extracting value from pandas dataframe in reference to other values

Question

I have a dataframe:

d= {'page_number':[0,0,0,0,0,0,1,1,1,1], 'text':[aa,ii,cc,dd,ee,ff,gg,hh,ii,jj]}
df = pd.DataFrame(data=d)
df
 
   page_number   text
0     0           aa
1     0           ii
2     0           cc
3     0           dd
4     0           ee
5     0           ff
6     1           gg
7     1           hh
8     1           ii
9     1           jj

I want to spot the page_numer where 'gg' appears, now on the same page_number there can be many different substrings, but I'm interested in extracting the row number of where 'ii' appears on the same page_number of 'gg' (not interested in getting results of other 'ii' substrings appearances)

idx=np.where(df['text'].str.contains(r'gg', na=True))[0][0]

won't necessarily help here as it retrieves the row number of 'gg' but not its 'page_number'.

Many thanks

Answer 1

You first leave only 'ii' and 'gg' appearances:

df = df[df['text'].isin(['ii', 'gg'])

Then by groupby page number we can assume that when ever we got 2 then they are on the same page:

df2 = df.groupby('page_number').count()
df2[df2['text'] == 2]

Answer 2

You can use pandas to retrieve column value on the basis of another column value. I hope this will retrieve what you are looking for. df[df['text']=='gg']['page_number']

Answer 3

In case you have several 'gg's and 'ii's on any page:

This will return a boolean Series:

df = df.groupby(by='page_number').agg(lambda x: True if 'gg' in x.values 
                                      and 'ii' in x.values else False)

And this will get you the numbers of pages

df[df.text].index