Comparing column values based on condition

Question

I have the following output from a txt file. My goal is to find the difference between values of Column 2 and Column 3 as long as the value in Column 1 remains below or equal to 5, that means my expected output is the difference of Column 2 and 3 values up to Row 5 as the Column 1 value in Row 6 is greater than 5.

1. 1 4 5
2. 2 6 7
3. 3 8 8
4. 4 4 7
5. 5 3 2
6. 6 8 4

I tried the following approach.

import pandas as pd
data= pd.read_table('/Users/Hrihaan/Desktop/A.txt', dtype=float, header=None, sep='\s+').values
x=data[:,0]
y=(data[:,1] for x<=5)
z=(data[:,2] for x<=5)
Diff=y-z
print(Diff)

I received this error: (SyntaxError: invalid syntax), any help on how to get it going would be really helpful.

Answer 1

import numpy as np

>>> np.where(data[:, 0] <= 5, data[:, 1] - data[:, 2], np.nan)
array([ -1.,  -1.,   0.,  -3.,  1.,  nan])

For your code, you can use a conditional list comprehension:

y = [i for x, i in zip(data[:, 0], data[:, 1]) if x <= 5]
z = [i for x, i in zip(data[:, 0], data[:, 2]) if x <= 5]
diff = [a - b for a, b in zip(y, z)]

or...

diff = [y - z for x, y, z in data if x <= 5]

Answer 2

Or you can try this

(df2['v2'].subtract(df2['v3']))[(df2['v1']<=5)]

Out[856]: 
0   -1
1   -1
2    0
3   -3
4    1
dtype: int64

Data input

  df2
    Out[857]: 
       v1  v2  v3
    0   1   4   5
    1   2   6   7
    2   3   8   8
    3   4   4   7
    4   5   3   2
    5   6   8   4