Well, ok. But I would call “Shuffle” a misleading misnomer, because until the user defines a shuffler function (which perversely might not, or might fail to, shuffle anything), it does not shuffle anything.
Thanks for taking the time to answer my question. Neil > On 16 Oct 2018, at 2:38 am, Chris Hopkins <cbehopk...@gmail.com> wrote: > > I've edited the example very slightly at: > https://play.golang.org/p/s7CUSbS8P3I > > Let's break this down. > Think about how you might shuffle a pack of cards, a simple way is to swap 2 > cards around at a time. As long as you exchange enough cards enough times and > both cards you chose are randomly picked, eventually you'll have shuffled the > pack. Please be happy with that as a concept before going further. > > The rand.Shuffle therefore doesn't care about what it has to shuffle. All it > "thinks" about is: swap element 2 and 7, swap element 24 and 9 etc. (the > numbers aren't important here, just that anything in an array can be shuffled > by giving these sorts of instructions). All it needs to know is how long the > array it has to shuffle is, and "who" can swap things around. I'll repeat > that as it might not be obvious. It doesn't have to know how to swap things, > it doesn;t have to know anything about the things. If I told you to shuffle > 52 cards by shouting out numbers, the exact same instruction if you were > instead shuffling 52 cars, or airplanes, or dogs; it's the number of things > in the list and the numbers given as instructions that matter. It therefore > only has to know of a function that can do this swap around. So we also pass > it what I have called swapper. Who is an agent who you say, swap 2 and 7, 24 > and 9, etc and it will do that. > So it can call swapper with i and j set to two values and swapper does the > swap. > > So how does this play into go: > Well we've declared the initial array as an array of words. > We've now declared swapper as someone who can carry out the function of > swapping any 2 items in that array, that is the item at location i gets put > at the position j was and the item at location j gets put where i was. I > explicitly declared swapper as a func that takes two integers as that's the > only thing rand.Shuffle knows or cars about the function. It just calls it a > whole bunch of times, doesn't pay attention to anything it does, it just > trusts it to do what needs to be done. > So as far as rand.Shuffle goes, it needs how many items are in the array, and > a function that it can call with two integer parameters. so we sat to > rand.shuffle what the length of the array is, and to use swapper. > > And that's it. Don't worry about how rand.Shuffle works (until you want to). > Yes it's a good bit of computer science to understand how it works, but it's > also good computer science to accept that you don't need to know how things > work under the hood either. > > If that overly wordy version helps? > > Chris >> On Monday, 15 October 2018 15:06:58 UTC+1, Neil Higgins wrote: >> Here's the doc for shuffle in math/random: >> >> func Shuffle(n int, swap func(i, j int)) >> Shuffle pseudo-randomizes the order of elements using the default Source. n >> is the number of elements. Shuffle panics if n < 0. swap swaps the elements >> with indexes i and j. >> >> >> And here's the example: >> >> package main >> >> import ( >> "fmt" >> "math/rand" >> "strings" >> ) >> >> func main() { >> words := strings.Fields("ink runs from the corners of my mouth") >> rand.Shuffle(len(words), func(i, j int) { >> words[i], words[j] = words[j], words[i] >> }) >> fmt.Println(words) >> >> } >> >> Why can't I understand a word of it? >> (This is not atypical, by the way - and not just for go - so if someone can >> educate me, I might suddenly start prospering in the software game) >> >> Issues (for me): >> Shuffle doesn't seem to swap anything (the thing you want shuffled isn't >> even an argument) >> As I read it the example, it should only swap two words (index i and j) but >> it seems to shuffle the everything >> What's this bloody "func" thing??? >> Why doesn't "swap" appear in the example? >> Yours sincerely, >> Confused > > -- > You received this message because you are subscribed to a topic in the Google > Groups "golang-nuts" group. > To unsubscribe from this topic, visit > https://groups.google.com/d/topic/golang-nuts/ICTwCqa8SgE/unsubscribe. > To unsubscribe from this group and all its topics, send an email to > golang-nuts+unsubscr...@googlegroups.com. > For more options, visit https://groups.google.com/d/optout. -- You received this message because you are subscribed to the Google Groups "golang-nuts" group. To unsubscribe from this group and stop receiving emails from it, send an email to golang-nuts+unsubscr...@googlegroups.com. For more options, visit https://groups.google.com/d/optout.
