How can I add/distribute the values of one dataframe in other dataframe according to the date in Pandas

Question

I have 2 dataframes:

df1:

df2:

What I need to code is:

If the the Variants in df2 matches with the variants in df1
The qty from df2 of that particular variant should be added to qty of variant in df1
But, the qty should be added to the last date of the month available in df1.

for eg:
In df1 we only have variant A and last date of variant A is 01/31/2022 with qty 2.
In df 2, we have multiple variants. Variant A has the qty 5.

So the new df1 should be:
Variant A on 31st = 5+2 = 7.

Asked By: kanika

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Source

Answer 1

I’ve made a smaller example because I didn’t want to build a full database for you.
The caveats of the solution here is that if you have the main database having no rows for B and C then as seen below they will end up with Nan values. However, if you have rows for variants B and C, it should work.

import pandas as pd
import numpy as np

df1 = pd.DataFrame({"Variant":["A","A","A","A","A"], 
      "Date":["1/27/2022","1/28/2022","1/29/2022","1/30/2022","1/31/2022"],
      "Qty":[0,0,1,2,2]})
df2 = pd.DataFrame({"Variant":["A","B","C"], "Qty":[5,6,7]})
df = pd.merge(df1,df2,how='outer',on=["Variant","Qty"])

  Variant       Date  Qty
0       A  1/27/2022    0
1       A  1/28/2022    0
2       A  1/29/2022    1
3       A  1/30/2022    2
4       A  1/31/2022    2
5       A        NaN    5
6       B        NaN    6
7       C        NaN    7

df["Date"] = df.groupby("Variant")["Date"].transform('ffill')

df
  Variant       Date  Qty
0       A  1/27/2022    0
1       A  1/28/2022    0
2       A  1/29/2022    1
3       A  1/30/2022    2
4       A  1/31/2022    2
5       A  1/31/2022    5
6       B        NaN    6
7       C        NaN    7

We ca now group by variant and date and just sum the values. Then delete duplicate rows.

df["Qty"] = df.groupby(["Variant","Date"])["Qty"].transform('sum')
df = df.drop_duplicates()

Out[25]: 
  Variant       Date  Qty
0       A  1/27/2022  0.0
1       A  1/28/2022  0.0
2       A  1/29/2022  1.0
3       A  1/30/2022  2.0
4       A  1/31/2022  7.0
6       B        NaN  NaN
7       C        NaN  NaN

Answered By: Vikram Raghu

How can I add/distribute the values of one dataframe in other dataframe according to the date in Pandas

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