When to use find over logical indexing

Question

I need to return the first value in an array that is greater than another particular value. I have:

find(A > val, 1, 'first')

According to this post: https://stackoverflow.com/a/9464886/1985603 find is unavoidable in this case. But, what about:

B = A(A > val);
B(1)

Is there a good reason to use one over the other here, other than the extra line?

Answer 1

Yes there is; speed! Especially for large arrays, find will be significantly faster.

Think about it: the operation A > val is the same in both cases, but

B = A(A > val)

extracts values from A, and copies them into a new array B, which will have to be allocated and copy-assigned, and the A(A> val) temporary will have to be destroyed.

All find(A>val, 1, 'first') does is walk the list of logicals, and return a single number when it encounters the first true value; this is a lot less useless copying/assigning/etc., and therefore, much faster.

As a rule of thumb, when you don't use the additional options in find, logical indexing is almost always preferable. When you need or use find's additional functionalities, the find option is almost always preferable.