逐行加入两个 pandas dataframe 列

Question

Assuming I have a pandas dataframe df , whereby df is:

    vaccine       age           height
0   pfizer       48.0            181.0
1   moderna      81.0            175.0
2   moderna      27.0            190.4
3   moderna      64.0            178.5

I am trying to join the two columns (age, height) into a single column row-wise, whereby age and height are grouped by their respective vaccine.

Basically, I am trying to get:

   vaccine        new_col     
0   pfizer         48.0
1   pfizer         181.0
2   moderna        81.0         
3   moderna        175.0
4   moderna         27.0             
5   moderna        190.4
6   moderna         64.0
7   moderna        178.5

I have unsuccessfully tried using pd.concat, df.merge, etc. I am not familiar with any pandas function that does this. I also tried using the apply function but I wasn't successful.

Answer 1

First set the index as vaccine then stack the dataframe, and drop index level at 1, finally reset the index.

df.set_index('vaccine').stack().droplevel(1).to_frame('new_col').reset_index()

   vaccine  new_col
0   pfizer     48.0
1   pfizer    181.0
2  moderna     81.0
3  moderna    175.0
4  moderna     27.0
5  moderna    190.4
6  moderna     64.0
7  moderna    178.5