Legend - 1 year ago 171

Python Question

I am playing with python and am able to get the intersection of two lists:

`result = set(a).intersection(b)`

Now if

`d`

`a`

`b`

`c`

`d`

`d = [[1,2,3,4], [2,3,4], [3,4,5,6,7]]`

then the result should be

`[3,4]`

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Answer Source

for 2.4, you can just define an intersection function.

```
def intersect(*d):
sets = iter(map(set, d))
result = sets.next()
for s in sets:
result = result.intersection(s)
return result
```

for newer versions of python:

the intersection method takes an arbitrary amount of arguments

```
result = set(d[0]).intersection(*d[:1])
```

alternatively, you can intersect the first set with itself to avoid slicing the list and making a copy:

```
result = set(d[0]).intersection(*d)
```

I'm not really sure which would be more efficient and have a feeling that it would depend on the size of the `d[0]`

and the size of the list unless python has an inbuilt check for it like

```
if s1 is s2:
return s1
```

in the intersection method.

```
>>> d = [[1,2,3,4], [2,3,4], [3,4,5,6,7]]
>>> set(d[0]).intersection(*d)
set([3, 4])
>>> set(d[0]).intersection(*d[1:])
set([3, 4])
>>>
```

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