How to find subset of a set without knowing the subset or parent set values

Question

I have two sets:

a = {x,x,x,x}
b = {x,x,x,x,x}

with x meaning unknown values

The exact arrangements or length or values of each set (a or b) are not fixed until they've been discovered. I am not able to know what exact values or which would be a subset of which but I need to be able to detect and perform some action once either is a subset of the other.

I understand I could do this using:

if a <= b or b <= a:

But the issue is that below this if statement, I must be sure of which one is a subset of the other because I perform some functions with the subset and the set such as filtering out the subset from the set. There's no room for maybes, like an if statement. And I do not want to write duplicate code.

How do you suggest I go about this?

Sources I have checked: Finding all the subsets of a set Finding subset of a set

If you've established that `a <= b or b <= a`, then `min(a, b, key=len)` will return whichever of the sets is smaller. — slothrop, Aug 13 '23 at 17:52
@slothrop does this work for list types also? That is if a and b are list — Alexander, Aug 13 '23 at 17:56
`a <= b` doesn't work for lists. You'd need to do `set(a) <= set(b)` etc to check whether the contents of one list are a subset of the other. — slothrop, Aug 13 '23 at 17:59
*"filtering out the subset from the set"* - Do you mean modify the existing set object or create a new one with the filtered result? — Kelly Bundy, Aug 13 '23 at 18:00
Can't you just do `a ^ b` for that then, without knowing which one is the subset? Do you need to know for the other "some functions"? — Kelly Bundy, Aug 13 '23 at 18:15
If you need to know which is the subset, then use an if/else. `if a < b: ... elif b < a: ...` — John Gordon, Aug 13 '23 at 18:35
See its [doc](https://docs.python.org/3/library/stdtypes.html#frozenset.symmetric_difference). — Kelly Bundy, Aug 13 '23 at 19:14
@JohnGordon I said no duplicate code. The actions I perform on both cases `if a < b: ... elif b < a: ...` are the same. — Alexander, Aug 13 '23 at 20:10
@KellyBundy The question title specifically says "subset". I assume equal sets are not subsets. — John Gordon, Aug 14 '23 at 00:34
The `if a < b` block does not need much code; simply assign two variables `superset = b` and `subset = a`, and the reverse for `elif b < a`. Then in the real processing section, operate on those variables instead of `a` and `b` directly. — John Gordon, Aug 14 '23 at 00:36
@JohnGordon Equal sets are subsets of each other. Or in other words, a set is a subset of itself. You're thinking of *proper* subsets, which they didn't say. — Kelly Bundy, Aug 14 '23 at 01:26
What does *"There's no room for maybes, like an if statement"* mean? — Kelly Bundy, Aug 14 '23 at 01:46

score 0 · Accepted Answer · answered Aug 15 '23 at 12:43

0

Thanks to @slothrop. This works! No matter the values of any of the list or set.

smaller_set = list(min(set(a), set(b), key=len))
larger_set = list(max(set(a), set(b), key=len))
print(smaller_set,'smaller_set')
print(larger_set,'larger_set')

answered Aug 15 '23 at 12:43

Alexander

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To avoid calling `min` and `max` which feels redundant as there are only two values, you can also go with something like `smaller, larger = (a, b) if len(set(a)) < len(set(b)) else (b, a)` (credit https://stackoverflow.com/a/3674252/6045800) – Tomerikoo Aug 15 '23 at 12:51

How to find subset of a set without knowing the subset or parent set values

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