问题
I have a dataframe like this:
index S_1 S_2 S_3 S_4
0 1 0 0 1
1 1 1 Nan Nan
I am trying to change it from long to wide. Eg.
index num S
0 1 1
0 2 0
0 3 0
0 4 1
1 1 1
1 2 1
1 3 Nan
1 4 Nan
I have tried the following code, based on this answer, but I get the following error:
matches_df.columns = matches_df.columns.str.split('_', expand=True)
TypeError: object of type 'float' has no len()
Why am I unable to split on the "_"? There is other information in the columns which I would like to preserve.
回答1:
There is pandas.wide_to_long
, which is nice when the columns have stubs like that.
import pandas as pd
df.reset_index(inplace=True,drop=True)
df['id'] = df.index
df = pd.wide_to_long(df, stubnames='S_', i='id', j='num').reset_index().rename(columns={'S_':'S'})
# id num index S
#0 0 1 0 1.0
#1 1 1 1 1.0
#2 0 2 0 0.0
#3 1 2 1 1.0
#4 0 3 0 0.0
#5 1 3 1 NaN
#6 0 4 0 1.0
#7 1 4 1 NaN
来源:https://stackoverflow.com/questions/50087135/convert-dataframe-from-wide-to-long-pandas