I am trying to obtain a series of vectors made of elements from a larger vector given they exceed a threshold

I have Z=[6 7 8 5 6 7 8 3 2 4]' vector

for i=1:10; A(i) =Z(Z>Z(i)); end

For some reason its not working

Answer 1

[Matthew Eicholtz]

The reason your code does not currently work is because you are trying to assign a vector ( Z(Z>Z(i)) ) to a scalar element in a numeric array ( A(i) ). Since the size of your vector may vary on each iteration, I suggest using a cell array.

To do this, just change A(i) to A{i}.

[Mark Smith]

I tried your method and although no error is given, when in the command window I input for example A(3) I still do not get a vector of elements that I need.

[Matthew Eicholtz]

Does A{3} work instead of A(3)?

[Matthew Eicholtz]

An alternative approach if you do not want to use a cell array is to create a logical mask as follows:

Z = [6 7 8 5 6 7 8 3 2 4]';
mask = bsxfun(@gt,Z,Z');

Then, if you want to get the elements that are greater than the 4th element, for example, use:

Z(mask(:,4))

Answer 2

[Roger Stafford]

It's not clear whether you want those Z elements which exceed some fixed value or those which make up a monotone increasing sequence.

For a fixed value L:

A = Z(Z>L);

For selecting only those Z which constitute a monotone increasing sequence:

t(1) = true;
for k = 2:length(Z)
  t(k) = (max(Z(1:k-1))<Z(k));
end
A = Z(t);