熊猫数据框合并/链接值

Question

I have 2 dataframes df1 and df2. Df1 contains date, date_block_num, item_id, item_cnt_day and has autoincreasing int index. Df2 contains columns with dates such as 2013-01-01, 2013-01-02 and has item_id for index, I have initiallized it with zeros.

My problem is that I want df2 to be filled with item_cnt_day values on the right item_id and date. There are also missing dates from df1 because there are days that nothing was sold.

print(df1)

              date  date_block_num  item_id  item_cnt_day
1       2013-01-03               0     2552           1.0
2       2013-01-05               0     2552           2.0
3       2013-01-06               0     2554           1.0
4       2013-01-15               0     2555           5.0
5       2013-01-10               0     2564           1.0
6       2013-01-02               0     2565           4.0
7       2013-01-04               0     2572           1.0

[186104 rows x 4 columns]


print(df2)

       2013-01-01  2013-01-02     ...      2015-10-30  2015-10-31
5652            0           0     ...               0           0
13071           0           0     ...               0           0
5671            0           0     ...               0           0
5672            0           0     ...               0           0
6675            0           0     ...               0           0
1514            0           0     ...               0           0
2331            0           0     ...               0           0
4271            0           0     ...               0           0

[198 rows x 1034 columns]

Answer 1

I believe you need pivot with reindex if second DataFrame is filled by 0 only:

df = (df1.pivot('item_id','date','item_cnt_day')
         .reindex(index=df2.index, columns=df2.columns)
         .fillna(0))