Python-我想使用pandas将第二行的列移动到第一行列

Question

I have csv data like this

column1 column2 
A       12
A       13
B       15
B       16
C       12
C       14

I want to merge rows with same value in column 1 by creating another column3 or say transpose like this

column1 column2 column3
A       12      13
B       15      16
C       12      14

I'm using pandas and want to run some loop for this, probably.

Answer 1

use groupby with cumcount to set an index then unstack

c = 'column1'
s = df.set_index([c, df.groupby(c).cumcount() + 2]).column2
s.unstack().add_prefix('column').reset_index()

  column1  column2  column3
0       A       12       13
1       B       15       16
2       C       12       14

---

This will handle if there are uneven numbers of groups as well.

Consider the df

column1 column2 
A       12
A       13
B       15
B       16
B       16
C       12
C       14
C       14
C       14

Then

c = 'column1'
s = df.set_index([c, df.groupby(c).cumcount() + 2]).column2
s.unstack().add_prefix('column').reset_index()

  column1  column2  column3  column4  column5
0       A     12.0     13.0      NaN      NaN
1       B     15.0     16.0     16.0      NaN
2       C     12.0     14.0     14.0     14.0

---

If you wanted to fill those NaN ahead of time, use the fill_value parameter in unstack

c = 'column1'
s = df.set_index([c, df.groupby(c).cumcount() + 2]).column2
s.unstack(fill_value=0).add_prefix('column').reset_index()


  column1  column2  column3  column4  column5
0       A       12       13        0        0
1       B       15       16       16        0
2       C       12       14       14       14