So I got a list in python like this:
[1,2,3,4]
And I want the combinations between the number 3 with every number something like this:
[(1,3),(2,3),(3,4)]
Is there something I can use? I know there is something called itertools, but I'm kinda new so i'm not sure how to use it.
Thank you!
You might want to use a list comprehension:
orig_list = [1,2,3,4]
[(entry, 3) for entry in orig_list if entry != 3] # [(1, 3), (2, 3), (4, 3)]
If you're not interested in duplicate values you can make it into a set:
orig_list = set([1,2,3,4])
[(entry, 3) for entry in orig_list if entry != 3] # [(1, 3), (2, 3), (4, 3)]
_ as a variable if you do not want to use that variable
An easy way to do this is using a loop:
list2 = []
for x in list1:
list2.append((x,3))
print(list2)
If you want to get rid of (3,3) use:
list2 = []
for x in list1:
if x != 3:
list2.append((x,3))
print(list2)
you could use list comprehension with itertools.combinations:
import itertools
[e for e in itertools.combinations([1,2,3,4], 2) if 3 in e]
output:
[(1, 3), (2, 3), (3, 4)]
even better you could use itertools.repeat:
from itertools import repeat
l = [1,2,3,4]
[(f, s) for f, s in zip(l, repeat(3)) if f != 3]
output:
[(1, 3), (2, 3), (4, 3)]
O(n) problem into a O(n²) problem (n choose 2 is n * (n - 1) / 2 work); for every value you generate, you have to filter out ~n. Fine if the input is length 4, less so if it's length 1000.You could use:
l = [1,2,3,4]
[(l[i], 3) for i in range(l.index(3))] + [(3, l[i]) for i in range(l.index(3)+1, len(l))]
which gives the output:
[(1, 3), (2, 3), (3, 4)]
itertoolsfor this.[(1, 2), (1, 3), (1, 4), (2, 3), (2, 4), (3, 4)]?