Programming Forums > Application Development > Software Design and Algorithms

scm007 · Feb 20th, 2007, 2:53 PM

Here is the deal, I have an array, say array1 that I want to take a random seed of. How do I do this? Basically I want to take a random sampling of array1 and make a new array, called list that is built from these values, with no duplicates. A 3rd array would also be made, called outlist, which would be all the values in array1 that are not in list.

Thanks!

DaWei · Feb 20th, 2007, 2:59 PM

Isn't this a cross-post? Tsk, tsk. Please read the forum's rules.

Your terminology is not correct. A seed is a value that you use when initializing a random-number generator. If you want to select an array element randomly, generate a random number in the range of the number of elements that the array contains. If you don't want duplicates, you'll have to check for that. If you want to divvy up the contents, you'll have to write that. To avoid duplicates, you could also make a sequential list of numbers from 0 to the length of the array (there would then be no duplicates) and shuffle (randomize) it, then use it for the selection. This would prevent duplicate elements but NOT duplicate values. You'll just have to check for that.

scm007 · Feb 23rd, 2007, 2:48 PM

I purposefully avoided cross posting because the other post was looking for ADA code, but since it received no responses I thought I would go a step up.

Thanks for the tip! But... how would I shuffle a range of numbers randomly? Where can I find a shuffle algorithm?

Arevos · Feb 23rd, 2007, 3:45 PM

There was a post on this a while back, IIRC. One of the easiest shuffle algorithms is:

(Toggle Plain Text)

for i = 0 to (array.length - 1)
    r = random number from 0 to array.length - 1
    swap values of array[i] and array[r]

titaniumdecoy · Feb 23rd, 2007, 4:26 PM

If you want to avoid duplicate values, copy each unique value from the original list into a new list, say outlist. Then shuffle outlist and remove each element you add to list.

kruptof · Feb 24th, 2007, 3:51 AM

or you could shuffle the array by using some sort of key then swapping the values

(Toggle Plain Text)

	for(int i=0;i<15;i++)
	{
		j = arr[i]+key.at(j % strlen(key.c_str()));
		j = j % 15;
		swap(arr[i],arr[j]);
	}

Feb 20th, 2007, 2:53 PM	#1
scm007 Newbie Join Date: Jan 2006 Posts: 27 Rep Power: 0	Random Seed of an array-- pseudocode? Here is the deal, I have an array, say array1 that I want to take a random seed of. How do I do this? Basically I want to take a random sampling of array1 and make a new array, called list that is built from these values, with no duplicates. A 3rd array would also be made, called outlist, which would be all the values in array1 that are not in list. Thanks!

Feb 20th, 2007, 2:59 PM	#2
DaWei Resident Grouch Join Date: Jun 2005 Posts: 6,453 Rep Power: 10	Isn't this a cross-post? Tsk, tsk. Please read the forum's rules. Your terminology is not correct. A seed is a value that you use when initializing a random-number generator. If you want to select an array element randomly, generate a random number in the range of the number of elements that the array contains. If you don't want duplicates, you'll have to check for that. If you want to divvy up the contents, you'll have to write that. To avoid duplicates, you could also make a sequential list of numbers from 0 to the length of the array (there would then be no duplicates) and shuffle (randomize) it, then use it for the selection. This would prevent duplicate elements but NOT duplicate values. You'll just have to check for that. __________________ Abstraction doesn't make it impossible to write bad code; it makes it possible to write superior code. Contributor's Corner: Grumpy on C++ Exceptions DaWei on Pointers

Feb 23rd, 2007, 3:45 PM	#4
Arevos Programming Guru Join Date: Aug 2005 Location: England Posts: 1,499 Rep Power: 5	There was a post on this a while back, IIRC. One of the easiest shuffle algorithms is: (Toggle Plain Text) for i = 0 to (array.length - 1) r = random number from 0 to array.length - 1 swap values of array[i] and array[r] for i = 0 to (array.length - 1) r = random number from 0 to array.length - 1 swap values of array[i] and array[r]

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
ADA Random Seed of an Array	scm007	Other Programming Languages	1	Mar 25th, 2007 9:05 PM
relation between array and pointer	n00b	C++	6	Oct 12th, 2006 3:38 PM
Median/Mode in arrays? {Need help}	Java\|Tera	Java	27	Nov 29th, 2005 10:50 AM
random numbers in 2D array	cwl157	Java	4	Apr 29th, 2005 6:08 AM
Installing IPB 2.03	bh4575	Other Web Development Languages	0	Apr 23rd, 2005 2:36 AM

Feb 23rd, 2007, 2:48 PM	#3
scm007 Newbie Join Date: Jan 2006 Posts: 27 Rep Power: 0	I purposefully avoided cross posting because the other post was looking for ADA code, but since it received no responses I thought I would go a step up. Thanks for the tip! But... how would I shuffle a range of numbers randomly? Where can I find a shuffle algorithm?

Feb 23rd, 2007, 4:26 PM	#5
titaniumdecoy Expert Programmer Join Date: Nov 2005 Posts: 843 Rep Power: 3	If you want to avoid duplicate values, copy each unique value from the original list into a new list, say outlist. Then shuffle outlist and remove each element you add to list.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Programming Forums > Application Development > Software Design and Algorithms

Random Seed of an array-- pseudocode?