[sushi4664]

Lets assume that I have the following code:

Code:

shuffle($_SESSION['useNums']);//shuffles possible questions
$randNum=array_pop($_SESSION['useNums']);//selects from shuffled list

The array useNums has a total of 7000-10000 integers (they start from 0 and go to the number of elements the array contains)

How efficient is that method? I am really worried because I expect this website to get millions of hits after it is released. I do not want to overuse the processor and get my account banned from my hosting service (I am not on a dedicated server).

On the other hand, is there a more efficient method of selecting a number from a list randomly and maintaining the fact that the number selected will be removed from the array?

[Jay6390]

PHP Code:

$randnum = $_SESSION['useNums'][rand(0,count($_SESSION['useNums'])-1)]; 

Something like that?

[sushi4664]

Yea, I had that before, but remember that I don't want an integer to appear twice. Even though the probability is low, the randomly selected value could be selected again.

And I am still curious about the run time efficiency of the shuffle method.

[Jay6390]

PHP Code:

$x=rand(0,count($_SESSION['useNums'])-1);
$randnum = $_SESSION['useNums'][$x];
unset($_SESSION['useNums'][$x]; 

Like that then? I dont know the efficiency difference between them, but selecting a random number must really be more efficient that swapping round a huge array of numbers

[nova912]

sorry, misunderstood ---

[Jay6390]

What?

[sushi4664]

Originally Posted by nova912

sorry, misunderstood ---

Wait what did u misunderstand? Is it something that I need to clear up?

Originally Posted by Jay6390

PHP Code:

$x=rand(0,count($_SESSION['useNums'])-1);

$randnum = $_SESSION['useNums'][$x];

unset($_SESSION['useNums'][$x]; 

Like that then? I dont know the efficiency difference between them, but selecting a random number must really be more efficient that swapping round a huge array of numbers

Yea, I think I will go back to this method, it only makes sense that this would be faster. Though, if anyone has the run time analysis on these pieces of code, that would be really nice. Or even some clarification on how the shuffle method works and how processor consuming it is.

[job0107]

Originally Posted by sushi4664

Wait what did u misunderstand? Is it something that I need to clear up?



Yea, I think I will go back to this method, it only makes sense that this would be faster. Though, if anyone has the run time analysis on these pieces of code, that would be really nice. Or even some clarification on how the shuffle method works and how processor consuming it is.

It should be much faster because a shuffle is like a sort and sorting takes a lot of time, but the way it's written it won't work as expected. It's missing one line of code to make it work properly.

The way it's written, when a random number is picked it unsets that element.
So in the array that element will be missing.
Say for instance you have 4 elements then the count would be four.
A rand number of 2 comes up and the third element gets unset.
Now you have a count of 3.
So if a rand number of 2 comes up next the third element will not be there because it was unset.
So the remaining elements need to be merged so the indexing is correct.
Then it will work without any problems.

Like this:

PHP Code:

$rand_element=rand(0,count($_SESSION['useNums'])-1);
$randnum = $_SESSION['useNums'][$rand_element];
unset($_SESSION['useNums'][$rand_element]);
$_SESSION['useNums']=array_merge($_SESSION['useNums']); 

[UnrealEd]

you could also use the array_rand function instead of the rand function, that way you don't need to count the number of elements in the array first (php will probably do it for you in the array_rand function, so I don't think you'll see a lot of improvement there).

[sushi4664]

Originally Posted by job0107

It should be much faster because a shuffle is like a sort and sorting takes a lot of time, but the way it's written it won't work as expected. It's missing one line of code to make it work properly.

The way it's written, when a random number is picked it unsets that element.
So in the array that element will be missing.
Say for instance you have 4 elements then the count would be four.
A rand number of 2 comes up and the third element gets unset.
Now you have a count of 3.
So if a rand number of 2 comes up next the third element will not be there because it was unset.
So the remaining elements need to be merged so the indexing is correct.
Then it will work without any problems.

Like this:

PHP Code:

$rand_element=rand(0,count($_SESSION['useNums'])-1);
$randnum = $_SESSION['useNums'][$rand_element];
unset($_SESSION['useNums'][$rand_element]);
$_SESSION['useNums']=array_merge($_SESSION['useNums']); 

Ok, this is what I was looking for. I will stick with this method.

Originally Posted by UnrealEd

you could also use the array_rand function instead of the rand function, that way you don't need to count the number of elements in the array first (php will probably do it for you in the array_rand function, so I don't think you'll see a lot of improvement there).

And, nice thinking! I hadn't thought of that.

Thanks!