index match in Python

Question

I have the following dataframe

value	A	B
1.0	7.0	8.0
2.0	9.0	8.8
3.0	9.5	9.1
4.0	10.0	9.4
5.0	13.0	8.4
6.0	15.0	8.5

What I'm attempting to do:

example:

I'm thinking some sort of if/else statetement:

    -if 
        A < B
    return 1.0 ==> since A=7.0 < B=8.0
    -else: 
        if A > B
         look at the closest values from B column that match the target value A.
         Let's say the value A=9.0 so in this example it's going to be 8.8 and 9.1. 
         I need to take the larger number out of these 2 and return the 
         corresponding value from value column. 
         So in this case it'd return 3.0.

I tried using numpy for this, and indexing it... np.where looked promising but I keep getting stuck in the second part. Can anyone help? It's safe to assume that the values are sorted in the ascending order.

Answer 1

I'm sorry to say it, but your question is not clear at all. You made strange mistakes and did not explain clearly what you wanted.

So, what this program does:

1. If A < B, return "value" from the same line;
2. If A > B, looks through the whole dataframe from the current B up to the end and takes "value" from the first line where B is more than A.

If it is not what you wanted, please, give more clear explanation) Delighted to help you.

import pandas as pd
df = pd.DataFrame({
               "value": [1., 2., 3., 4., 5., 6], 
               'A': [7., 9., 9.5, 10., 13., 15.],
               'B': [8., 8.8, 9.1, 9.4, 8.4, 8.5]
             })
for i in range(df.shape[0]):
    if df['A'][i] < df['B'][i]: 
        print(df["value"][i])
    else:
        for j in range(i, df.shape[0]):
            if df['A'][i] < df['B'][j]:
                print(df["value"][j])

Edited: output is 1.0, 3.0, 4.0. I've just seen that you noticed your signs, sorry)