How do I avoid creating intermediate variables?

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Say I have a vector of data x and a function f(x).
Now say I want to evaluate f(x) only for x>2, so I do:
ind=x>2; y=f(x(ind));
Now say I want to find y>5;
ind2=y>5;
Now how can I use this information to get the x values corresponding to the y>5 values, WITHOUT using this crude method where I create an intermediate variable:
x_intermediate = x(ind1); % I want to avoid creating this
x_answer = x_intermediate(ind2);

Accepted Answer

Walter Roberson
Walter Roberson on 30 May 2011
ind1 = find(x>2);
y = f(x(ind1));
x(ind1(y>5))

More Answers (2)

Matt Fig
Matt Fig on 30 May 2011
Is your complaint about the extra typing, or the extra variable in the workspace? If the latter, then one way to avoid this kind of thing in general is:
x_answer = x(ind1); % This will be overwritten.
x_answer = x_answer(ind2);
This strategy will serve you beyond this specific problem.

Andrei Bobrov
Andrei Bobrov on 30 May 2011
xy = [x f(x)];
out = xy(xy(:,1)>2&xy(:,2)>5,:)
  1 Comment
AJP
AJP on 30 May 2011
Perhaps I should clarify that the x vector is very large. I therefore want to avoid the creation of any extra variables because they essentially just repeat data already stored in x.
Essentially what I want to do is to use the information in ind1 and ind2 to "filter" the x values so I can pass these filtered values to another, later function.

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