Python3: Loop a numpy array through a function

Question

Let's say I have a numpy array like this (positions_full) which load some coordinate data like 2.5 or 8.2. I now wanted to loop that array through the def isInside. How can I do this?

positions_full = np.loadtxt('positions.txt')

x = positions_full[:,0]

y = positions_full[:,1]  

def isInside(circle_x, circle_y, rad, x, y):

    if ((x - circle_x) * (x - circle_x) +

        (y - circle_y) * (y - circle_y) <= rad * rad):

        return True;

    else:

        return False;


x = 2.5

y = 8.2

circle_x = 0;

circle_y = 5;

rad = 2;

if(isInside(circle_x, circle_y, rad, x, y)):

    print(x,y,rad,"Inside");

else:

    print(x,y,rad,"Outside");

Gabriel Avendaño · Accepted Answer · 2022-02-23 19:09:43Z

1

I think it is better to use numpy's vectorization. You can make your function isInside to return a numpy array of boolean values. Then you can just loop outside of the function with a common for-loop. Something like this:

import numpy as np
positions = np.array([[2.5, 8], [3, 10], [0, 5], [1, 5]])
x = positions[:, 0]
y = positions[:, 1]

def isInside(circle_x, circle_y, rad, x, y):
   return ((x - circle_x) ** 2 + (y - circle_y) ** 2) <= rad ** 2

circle_x = 0;
circle_y = 5;
rad = 2;

for is_inside in isInside(circle_x, circle_y, rad, x, y):
  print ("Inside" if is_inside else "Outside")

answered Feb 23, 2022 at 19:09

Gabriel Avendaño

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2 Comments

Marc Over a year ago

but how is it possible to print the respective x and y coordinates also for each individual "Inside" or "Outside"? To get something like : [2.5, 8] Outside, [3, 10] Outside, [0, 5] Inside, [1, 5] Inside?

Gabriel Avendaño Over a year ago

You can change the for loop so that it has an incremental variable i and then you index the list with this value. For example, first you assign the isInside(...) result to a variable like this is_inside_list = isInside(...) before the for loop, and then change the for to for i in range(len(is_inside_list)). This would iterate i from 0 to lenght of the list. Then you can address inside the values with is_inside_list[i], x[i] and y[i]. Check out this asnwer

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