Select rows in Pandas which does not contain a specific character

Question

I need something similar to

.str.startswith() 
.str.endswith()

but for the middle part of a string.

For example, given the following pd.DataFrame

      str_name
   0    aaabaa
   1    aabbcb
   2    baabba
   3    aacbba
   4    baccaa
   5    ababaa

I need to throw rows 1, 3 and 4 which contain (at least one) letter 'c'.
The position of the specific letter ('c') is not known.
The task is to remove all rows which do contain at least one specific letter

Answer 1

You want df['string_column'].str.contains('c')

>>> df
  str_name
0   aaabaa
1   aabbcb
2   baabba
3   aacbba
4   baccaa
5   ababaa
>>> df['str_name'].str.contains('c')
0    False
1     True
2    False
3     True
4     True
5    False
Name: str_name, dtype: bool

Now, you can "delete" like this

>>> df = df[~df['str_name'].str.contains('c')]
>>> df
  str_name
0   aaabaa
2   baabba
5   ababaa
>>>

Edited to add:

If you only want to check the first k characters, you can slice. Suppose k=3:

>>> df.str_name.str.slice(0,3)
0    aaa
1    aab
2    baa
3    aac
4    bac
5    aba
Name: str_name, dtype: object
>>> df.str_name.str.slice(0,3).str.contains('c')
0    False
1    False
2    False
3     True
4     True
5    False
Name: str_name, dtype: bool

Note, Series.str.slice does not behave like a typical Python slice.

Answer 2

you can use numpy

df[np.core.chararray.find(df.str_name.values.astype(str), 'c') < 0]

  str_name
0   aaabaa
2   baabba
5   ababaa