CODEWITHSUNDEEP
arraysmatlabfor-loopmatrix
hazem
hazem

Reputation: 11

construct a matrix by removing different elements from an array without loops in matlab

Given a vector X of discrete positive integers with size 160*1, and a table Tb1 in size 40*200, that contains a list of indices to be deleted from X Each column from the 200 columns in Tb1 points to 40 elements to be deleted from original X.

I create a new matrix of the remaining 120*200 elements by using a for loop with 200 iterations, that at round i deletes 40 elements from a copy of the original X according to the indices listed in Tb1(:,i), but it takes too much time and memory.

How can I get the result without using loops and with a minimum number of operations?

Upvotes: 1

Views: 61

Answers (1)

rahnema1
rahnema1

Reputation: 15837

Here are different methods:

Method1:

idx = ~hist(tbl, 1:160);
[f,~]=find(idx);
result1 = reshape(M(f),120,200);

Method2:

idx = ~hist(tbl, 1:160);
M2=repmat(M,200,1);
result2 = reshape(M2(idx),120,200);

Method 3 & 4:

% idx can be generated using accumarray
idx = ~accumarray([tbl(:) reshape(repmat(1:200,40,1),[],1)],true,[160,200],@any);
%... use method 1 and 2

Method5:

M5=repmat(M,200,1);
M5(bsxfun(@plus,tbl,0:160:160*199))=[];
result5 = reshape(M5,120,200);

Assuming that M is an array of integers and tbl is the table of indices.

It can be tested with the following data:

M = rand(160,1);
[~,tbl] = sort(rand(160,200));
tbl = tbl(1:40,:);

However it is more efficient if you generate indices of elements to be remained instead of indices of elements to be removed.

Upvotes: 1

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