Intersection of multiple arrays without for loop in MATLAB

问题

I've always been told that almost all for loops can be omitted in MATLAB and that they in general slow down the process. So is there a way to do so here?:

I have a cell-array (tsCell). tsCell stores time-arrays with varying length. I want to find an intersecting time-array for all time-arrays (InterSection):

InterSection = tsCell{1}.time
for i = 2:length{tsCell};
    InterSection = intersect(InterSection,tsCell{i}.time);
end

回答1:

Here's a vectorized approach using unique and accumarray, assuming there are no duplicates within each cell of the input cell array -

[~,~,idx] = unique([tsCell_time{:}],'stable')
out = tsCell_time{1}(accumarray(idx,1) == length(tsCell_time))

Sample run -

>> tsCell_time = {[1 6 4 5],[4 7 1],[1 4 3],[4 3 1 7]};

>> InterSection = tsCell_time{1};
for i = 2:length(tsCell_time)
    InterSection = intersect(InterSection,tsCell_time{i});
end
>> InterSection
InterSection =
     1     4

>> [~,~,idx] = unique([tsCell_time{:}],'stable');
out = tsCell_time{1}(accumarray(idx,1) == length(tsCell_time));
>> out
out =
     1     4

回答2:

Here's another way. This also assumes there are no duplicates within each original vector.

tsCell_time = {[1 6 4 5] [4 7 1] [1 4 3] [4 3 1 7]}; %// example data (from Divakar)
t = [tsCell_time{:}]; %// concat into a single vector
u = unique(t); %// get unique elements
ind = sum(bsxfun(@eq, t(:), u), 1)==numel(tsCell_time); %// indices of unique elements
    %// that appear maximum number of times
result = u(ind); %// output those elements

来源：https://stackoverflow.com/questions/35825435/intersection-of-multiple-arrays-without-for-loop-in-matlab

标签

arrays

matlab

cell

vectorization

intersection