How can I lowercase substrings in pandas data frame?

user_11601412 0
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I have a Pandas data frame like this one

String = ["".join(np.random.choice(list("PQRSTUVXYZ"), size=7)) for _ in range(7)]
Position = np.random.randint(2,7, size = 7)
df=pd.DataFrame((String,Position)).T

I would like to apply the lower() function JUST in the letter which the index is column Position.

I've tried:

df = df[0][df[1]].str.lower()

But it is lowering the whole string.

Thanks for your help!

pandas python string
2 Answers

here is a list comprehension with slice and slice_replace:

df['new'] = ([df[0].str.slice_replace(
             i,i+1,df[0].str.slice(i,i+1).iloc[e].lower()).iloc[e] 
             for e,i in enumerate(df[1])])

         0  1      new
0  TZPVTRT  2  TZpVTRT
1  VSSXYUP  3  VSSxYUP
2  YUTXTQS  2  YUtXTQS
3  SZRURSU  5  SZRURsU
4  XRXQVUP  3  XRXqVUP
5  PSQZZVV  6  PSQZZVv
6  XYYXPYV  3  XYYxPYV

note if your index starts from 1 and not 0 , replace df[0].str.slice(i,i+1) with df[0].str.slice(i-1,i)

user_98406370

You can index the strings. Index up to the lower character, turn that character to lower, and then add everything left over. Really nothing too different from using Series.str.slice_replace, but perhaps a bit more readable. 

df['new_str'] = [s[:i] + s[i].lower() + s[i+1:] for s,i in zip(df[0], df[1])]

         0  1  new_str
0  TTTQTYT  3  TTTqTYT
1  USRRUZS  2  USrRUZS
2  PPXQZZT  6  PPXQZZt
3  UZZVQRQ  3  UZZvQRQ
4  ZVUQPUV  6  ZVUQPUv
5  TRPPSVU  5  TRPPSvU
6  YYZPURQ  5  YYZPUrQ
user_43333590
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