7

I'm quite familiar with a few methods of cards, primarily Riffling and Mongean* shuffling. The issue I have with those is that the Riffling shuffle tends to bend cards and wear them out, as well as not working well with a large deck. The Mongean method isn't particularly good at shuffling large decks either.

Unlike this thread I'm not dealing with a well organised deck, but I am dealing with a large deck (80 cards plus).

I've considered cutting the deck in two first, but that then takes twice as long.

What is the best method for shuffling in this case?

*Instead of moving one card at a time, I move a random number.

2

With the implied restriction on time combined with the explicit restriction to keep the cards pristine, I'd suggest using extra space to shuffle. Here's what I do with large decks of cards:

  1. Divide the large deck into several smaller piles. For 80 cards, I'd make about 8 piles of 7-15 cards
  2. Select two piles at random and combine them using a hindu shuffle (unlike in the video, when I do it, I do it by grasping the wider-side rather than the narrower side of the cards for better control of larger decks.
  3. After a few shuffles, grab another random pile and add it to the deck
  4. Continue until all decks have been added.
  5. Continue with several more Hindu shuffles until you're satisfied.

If you cannot keep all cards in your hand, recombine/shuffle half the cards, then recombine/shuffle the other half, put the two halves together (just stacking them) into 1 full deck again. Finally, repeat the entire process two or three times (this is only necessary if you had to do a simple stacking).

  • How long does this technique take normally? – Pureferret Dec 31 '11 at 15:19
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    I just did it last night for a stack of about 150 cards and it took about 90 seconds. – Neal Tibrewala Jan 1 '12 at 0:11
  • How well does it work? Any analysis/justification? – BartoszKP Dec 28 '16 at 14:09
3

For me, I would divide the deck into smaller parts that you can handle. Riffle shuffle (or any way you like) those and mix the small decks together, one group at a time.

-2

I would do similar to the accepted answer but deal out a different number of piles that never are a multiple of the number of cards. Deal out the entire deck randomly as well to each of these piles, then combine the piles randomly always putting the next pile on the bottom or always putting the next pile on top. For example:

a deck of 80 cards should have the deck divided up by an odd number of stacks. We want the highest number we can take before it's too cumbersome. So say 7 stacks. 7 goes into 80 11 times with 3 left over. If you chose 9 stacks to deal out to then it would be 8 cards a stack with 8 left over. The numbers look more "messy" with the stack of 7 so let's go with it. Now you deal out randomly to each stack even keeping the piles uneven from the 11 increasing the imbalances of each stack. This adds even more randomness into the spread of the cards. Now you take each pile and combine them putting each stack on the bottom. There is no need to alternate top or bottom since you are choosing to pile the stacks randomly. Random is random, so it's faster to just keep it the same in one way but randomize it in your choice of what goes on the bottom.

The deck is now immediately shuffled. There is no reason to do any other type of shuffle. All the cards have been spaced out from each other by at least 7 spaces from their original position and with your randomness you increase or decrease that spacing randomly throughout. Then you stacked the spacing randomly again which gives 3 levels of randomization to the shuffle: the 7 spacing, the random up/down of spacing and the random piling. The faster you deal out the cards to the stacks, the faster this will finish but you will always have a complete shuffle with no need to do any other type of shuffle. Cutting the deck after is totally acceptable and encouraged.

EDIT: It takes me 30s to shuffle a 52 card deck in this way. Shuffling with 14 stacks, only added 15s to the time. The more stacks the better but this will undoubtedly shuffle the deck without damaging the cards.

  • Welcome to B&CG! – Pat Ludwig Dec 30 '18 at 18:40
  • If you have a means of truly randomly assigning a pile for each card, it is more efficient (both in time and in handling) and more effective (in randomising card order) to just use it in making the full deck. This method is not justified and even points out that it is not a true shuffle with all permutations possible. – Nij Dec 30 '18 at 20:31
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    Please use the Contact Us form to have your accounts merged, so that you can edit your post without restrictions. – Glorfindel Dec 31 '18 at 8:06

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