pythonpandasdataframerowffill

Dataframe fill column with previous value until condition

I have a dataframe that looks like this:

Step Text Parameter
15 print 1
16 control 2
17 printout 3
18 print2 1
19 Nan 2
20 Nan 3
21 Nan 4
22 Nan 1
23 Nan 2
24 Nan 1

And I want my dataframe to look like this:

Step Text Parameter
15 print 1
15 print 2
15 print 3
16 control 1
16 control 2
17 control 3
17 control 4
18 printout 1
18 printout 2
19 print2 1

So basically when I have "1" in Parameter column, I need the next value from Step and Text. Any ideas?:)

Solution

  • You can use repeat on a custom group:

    # ensure NaN
df['Text'] = df['Text'].replace('Nan', pd.NA)

# get the number of rows per group starting with 1
n = df.groupby(df['Parameter'].eq(1).cumsum()).size()

# repeat the index of the non NaN values as many times
idx = df['Text'].dropna().index.repeat(n)

# replace the values ignoring the index
# (using the underlying numpy array)
df[['Step', 'Text']] = df.loc[idx, ['Step', 'Text']].to_numpy()

    output:

      Step      Text  Parameter
0   15     print          1
1   15     print          2
2   15     print          3
3   16   control          1
4   16   control          2
5   16   control          3
6   16   control          4
7   17  printout          1
8   17  printout          2
9   18    print2          1