I want to swap every occurrence of two elements in a list of lists. I have seen previous answers but they are different from what I'm trying to do. Also, I am looking for a clean and concise way (preferably list-comprehension) for this purpose.
Input
my_list = [[1,2], [1,3], [1,4], [3,2]]
Output
my_list = [[2,1], [2,3], [2,4], [3,1]]
I am trying to do something like this but no success:
[1 if i==2 else i, 2 if i==1 else i for i in my_list]
Here's a simple solution using list comprehension:
my_list = [[1,2], [1,3], [1,4], [3,2]]
a = 1
b = 2
my_list = [[a if i==b else b if i==a else i for i in j] for j in my_list]
print(my_list) # [[2, 1], [2, 3], [2, 4], [3, 1]]
If you want to add more elements to replace you can use a dictionary:
swap = {
1: 2,
2: 1
}
my_list = [[swap.get(i, i) for i in j] for j in my_list]
Someone else will probably answer with something better, but this would work.
def check(num):
if num == 1:
return 2
elif num == 2:
return 1
else:
return num
out = [[check(j) for j in i] for i in my_list]
If you need to swap 1's with 2's, this one-liner will work:
>>> my_list = [[1,2], [1,3], [1,4], [3,2]]
>>> print([[(lambda k: (1 if val == 2 else 2) if val in [1, 2] else val)(val) for val in sub_list] for sub_list in my_list])
[[2, 1], [2, 3], [2, 4], [3, 1]]
read the second line from right to left... in chunks!
[[2,1], [2,3], [2,4], [3,1]]as opposed to[[2, 1], [3, 1], [4, 1], [2, 3]]?