How to add new column from another dataframe according the dates in pandas

Question

I have two dataframes like these,
df1:

|    A     |    B     |    Date     |   
| -------- | -------- |-------------|
|    x     |    a     |  03-10-2022 |
|    y     |    b     |  02-10-2022 | 
|    z     |    c     |  01-10-2022 |
|    t     |    d     |  30-09-2022 |
|    k     |    e     |  29-09-2022 |
|    h     |    f     |  28-09-2022 |
|    u     |    g     |  27-09-2022 |

df2:

|   unnamed      |    14-10-2022  |  07-10-2022  |  30-09-2022  |  23-09-2022  |
| -------------  | -------------- |--------------|------------- |------------- |
|     x          |        a       |      aa      |     aaa      |    aaaa      |
|     y          |        b       |      bb      |     bbb      |    bbbb      |
|    rates       |       30.2     |     24.8     |    27.6      |    33.1      |
|     z          |        c       |      cc      |     ccc      |    cccc      |

In df1 the dates are going as days and days but df2 the dates are going to weekly.
I would like to add rates row in df2 to df1 as a column but according dates. For example between 14-10-2022 and 07-10-2022 rates are must be 24.8

I am expecting like this:

|    A     |    B     |    Date     |     Rates  |
| -------- | -------- |-------------|------------|
|    x     |    a     |  03-10-2022 |     27.6   |
|    y     |    b     |  02-10-2022 |     27.6   | 
|    z     |    c     |  01-10-2022 |     27.6   | 
|    t     |    d     |  30-09-2022 |     27.6   | 
|    k     |    e     |  29-09-2022 |     33.1   |
|    h     |    f     |  28-09-2022 |     33.1   | 
|    u     |    g     |  27-09-2022 |     33.1   |

How can I do this?

Asked By: Scn

||

Source

Answer 1

Use merge_asof with filtering df2 for row with rates:

df1['Date'] = pd.to_datetime(df1['Date'], dayfirst=True)
df1 = df1.sort_values('Date')

df22 = df2.set_index('unnamed')
df22.columns = pd.to_datetime(df22.columns, dayfirst=True)
df22 = df22.loc['rates'].to_frame('Rates').sort_index()

df = pd.merge_asof(df1, df22, left_on='Date', right_index=True).sort_index()
print (df)
   A  B       Date Rates
0  x  a 2022-10-03  27.6
1  y  b 2022-10-02  27.6
2  z  c 2022-10-01  27.6
3  t  d 2022-09-30  27.6
4  k  e 2022-09-29  33.1
5  h  f 2022-09-28  33.1
6  u  g 2022-09-27  33.1

Answered By: jezrael

How to add new column from another dataframe according the dates in pandas

Question:

Answers: