如果同一行的另一列中存在空值，则将列值与前一行合并

Question

I have a data frame like this,

df:

col1      col2       col3
 1        cat          4
nan       dog         nan 
 3        tiger         3
 2        lion          9
 nan      frog         nan
 nan     elephant      nan

I want to create a data frame from this data frame that id there is nan values in col1, col2 values will be added to the previous row value.

for example the desired output data frame will be:

col1     col2             col3
 1      catdog             4
 3       tiger             3
 2     lionfrogelephant    9

How to do this using pandas ?

Answer 1

Use forward filling missing values and aggregate join :

cols = ['col1','col3']
df[cols] = df[cols].ffill()
df = df.groupby(cols)['col2'].apply(''.join).reset_index()
print (df)
   col1  col3              col2
0   1.0   4.0            catdog
1   2.0   9.0  lionfrogelephant
2   3.0   3.0             tiger

Or if necessary forward filling missing values in all columns:

df = df.ffill().groupby(['col1','col3'])['col2'].apply(''.join).reset_index()
print (df)
   col1  col3              col2
0   1.0   4.0            catdog
1   2.0   9.0  lionfrogelephant
2   3.0   3.0             tiger