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 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
>
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