pandas dataframe concatenate strings from a subset of columns and put them into a list

Question

I tried to retrieve strings from a subset of columns from a DataFrame, concatenate the strings into one string, and then put these into a list,

# row_subset is a sub-DataFrame of some DataFrame
sub_columns = ['A', 'B', 'C']
string_list = [""] * row_subset.shape[0]
for x in range(0, row_subset.shape[0]):
    for y in range(0, len(sub_columns)):
        string_list[x] += str(row_subset[sub_columns[y]].iloc[x])

so the result is like,

['row 0 string concatenation','row 1 concatenation','row 2 concatenation','row3 concatenation']

I am wondering what is the best way to do this, more efficiently?

jezrael · Accepted Answer · 2017-08-18 11:48:43Z

4

I think you need select columns by subset by [] first and then sum or if need separator use join:

df = pd.DataFrame({'A':list('abcdef'),
                   'B':list('qwerty'),
                   'C':list('fertuj'),
                   'D':[1,3,5,7,1,0],
                   'E':[5,3,6,9,2,4],
                   'F':list('aaabbb')})

print (df)
   A  B  C  D  E  F
0  a  q  f  1  5  a
1  b  w  e  3  3  a
2  c  e  r  5  6  a
3  d  r  t  7  9  b
4  e  t  u  1  2  b
5  f  y  j  0  4  b

sub_columns = ['A', 'B', 'C']
print (df[sub_columns].sum(axis=1).tolist())
['aqf', 'bwe', 'cer', 'drt', 'etu', 'fyj']

print (df[sub_columns].apply(' '.join, axis=1).tolist())
['a q f', 'b w e', 'c e r', 'd r t', 'e t u', 'f y j']

Very similar numpy solution:

print (df[sub_columns].values.sum(axis=1).tolist())
['aqf', 'bwe', 'cer', 'drt', 'etu', 'fyj']

edited Aug 18, 2017 at 11:48

answered Aug 18, 2017 at 11:43

jezrael

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