Concatenate string columns and index

Question

I have a DataFrame like this:

A    B
----------
c    d
e    f

I'd like to introduce a third column, made up of a concatenation of A , B and the index, so that the DataFrame becomes:

A    B    C
---------------
c    d    cd0
e    f    ef1

I'd like to do that like so:

df['C'] = df['A'] + df['B'] + # and here I don't know how to reference the row index. 

How can I do this?

Answer 1

Option 1
For better scalability, use assign + agg :

df['C'] = df.assign(index=df.index.astype(str)).agg(''.join, 1)
df

   A  B    C
0  c  d  cd0
1  e  f  ef1

Or, using np.add.reduce in a similar fashion:

df['C'] = np.add.reduce(df.assign(index=df.index.astype(str)), axis=1)
df

   A  B    C
0  c  d  cd0
1  e  f  ef1

---

Option 2
A less scalable option using vectorised string concatenation:

df['C'] = df['A'] + df['B'] + df.index.astype(str)
df

   A  B    C
0  c  d  cd0
1  e  f  ef1

Answer 2

With pd.DataFrame.itertuples
Python 3.6

df.assign(C=[f'{a}{b}{i}' for i, a, b in df.itertuples()])

   A  B    C
0  c  d  cd0
1  e  f  ef1

---

With pd.Series.str.cat

df.assign(C=df.A.str.cat(df.B).str.cat(df.index.astype(str)))

   A  B    C
0  c  d  cd0
1  e  f  ef1

---

Mish/Mash

from operator import add
from functools import reduce
from itertools import chain

df.assign(C=reduce(add, chain((df[c] for c in df), [df.index.astype(str)])))

   A  B    C
0  c  d  cd0
1  e  f  ef1

---

Summation

df.assign(C=df.sum(1) + df.index.astype(str))

   A  B    C
0  c  d  cd0
1  e  f  ef1

Answer 3

df['C'] = df['A'].astype(str) + df['B'].astype(str) + np.array(map(str, df.index.values))

Basically you access the df index with df.index, and to turn that into a numpy array you add the .values, and to convert that into a string (to easily add to the previous columns, which are strings), you can use a map function.

Edit: added .astype(str) to columns A and B, to convert them to strings. If they are already strings, this won't be necessary.