Python - Write Co-ordinates into array

Question

I was wondering how best to write x,y co-ordinates into an array?

I also don't know how big the array will become...

Or perhaps, is there another data structure that would be easier to use?

Thanks for your help.

Solution 1

You can insert a tuple (X,Y) containing the x,y coordinates into a list.

>>>l=[]
>>>coords = tuple([2,4])
>>>l.append(coords)
>>>l
[(2,3)]

Solution 2

You can use the tuple and list types:

my_coords = [(1, 2), (3, 4)]
my_coords.append((5, 6))
for x, y in my_coords:
    print(x**2 + y**2)

Some examples for coordinates

Points inside unit circle

my_coords = [(0.5, 0.5), (2, 2), (5, 5)]
result = []
for x, y in my_coords:
    if x**2 + y**2 <= 1:
        result.append((x, y))

Generating a circle

from math import sin, cos, radians
result = []
for i in range(360):
    x = cos(radians(i))
    y = -sin(radians(i))
    result.append((x, y))

Solution 3

If you know the size of the data in advance, use a numpy array.

import numpy
arr = numpy.array([ [x,y] for x,y in get_coords() ])

If you need to append data on-the-fly, use a list of tuples.

l = []
for x,y in get_coords():
    l.append((x,y))

Solution 4

A tuple is probably sufficient for simple tasks, however you could also create a Coordinate class for this purpose.

class Coordinate(object):
    def __init__(self, x, y):
        self.x = x
        self.y = y

    def __repr__(self):
        return 'Coordinate({0.x:d}, {0.y:d})'.format(self)

>>> coord = Coordinate(0, 0)
Coordinate(0, 0)
>>> coord.x = 1
>>> coord.y = 2
>>> coord
Coordinate(1, 2)
>>> coord.x
1
>>> coord.y
2

Notes

Python 2.5 compatibility

Use the following __repr__ method:

def __repr__(self):
    return 'Coordinate(%d, %d)'.format(self)

Floating point coordinates

Floating point coordinates will be stored as is, but the __repr__ method will round them. Simply replace :d with :.2f (the same for %), where 2 is the number of decimal points to display.

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