Pandas: Combine two dataframe columns in a sorted column

Question

Suppose that I have this dataframe:

import pandas as pd

def creatingDataFrame():

    raw_data = {'Region1': ['A', 'A', 'C', 'B' , 'A', 'B'],
                'Region2': ['B', 'C', 'A', 'A' , 'B', 'A'],
                'var-1': [20, 30, 40 , 50, 10, 20],
                'var-2': [3, 4 , 5, 1, 2, 3]}
    df = pd.DataFrame(raw_data, columns = ['Region1', 'Region2','var-1', 'var-2'])
    return df

I want to generate this column:

df['segment']=['A-B','A-C','A-C','A-B','A-B','A-B']

Note that it is using columns 'Region1' and 'Region2' but in a sorted order. I have no clue how to do that using pandas. The only solution that I have in mind is to use a list as intermediary step:

Regions=df[['Region1','Region2']].values.tolist()
segments=[]
for i in range(np.shape(Regions)[0]):
    auxRegions=sorted(Regions[i][:])
    segments.append(auxRegions[0]+'-'+auxRegions[1])
df['segments']=segments

To get:

>>> df['segments']
0    A-B
1    A-C
2    A-C
3    A-B
4    A-B
5    A-B

Answer 1

You need:

df['segments'] = ['-'.join(sorted(tup)) for tup in zip(df['Region1'], df['Region2'])]

Output:

    Region1 Region2  var-1  var-2 segments
0       A       B     20      3      A-B
1       A       C     30      4      A-C
2       C       A     40      5      A-C
3       B       A     50      1      A-B
4       A       B     10      2      A-B
5       B       A     20      3      A-B

Answer 2

np.sort

v = np.sort(df.iloc[:, :2], axis=1).T
df['segments'] = [f'{i}-{j}' for i, j in zip(v[0], v[1])]  # '{}-{}'.format(i, j)

df
  Region1 Region2  var-1  var-2 segments
0       A       B     20      3      A-B
1       A       C     30      4      A-C
2       C       A     40      5      A-C
3       B       A     50      1      A-B
4       A       B     10      2      A-B
5       B       A     20      3      A-B

---

DataFrame.agg + str.join

df['segments'] = pd.DataFrame(
    np.sort(df.iloc[:, :2], axis=1)).agg('-'.join, axis=1)

df
  Region1 Region2  var-1  var-2 segments
0       A       B     20      3      A-B
1       A       C     30      4      A-C
2       C       A     40      5      A-C
3       B       A     50      1      A-B
4       A       B     10      2      A-B
5       B       A     20      3      A-B

(One above's faster.)