so… I was playing cards the other day with some friends…
I got rather irritated that when counting for point cards, he grouped all of them together for easier counting. I was always taught from my game playing family that you fan the cards out to count them so as to not group them together as that will cause them to be grouped together
What’s the Straight Dope? Does it really matter if they’re shuffled 7 or more times? (supposedly the number that distributes the cards in the ultimate randomness)
What kind of shuffle are you atlking about? The riffle, whichi s probably the most common? I actually have a friend who is a magician specializing in card tricks. He can do what they call a perfect shuffle. First of all he can divide the deck perfectly in half at will (seemingly) and then he shuffles the deck. And then when he does it again the deck is back to it’s originnal state. So although the deck has beeen shuffled twice, it is not shuffled at all.
The average person it probably does not matter a whole heckuva a lot. But to be safe the best shuffle is simple to mess the cards up in a big pile in front of everyone on the table. This is the way casinos do it at the poker tables if there isn’t an automatic shuffler.
What Gangster Octopus said. Also, the riffle shuffle is pretty ineffective unless you do it 7 or more times, and its weakness is that it tends to leave cards grouped together. People almost never shuffle the cards 7 times. Try it, it takes a long time. People get impatient before then. Thus, the wisdom that you should fan the cards instead of grouping them together to count them is sound.
Like GO said, messing them all around on the table is the best way to get them close to truely random.
Two consecutive perfect shuffles will not return a deck to its original state. A perfect shuffle followed by some kind of weird interleaved cut might do so.
First of all, yes, I’m talking about a riffle shuffle. Does any card player really do anything else? Of course spreading them out on the table would be the best way, but I’m tlaking about playing social card games here. Who the hell is going to shuffle them that way? I see I didn’t word my OP as well as I could have. Let me try again… Suppose you’re playing Hearts. At the end of the hand the players count their cards by separating the hearts into a pile and then counting them. How would that really affect the NEXT hand being dealt?
A quick note on your magician friend… using a riffle shuffle by dividing the pack into two equal halves, and doing the perfect interleave shuffle will not result in deck going back to its original order after two shuffles.
My understanding is a perfect riffle shuffle seven times randomizes the deck. Of course a perfect riflle shuffle is rare so a few more time probably wouldn’t hurt but as mentioned most people get impatient with shuffling before that (in fact tonight I was playing cards and had people telling me “enough” after 4-5 shuffles).
Some people do the “toss chunks of cards from one hand alternately off the top and bottom of the deck into the other hand” method. I usually do a combination of that and the riffle shuffle. Of course no shuffle guarantees that cards won’t repeat one hand to the next. There was an episode of the World Poker Tour (which will repeat this evening) in which the same hole cards (K8 of clubs) turned up in players’ hands three hands in a row.
Okay. I just did. Not hurrying, not taking my time. It took 26 seconds to do 7 shuffles (riffle and bridge). If that’s too long, then your card games are very different from the casual buddies-getting-together-and-socializing games that I play. Slow down and smell the bean dip.
When my friends and I play cards, it’s usually hi-lo poker games and it’s rare that the winners can split the pot in the amount of time it takes me to do 7 fast shuffles.
First off, seven riffle shuffles do not get you a perfectly random deck. It does come within 1% of random and that was the criterion that Persi Diaconis and his collaborator (whose name I have forgotten) used in the seven shuffles paper, which I once read. Second, perfect riffle shuffles don’t ever produce random decks. You have to randomize the shuffles. Take a random number of cards in each pack and then riffle random numbers of cards.
It is interesting that in bridge tournaments that use computers to deal random hands, the players are complaining that there are too many hands with weird distribution. It has been studied (many tournaments keep elaborate records going back years) and they are right. The apparent explanation is that bridge games tend to put four cards of a suit together and the shuffles often leave three and four together, which gives them to four different players. Thus the hands tend to flat distribution.
It just occurs to me that there is a flaw in this explanation since tournaments use duplicate trays and there is no particular reason for the cards to come in groups of four of the same suit. At any rate, it is hard to produce randomized decks.
Another thing that is very hard to do is to flip a coin fairly. There is a remarkable tendency for the coin to come up with the same face that you flipped it up. That is because unless your flip was perfect, it will spend much more time with the original face up than down. It is even possible to flip it in such a way that it never turns over at all. I saw a demo of this by Diaconis. He says that even he, a skilled magician, cannot tell if the coin is turning over. He said the best thing to do to get a fair flip is to reach into your pocket and pull it out randomly. This is assuming that that is what you are trying to do. The way they do in the NFL, letting the coin fall to the ground, is somewhat better.
Perfect riffle shuffling will return the cards to their original order after eight shuffles. (Anyone need proof?) By perfect, I mean that the deck is split exactly in half, and cards fall alternately, one at a time from each half. It takes a fair amount of skill to do it, but there’s no ‘trick’ involved.
InvisibleWombat, how long would it take you to shuffle an 8 deck shoe? AIUI, the famed seven shuffles refers specifically to casino play. More shuffles would increase the randomness, but also take longer. It has been calculated that seven shuffles is the optimum balance of randomness vs speed. When you’re just playing with friends, two or three shuffles should be enough.
That depends on which half of the deck you start with. If you start with the card from the bottom half on the bottom, then 8 will bring you back. But that’s a bad shuffle anyway, since it’ll never move the top or bottom card at all. Well, bad if you’re trying to play an honest game, anyway… It’s probably useful for some card tricks.
If you start with the bottom card of the top half on the bottom, then all of the cards will change position, and it takes 13 perfect shuffles to get back to your original hand. And if you do some of your perfect shuffles one way and some the other, you’re not guaranteed to ever get back to the original order.
Are there people who can actually do this? It just seems rather unlikely to me that somebody can pull off one perfect shuffle consistently, much less eight. But I suppose it’s possible–it sounds like you’re saying it is.
When I was playing poker rather frequently, is used to mix the cards by using a Faro shuffle; thinking that it made my card-handling skills appear “cool” to my tablemates because it differed from the riffle and hand-chopping method.
I learned it years earlier when doing magic as a youth. I stopped doing it when one of my tablemates made a joking accusation that I was stacking the deck when I shuffled in that manner.
This is somewhat difficult to explain without pictures, but I suspect this is the trick:
Cut the deck into two piles. Riffle shuffle them, but only so that one corner of each of the two stacks are interlaced, and so that the top card of the interlacing is from the right-hand stack. At this point, the two stacks are at an L-shaped angle (pointing away from you), with the corners interlaced. Push the top card of the right-hand stack inward (ie, with your right index finger, push the top card of the right stack towards your left hand a bit). As you do this, pull the stacks apart so that they are no longer interlaced, and straighten the angle between them. At this point, the two stacks are colinear and not interlaced. There is a gap between them, but this is obscured from the top by the one card you’ve pushed over, and from the sides by your hands. Now, lift up the left stack slightly and slide the whole thing underneath the top card as you square the deck. Square it quickly so no one catches what you’re doing!
I did some research, and apparently this type of shuffle is known as the “Faro Shuffle.” And, yes, it can be performed consistently by a skilled card manipulator. I find that quite amazing.
Faros are much easier than they look. They just take a bit of practice. Anyone willing to put the time into learning it can have it down over the course of a weekend. In the world of card sleights, I’d put the difficulty level at a 3. Doing them consisently may take a bit more effort, but that’s just continuing to practice.
Okay. I just did. Not hurrying, not taking my time. It took 26 seconds to do 7 shuffles (riffle and bridge). If that’s too long, then your card games are very different from the casual buddies-getting-together-and-socializing games that I play. Slow down and smell the bean dip.