unique across multiple cells or arrays

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Alexander Winter
Alexander Winter 2020-8-6
编辑： Stephen23 2020-8-8
Let's say I got a bunch of arrays in a cell array that are not the same size:
a = {[1 2 2], [2 3 6 3], [4 3 5 6 7]}
I want to remove all dupplicates accross the cells. I want to remove things in a cell that are in the other cells as well as the dupplicates in each cells:
Example output:
b = {[1 2], [3 6], [4 5 7]}
I would like to have this vectorized. I can simply loop but this is very slow:
others = [];
for i = 1:length(a)
b{i} = setdiff(unique(a{i}), others);
others = [others, b{i}];
end
I'm thinking of putting it all into a single array to call unique:
b = unique([a{:}])
% now b = [1 2 3 4 5 6 7]
But I don't think there's anyway to put it back into its respective cells since the order is lost and I don't know where the limits are
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per isakson
per isakson 2020-8-8
Thanks for sharing. I cannot think of anything simpler.
Matt J
Matt J 2020-8-8
The process you describe does not have a well defined output. For the example you gave,
a = {[1 2 2], [2 3 6 3], [4 3 5 6 7]}
this would also satisfy the requirements:
b = {[1], [2 3], [4 5 6 7]}

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Stephen23
Stephen23 2020-8-8
编辑：Stephen23 2020-8-8
>> a = {[1,2,2],[2,3,6,3],[4,3,5,6,7]};
>> [u,x] = unique([a{:}],'first'); % or 'last' to allocate to the last cell where value occurs.
>> [~,y] = sort(x);
>> n = cumsum([1,cellfun(@numel,a)]);
>> z = sum(bsxfun(@ge,x(y),n),2);
>> c = accumarray(z,u(y),[],@(m){m});
>> c{:}
ans =
1
2
ans =
3
6
ans =
4
5
7
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Stephen23
Stephen23 2020-8-8
编辑：Stephen23 2020-8-8
@the cyclist: well spotted!
The behavior you describe is caused by the presence/lack of indexing into that cell: if accumarray is not told to put anything in that cell, then that cell simply won't be created. That occurs for any number of trailing cells which only contain duplicates of prior numbers, not just the last cell.
It can be resolved quite easily by telling accumarray the required output array size:
c = accumarray(z,u(y),size(a),@(m){m});
% ^^^^^^^ output size
Alexander Winter
Alexander Winter 2020-8-8
编辑：Alexander Winter 2020-8-8
In my case the empty array is not desirable (I'm discarding them afterwards) so your initial solution is better for me. Thanks!

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