How do I avoid creating intermediate variables?

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AJP 2011-5-30

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https://ww2.mathworks.cn/matlabcentral/answers/8459-how-do-i-avoid-creating-intermediate-variables

采纳的回答： Walter Roberson

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);

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Answer 1

Walter Roberson 2011-5-30

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ind1 = find(x>2);
y = f(x(ind1));
x(ind1(y>5))

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AJP 2011-5-30

Brilliant, thanks Walter.

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Answer 2

Matt Fig 2011-5-30

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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.

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Answer 3

Andrei Bobrov 2011-5-30

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xy = [x f(x)];
out = xy(xy(:,1)>2&xy(:,2)>5,:)

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AJP 2011-5-30

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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