Problem 801. Construct an index vector from two input vectors in vectorized fashion

Created by Christopher

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Create an index vector defined by two input vectors, one defining the beginnings of one or more index ranges, and the other defining the ends of the ranges.
The difficult part is that for and while loops are disallowed. No looping! [I apologize for the rudimentary regexp test for 'for' 'while' and 'eval'.] My test cases scan for usage of these substrings, so choice of variable names is effectively restricted as well.
So given 2 input vectors x1 and x2, the desired output is a third vector y, containing [x1(1):x2(1) x1(2):x2(2) ... x1(end):x2(end)]
Example:
 x1 = [1 5 12];
 x2 = [2 8 21];
Result:
 y = [1 2 5 6 7 8 12 13 14 15 16 17 18 19 20 21]

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Last Solution submitted on Dec 15, 2024

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Dirk Engel on 27 Jun 2012

Please do not check for the occurance of "for" in general, because "UniFORmOutput" has nothing to do with looping ;-)

Freddy on 27 Jun 2012

Your predefined function signature has only one parameter, altough two were submitted. Same problem without the "for" restriction: http://www.mathworks.com/matlabcentral/cody/problems/555-low-high-low-high-turn-around-create-a-subindices-vector

Pascal Wenger on 28 Feb 2017

This is an excellent problem.

Allen on 13 Oct 2017

I agree with Dirk. Change your regexp to check for instances of eval, for, and while that are not preceded or followed by additional letters.

Payam Morsali on 17 Nov 2019

give me a hint, should we use a specific function here?

Rafael S.T. Vieira on 23 Jul 2020

Tip: replace UniformOutput with uni.

Rik on 25 Feb 2021

Actually arrayfun should also be outlawed, as that simply hides the loop at a performance cost. I haven't seen a vectorized solution yet, only recursions and implicit loops (and the usual cheat-submissions).

If you want a more robust cheat-detection you should have a separate test which runs as first test. That one should not call the submission to avoid it overwriting functions like fileread and assert.

Brandon on 23 Mar 2023

I hate problems that disallow basic programming skills. Unless you know the one specific function that probably just does this for free, you have no idea how to solve it. And from the sounds of it, there isn't a vectorized solution anyway.

I wish you could peek at the functions in the solutions to see what people used.

Dyuman Joshi on 24 Mar 2023

Rik, your suggestion for a separate test case for cheat detection has been implemented. And ideally, arrayfun should be banned as well for the reason you have stated, but since author has not chosen to, I will refrain from doing so as well.

Also, I can say that the reference solution is a vectorized solution.

Brandon, the idea of such problems is to allow you to brainstorm through different methods, approaches and concepts, and in doing so, learn new programming techniques and/or functions. Without the restrictions, the problem would be extremely easy. And there are already problems with the same theme without any restrictions on Cody, you can explore and find them easily.

As I stated above, I can assure your there is atleast one vectorized solution.

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Problem 801. Construct an index vector from two input vectors in vectorized fashion

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Problem 801. Construct an index vector from two input vectors in vectorized fashion

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