# Creating a random combination

by reldridge
Tags: combination, creating, random
 P: 5 I am creating a random combination(code) for a client. I need to see what the total number of combinations there can be. Please let me know if I am using the wrong word Combination vs Permutations. Formula: 2 letters + 2 numbers + 2 letters example: TR12FR The random letters are taken from 24 values: ABCDEFGHJKLMNPQRSTUVWXYZ The random Numbers are taken from 8 Values: 23456789 Any help would be greatly appreciated. Thanks Ryan.
 P: 3,101 combination is right you're selecting letters, numbers and more letters: Choices for each character of your 6 charcter code: 24 * 24 * 8 * 8 * 24 * 24 = total number of codes possible Now if these could be rearranged then you'd have to worry about permutations to elimnate repeats in your counts.
 P: 5 Thank you - So de-duping these down to create 2.5 million unique codes using this formula will not be an issue, sense there are 21,233,664 possibilities.
 P: 3,101 Creating a random combination okay what do you mean by de-duping?
 P: 5 Well sense this is just a random generator out of excel the possibility of it creating a duplicate is there, so i will need to just remove dupes, or nth select down to 2.5 million unique codes. Just needed to make sure that the 6 digit using that formula could create that many unique codes.
PF Gold
P: 6,514
 Quote by reldridge Well sense this is just a random generator out of excel the possibility of it creating a duplicate is there ...
So you have a belief that "true" random would not include any dupes?

How would you create 100000 consecutive random numbers from 1 to 100 ?
 P: 3,101 this reminds of how new programmers used to construct a deck of randomly sorted cards. generate a number from 0-51 check if its present in the crd deck array if so then generate another. The better approach is to generate a sorted sequence of cards into an array and then to randomly shuffle two cards by selecting two indexes at random and swapping the cards.
P: 5
 Quote by phinds So you have a belief that "true" random would not include any dupes?
No belief, was just stating that there could be duplicate codes during the random selection and i would need to remove the duplicates until reaching my goal of 2.5 unique codes...
 P: 5 Thanks for the help.

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