Matlab Create an array with element of a for loop

Question

Here's my code:

N = 1:999;

for i = N
    if rem(i,3) == 0 || rem(i,5) == 0
        v(i,1) = i
    end      
end

Te problem is that I get an Array with some zeros in, but I just want an an arraywith the values comforming to my conditions.

How can I fix it?

Thank you!

I don't understand your question. What is the output you are expecting? — Daniel
– Daniel, Commented Jun 16, 2014 at 18:38
N=1:999; then v=(rem(N,3)==0)|(rem(N,5)==0);. Is that what you want? Or are you wanting: v= N( (rem(N,3)==0) | (rem(N,5)==0) ); — brechmos
– brechmos, Commented Jun 16, 2014 at 18:40

brechmos · Accepted Answer · 2014-06-16 18:46:25Z

2

I think the OP is looking for a result like:

v= N( (rem(N,3)==0) | (rem(N,5)==0) );

though without looping... :-)

answered Jun 16, 2014 at 18:46

brechmos

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6 Comments

Justin Fletcher Over a year ago

In case you're curious, your answer is 72x faster than mine. : )

brechmos Over a year ago

!! :-). Obviously there might be a reason the OP needs loops, but I love to look for ways to NOT use them. You (@Fletch) are right to leave your loop there in case that is what the OP wants but it is always fun to think of ways to create a solution without loops.

Justin Fletcher Over a year ago

Are you on the Code Review SE site? You should check it out, lots of stuff like this on there.

brechmos Over a year ago

@Fletch... no, haven't been. Will be now. Thanks! Years ago (many, many years ago) Mathworks had contests (maybe still do) to produce the most efficient/compact code. It was a lot of fun.

brechmos Over a year ago

@Fletch, on that note, I learned Python years ago by doing the projecteuler.net problems. Lots of fun. (Unfortunately, Project Euler is now offline).

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Justin Fletcher · Accepted Answer · 2014-06-16 19:09:23Z

0

I'm assuming that you're using a loop for a reason, and am not removing it from my solution. However, loops should be avoided where possible.

If I understand your question, you're trying to store only those values of i which correspond to a true conditional evaluation. You're problem is that you're using i as your index value inside the assignment statement. Use the end index keyword. Like so:

N = 1:999;
v = [];

for i = N
    if rem(i,3) == 0 || rem(i,5) == 0
        v(end+1) = i
    end      
end

edited Jun 16, 2014 at 19:09

answered Jun 16, 2014 at 18:45

Justin Fletcher

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