Pandas - add multiple values to row inside while loop

Question

I'm working with a dataframe inside a while loop that needs to be updated based on the simulation time. Here's an example:

import pandas as pd
import random

n = 0
df = pd.DataFrame(columns=['A', 'B'])

while n < 10:
  df = df.append({'A': random.uniform(0, 1), 'B': random.uniform(0, 1)}, 
                 ignore_index=True)
  df = df.append({'A': random.uniform(0, 1), 'B': random.uniform(0, 1)}, 
                 ignore_index=True)

  df['New Column'] = n

  print('This value should be added to the new rows only ' + str(n))
  n += 1
  print(df)

This results in the entire new column being updated at once, which is undesired in my case. Here are the first three prints:

This value should be added to the new rows only 0
          A         B  New Column
0  0.242312  0.369978           0
1  0.709112  0.650794           0
This value should be added to the new rows only 1
          A         B  New Column
0  0.242312  0.369978           1    <- should have been 0
1  0.709112  0.650794           1    <- should have been 0
2  0.293787  0.229019           1
3  0.828184  0.917984           1
This value should be added to the new rows only 2
          A         B  New Column
0  0.242312  0.369978           2    <- should have been 0
1  0.709112  0.650794           2    <- should have been 0
2  0.293787  0.229019           2    <- should have been 1
3  0.828184  0.917984           2    <- should have been 1
4  0.644289  0.589050           2
5  0.371361  0.759865           2

Can I do this in one operation or I need to copy to another dataframe and then append that?

U13-Forward · Accepted Answer · 2019-07-11 02:07:11Z

1

Use the below code:

import pandas as pd
import random

n = 0
df = pd.DataFrame(columns=['A', 'B', 'New Column'])

while n < 10:
  df = df.append({'A': random.uniform(0, 1), 'B': random.uniform(0, 1), 'New Column': n}, 
                 ignore_index=True)
  df = df.append({'A': random.uniform(0, 1), 'B': random.uniform(0, 1), 'New Column': n}, 
                 ignore_index=True)

  print('This value should be added to the new rows only ' + str(n))
  n += 1
  print(df)

Simply just have a New Column from the beginning, and then add the value just like you do with A and B inside the append, I am making New Column also in the same appends.

Your code doesn't work since you're modifying all values on every loop occasion, when you need it for the appended dataframe, which is what I'm doing.

edited Jul 11, 2019 at 2:07

answered Jul 11, 2019 at 1:55

U13-Forward

71.8k15 gold badges100 silver badges125 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Pandas - add multiple values to row inside while loop

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related