Adding a constant tuple value to a list of tuples

Question

Hi

I have a list of tuples (each tuple item is a pair of integers) and I would like to add a constant value to each tuple in the list.

For example [(x0,y0),(x1,y1),...] -> [(x0+xk,y0+yk),(x1+xk,y1+yk)....]

xk,yk are constants

How do I do this

Thanks

Answer 1

an example to add things to tuple

>>> a=(1,2)
>>> a+=(1,)
>>> a
(1, 2, 1)

you can adapt it to your requirement

Answer 2

Use numpy, e.g.,

>>> import numpy as np
>>> a = np.array([[1,2],[2,3]])
>>> print a
[[1 2]
 [2 3]]
>>> print a + 2
[[3 4]
 [4 5]]

Answer 3

>>>> l = [(1,2), (3,4)]
>>>> for i, e in enumerate(l):
....     l[i] = (e[0]+xk, e[1]+yk)

As always, untested. ;-)

If you don't need to do it in place, it's even simpler

>>>> l = [(e[0]+xk, e[1]+yk) for e in l]

Answer 4

You can't add a constant to a tuple because tuples are immutable.

You can however create a new tuple from the old one by incrementing it's values. See jae's answer for the basics of how to do this.

You should note however that you will be creating a lot of new tuples in this loop and this may not be a very efficient way of handling this. You should investigate numpy (as suggested by nikow) or perhaps using lists or coordinate objects instead of tuples.

Answer 5

Solution:

l = [(i[0]+k[0], i[1]+k[1]) for i in l]

Test code:

l = [(1,2), (3,4)]
k = (10, 100)
l = [(i[0]+k[0], i[1]+k[1]) for i in l]
assert l == [(11, 102), (13, 104)]