Based on some rules, how to expand data in Pandas? - pandas

Question

Please forgive my English. I hope I can say clearly.
Assume we have this data:
>>> data = {'Span':[3,3.5], 'Low':[6.2,5.16], 'Medium':[4.93,4.1], 'High':[3.68,3.07], 'VeryHigh':[2.94,2.45], 'ExtraHigh':[2.48,2.06], '0.9':[4.9,3.61], '1.5':[3.23,2.38], '2':[2.51,1.85]}
>>> df = pd.DataFrame(data)
>>> df
Span Low Medium High VeryHigh ExtraHigh 0.9 1.5 2
0 3.0 6.20 4.93 3.68 2.94 2.48 4.90 3.23 2.51
1 3.5 5.16 4.10 3.07 2.45 2.06 3.61 2.38 1.85
I want to get this data:
Span Wind Snow MaxSpacing
0 3.0 Low 0.0 6.20
1 3.0 Medium 0.0 4.93
2 3.0 High 0.0 3.68
3 3.0 VeryHigh 0.0 2.94
4 3.0 ExtraHigh 0.0 2.48
5 3.0 0 0.9 4.90
6 3.0 0 1.5 3.23
7 3.0 0 2.0 2.51
8 3.5 Low 0.0 5.16
9 3.5 Medium 0.0 4.10
10 3.5 High 0.0 3.07
11 3.5 VeryHigh 0.0 2.45
12 3.5 ExtraHigh 0.0 2.06
13 3.5 0 0.9 3.61
14 3.5 0 1.5 2.38
15 3.5 0 2.0 1.85
The principles apply to df:
Span expands by the combination of Wind and Snow to get the MaxSpacing
Wind and Snow is mutually exclusive. When Wind is one of 'Low', 'Medium', 'High', 'VeryHigh', 'ExtraHigh', Snow is zero; when Snow is one of 0.9, 1.5, 2, Wind is zero.
Please help. Thank you.

Answer 1

Use DataFrame.melt for unpivot and then sorting by indices, create Snow column by to_numeric and Series.fillna in DataFrame.insert and last set 0 for Wind column:
df = (df.melt('Span', ignore_index=False, var_name='Wind', value_name='MaxSpacing')
.sort_index(ignore_index=True))
s = pd.to_numeric(df['Wind'], errors='coerce')
df.insert(2, 'Snow', s.fillna(0))
df.loc[s.notna(), 'Wind'] = 0
print (df)
Span Wind Snow MaxSpacing
0 3.0 Low 0.0 6.20
1 3.0 Medium 0.0 4.93
2 3.0 High 0.0 3.68
3 3.0 VeryHigh 0.0 2.94
4 3.0 ExtraHigh 0.0 2.48
5 3.0 0 0.9 4.90
6 3.0 0 1.5 3.23
7 3.0 0 2.0 2.51
8 3.5 Low 0.0 5.16
9 3.5 Medium 0.0 4.10
10 3.5 High 0.0 3.07
11 3.5 VeryHigh 0.0 2.45
12 3.5 ExtraHigh 0.0 2.06
13 3.5 0 0.9 3.61
14 3.5 0 1.5 2.38
15 3.5 0 2.0 1.85
Alternative solution with DataFrame.set_index and DataFrame.stack:
df = df.set_index('Span').rename_axis('Wind', axis=1).stack().reset_index(name='MaxSpacing')
s = pd.to_numeric(df['Wind'], errors='coerce')
df.insert(2, 'Snow', s.fillna(0))
df.loc[s.notna(), 'Wind'] = 0
print (df)
Span Wind Snow MaxSpacing
0 3.0 Low 0.0 6.20
1 3.0 Medium 0.0 4.93
2 3.0 High 0.0 3.68
3 3.0 VeryHigh 0.0 2.94
4 3.0 ExtraHigh 0.0 2.48
5 3.0 0 0.9 4.90
6 3.0 0 1.5 3.23
7 3.0 0 2.0 2.51
8 3.5 Low 0.0 5.16
9 3.5 Medium 0.0 4.10
10 3.5 High 0.0 3.07
11 3.5 VeryHigh 0.0 2.45
12 3.5 ExtraHigh 0.0 2.06
13 3.5 0 0.9 3.61
14 3.5 0 1.5 2.38
15 3.5 0 2.0 1.85