Set index by date and groupby gives only NaNs-CodePudding

I have the following df. As you can see there may be multiple prices per token from the same day. So I want to take the median day price.

    token_address                                date       close
0   0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48  2021-08-18  1.078874e-07
1   0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48  2021-08-18  1.088589e-07
2   0xa80f2c8f61c56546001f5fc2eb8d6e4e72c45d4c  2021-08-18  2.835567e-07
3   0xbbc2ae13b23d715c30720f079fcd9b4a74093505  2021-08-18  1.633322e-06
4   0xd2877702675e6ceb975b4a1dff9fb7baf4c91ea9  2021-08-18  3.201045e-06
...

So I did the following

df['date'] = pd.to_datetime(df['date'])
df['median'] = df.set_index('date').groupby('token_address')['close'].median()

but somehow i get NaNs?

    token_address   date    close   median
0   0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48  2021-08-18  1.078874e-07    NaN
1   0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48  2021-08-18  1.088589e-07    NaN
2   0xa80f2c8f61c56546001f5fc2eb8d6e4e72c45d4c  2021-08-18  2.835567e-07    NaN
3   0xbbc2ae13b23d715c30720f079fcd9b4a74093505  2021-08-18  1.633322e-06    NaN
4   0xd2877702675e6ceb975b4a1dff9fb7baf4c91ea9  2021-08-18  3.201045e-06    NaN

CodePudding user response：

try this out

in your attempt above, the groupby results (having fewer rows) don't match with the count of df rows, hence the error.

Transform applies the grouped value to all rows that makes up the group

df['median'] = df.groupby(['token_address','date'])['close'].transform('median')
df

token_address   date    close   median
0   0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48  2021-08-18  1.078874e-07    1.083732e-07
1   0xa0b86991c6218b36c1d19d4a2e9eb0ce3606eb48  2021-08-18  1.088589e-07    1.083732e-07
2   0xa80f2c8f61c56546001f5fc2eb8d6e4e72c45d4c  2021-08-18  2.835567e-07    2.835567e-07
3   0xbbc2ae13b23d715c30720f079fcd9b4a74093505  2021-08-18  1.633322e-06    1.633322e-06
4   0xd2877702675e6ceb975b4a1dff9fb7baf4c91ea9  2021-08-18  3.201045e-06    3.201045e-06