(df.asofdate)
# Create your temporary dataframe of year start dates
helper = pd.DataFrame({'asofdate':pd.date_range(df.asofdate.min(), df.asofdate.max(), freq='YS')})
# Filter out the rows where the year is already in df
helper = helper[~helper.asofdate.dt.year.isin(df.asofdate.dt.year)]
# Merge back in to df, sort, and forward fill
new_df = df.merge(helper, how='outer').sort_values('asofdate').ffill()
>>> new_df
asofdate port_id
0 2010-01-01 76.0
1 2010-04-01 43.0
2 2011-02-01 76.0
5 2012-01-01 76.0
3 2013-01-02 93.0
6 2014-01-01 93.0
7 2015-01-01 93.0
8 2016-01-01 93.0
4 2017-02-01 43.0
</code></pre>