set-intersection

I have a collection of std::set . I want to find the intersection of all the sets in this collection, in the fastest manner. The number of sets in the collection is typically very small (~5-10), and the number of elements in each set is is usually less than 1000, but can occasionally go upto around 10000. But I need to do these intersections tens of thousands of time, as fast as possible. I tried to benchmark a few methods as follows: In-place intersection in a std::set object which initially copies the first set. Then for subsequent sets, it iterates over all element of itself and the ith set

Currently, I think my best option is to use std::set_intersection, and then check if the size of the smaller input is the same as the number of elements filled by set_intersection. Is there a better solution? Klark Try this: if (std::includes(set_one.begin(), set_one.end(), set_two.begin(), set_two.end())) { // ... } About includes() . The includes() algorithm compares two sorted sequences and returns true if every element in the range [start2, finish2) is contained in the range [start1, finish1). It returns false otherwise. includes() assumes that the sequences are sorted using operator<(),

If I have a variable number of sets (let's call the number n ), which have at most m elements each, what's the most efficient way to calculate the pairwise intersections for all pairs of sets? Note that this is different from the intersection of all n sets. For example, if I have the following sets: A={"a","b","c"} B={"c","d","e"} C={"a","c","e"} I want to be able to find: intersect_AB={"c"} intersect_BC={"c", "e"} intersect_AC={"a", "c"} Another acceptable format (if it makes things easier) would be a map of items in a given set to the sets that contain that same item. For example:

I have a query, consider the following example as a intermediate data after performing some aggregation on a sample dataset; fileid field contains the id of a file, and the user array containing array of users, who made some changes to the respective file { “_id” : { “fileid” : 12 }, “_user” : [ “a”,”b”,”c”,”d” ] } { “_id” : { “fileid” : 13 }, “_user” : [ “f”,”e”,”a”,”b” ] } { “_id” : { “fileid” : 14 }, “_user” : [ “g”,”h”,”m”,”n” ] } { “_id” : { “fileid” : 15 }, “_user” : [ “o”,”r”,”s”,”v” ] } { “_id” : { “fileid” : 16 }, “_user” : [ “x”,”y”,”z”,”a” ] } { “_id” : { “fileid” : 17 }, “_user” :

I'm new to programming and I've recently come across an issue with finding the intersection of n vectors, (int vectors) that have sorted ints. The approach that I came up with has a complexity of O(n^2) and I am using the std::set_intersect function. The approach that I came up with is by having two vectors: the first vector would correspond to the first vector that I have, and the second would be the second vector. I call set intersection on the two and overwrite to the first vector, then use the vector clear function on the second. I then overwrite the next vector to the second, and repeat

This is somewhat related to a question I asked not too long ago today. I am taking the intersection of two lists as follows: inter = set(NNSRCfile['datetimenew']).intersection(catdate) The two components that I am taking the intersection of belong to two lengthy lists. Is it possible to get the indices of the intersected values? (The indices of the original lists that is). I'm not quite sure where to start with this one. Any help is greatly appreciated! I would create a dictionary to hold the original indices: ind_dict = dict((k,i) for i,k in enumerate(NNSRCfile['datetimenew'])) Now, build