多个集合的交集迭代

Question

I have a dataframe (but it also can be just sets/lists):

Group    Letter      
  1    {a,b,c,d,e}
  2    {b,c,d,e,f}
  3    {b,c,d,f,g}
  4    {a,b,c,f,g}
  5    {a,c,d,e,h}

I want to add column with intersection of group 1-2, 1-2-3, 1-2-3-4, 1-2-3-4-5. So it'll be sth like this:

Group    Letter      Intersection 
  1    {a,b,c,d,e}       None
  2    {b,c,d,e,f}     {b,c,d,e}
  3    {b,c,d,f,g}      {b,c,d}
  4    {a,b,c,f,g}       {b,c}
  5    {a,c,d,e,h}        {c}

I've read abt np.intersect1d, set.intersection, so I can do an intersection of multiple sets. But I don't know how to do it in smart way. Can someone help me with this problem?

Answer 1

You might itertools.accumulate for this task as follows

import itertools
letters = [{"a","b","c","d","e"},{"b","c","d","e","f"},{"b","c","d","f","g"},{"a","b","c","f","g"},{"a","c","d","e","h"}]
intersections = list(itertools.accumulate(letters, set.intersection))
print(intersections)

output

[{'e', 'a', 'b', 'c', 'd'}, {'b', 'e', 'c', 'd'}, {'b', 'c', 'd'}, {'b', 'c'}, {'c'}]

Note first element is {'e', 'a', 'b', 'c', 'd'} rather than None , so you would need to alter intersections in that regard.