objective-c 打乱 NSMutableArray 的最佳方法是什么？
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What's the Best Way to Shuffle an NSMutableArray?
提问by Kristopher Johnson
If you have an NSMutableArray, how do you shuffle the elements randomly?
如果你有一个NSMutableArray，你如何随机打乱元素？
(I have my own answer for this, which is posted below, but I'm new to Cocoa and I'm interested to know if there is a better way.)
（对此我有自己的答案，下面发布，但我是 Cocoa 的新手，我很想知道是否有更好的方法。）
Update: As noted by @Mukesh, as of iOS 10+ and macOS 10.12+, there is an -[NSMutableArray shuffledArray]method that can be used to shuffle. See https://developer.apple.com/documentation/foundation/nsarray/1640855-shuffledarray?language=objcfor details. (But note that this creates a new array, rather than shuffling the elements in place.)
更新：正如@Mukesh 所指出的，从 iOS 10+ 和 macOS 10.12+ 开始，有一种-[NSMutableArray shuffledArray]方法可用于随机播放。有关详细信息，请参阅https://developer.apple.com/documentation/foundation/nsarray/1640855-shuffledarray?language=objc。（但请注意，这会创建一个新数组，而不是原地打乱元素。）
采纳答案by Kristopher Johnson
You don't need the swapObjectAtIndex method. exchangeObjectAtIndex:withObjectAtIndex:already exists.
您不需要 swapObjectAtIndex 方法。exchangeObjectAtIndex:withObjectAtIndex:已经存在。
回答by Kristopher Johnson
I solved this by adding a category to NSMutableArray.
我通过向 NSMutableArray 添加一个类别来解决这个问题。
Edit:Removed unnecessary method thanks to answer by Ladd.
编辑：由于 Ladd 的回答，删除了不必要的方法。
Edit:Changed (arc4random() % nElements)to arc4random_uniform(nElements)thanks to answer by Gregory Goltsov and comments by miho and blahdiblah
编辑：更改(arc4random() % nElements)到arc4random_uniform(nElements)由格雷戈里Goltsov和评论感谢答案由美穗和blahdiblah
Edit:Loop improvement, thanks to comment by Ron
编辑：循环改进，感谢 Ron 的评论
Edit:Added check that array is not empty, thanks to comment by Mahesh Agrawal
编辑：添加检查数组不为空，感谢 Mahesh Agrawal 的评论
// NSMutableArray_Shuffling.h
#if TARGET_OS_IPHONE
#import <UIKit/UIKit.h>
#else
#include <Cocoa/Cocoa.h>
#endif
// This category enhances NSMutableArray by providing
// methods to randomly shuffle the elements.
@interface NSMutableArray (Shuffling)
- (void)shuffle;
@end
// NSMutableArray_Shuffling.m
#import "NSMutableArray_Shuffling.h"
@implementation NSMutableArray (Shuffling)
- (void)shuffle
{
NSUInteger count = [self count];
if (count <= 1) return;
for (NSUInteger i = 0; i < count - 1; ++i) {
NSInteger remainingCount = count - i;
NSInteger exchangeIndex = i + arc4random_uniform((u_int32_t )remainingCount);
[self exchangeObjectAtIndex:i withObjectAtIndex:exchangeIndex];
}
}
@end
回答by gregoltsov
Since I can't yet comment, I thought I'd contribute a full response. I modified Kristopher Johnson's implementation for my project in a number of ways (really trying to make it as concise as possible), one of them being arc4random_uniform()because it avoids modulo bias.
由于我还不能发表评论，我想我会做出完整的回应。我以多种方式为我的项目修改了 Kristopher Johnson 的实现（真的试图使其尽可能简洁），其中之一是arc4random_uniform()因为它避免了modulo bias。
// NSMutableArray+Shuffling.h
#import <Foundation/Foundation.h>
/** This category enhances NSMutableArray by providing methods to randomly
* shuffle the elements using the Fisher-Yates algorithm.
*/
@interface NSMutableArray (Shuffling)
- (void)shuffle;
@end
// NSMutableArray+Shuffling.m
#import "NSMutableArray+Shuffling.h"
@implementation NSMutableArray (Shuffling)
- (void)shuffle
{
NSUInteger count = [self count];
for (uint i = 0; i < count - 1; ++i)
{
// Select a random element between i and end of array to swap with.
int nElements = count - i;
int n = arc4random_uniform(nElements) + i;
[self exchangeObjectAtIndex:i withObjectAtIndex:n];
}
}
@end
回答by andreacipriani
If you import GameplayKit, there is a shuffledAPI:
如果您 import GameplayKit，则有一个shuffledAPI：
https://developer.apple.com/reference/foundation/nsarray/1640855-shuffled
https://developer.apple.com/reference/foundation/nsarray/1640855-shuffled
let shuffledArray = array.shuffled()
回答by C?ur
A slightly improved and concise solution (compared to the top answers).
一个稍微改进和简洁的解决方案（与顶级答案相比）。
The algorithm is the same and is described in literature as "Fisher-Yates shuffle".
该算法是相同的，在文献中被描述为“ Fisher-Yates shuffle”。
In Objective-C:
在 Objective-C 中：
@implementation NSMutableArray (Shuffle)
// Fisher-Yates shuffle
- (void)shuffle
{
for (NSUInteger i = self.count; i > 1; i--)
[self exchangeObjectAtIndex:i - 1 withObjectAtIndex:arc4random_uniform((u_int32_t)i)];
}
@end
In Swift 3.2 and 4.x:
在 Swift 3.2 和 4.x 中：
extension Array {
/// Fisher-Yates shuffle
mutating func shuffle() {
for i in stride(from: count - 1, to: 0, by: -1) {
swapAt(i, Int(arc4random_uniform(UInt32(i + 1))))
}
}
}
In Swift 3.0 and 3.1:
在 Swift 3.0 和 3.1 中：
extension Array {
/// Fisher-Yates shuffle
mutating func shuffle() {
for i in stride(from: count - 1, to: 0, by: -1) {
let j = Int(arc4random_uniform(UInt32(i + 1)))
(self[i], self[j]) = (self[j], self[i])
}
}
}
Note: A more concise solution in Swift is possible from iOS10 using GameplayKit.
回答by C?ur
This is the simplest and fastest way to shuffle NSArrays or NSMutableArrays (object puzzles is a NSMutableArray, it contains puzzle objects. I've added to puzzle object variable index which indicates initial position in array)
这是打乱 NSArrays 或 NSMutableArrays 的最简单和最快的方法（对象拼图是一个 NSMutableArray，它包含拼图对象。我已添加到拼图对象变量索引中，该变量索引指示数组中的初始位置）
int randomSort(id obj1, id obj2, void *context ) {
// returns random number -1 0 1
return (random()%3 - 1);
}
- (void)shuffle {
// call custom sort function
[puzzles sortUsingFunction:randomSort context:nil];
// show in log how is our array sorted
int i = 0;
for (Puzzle * puzzle in puzzles) {
NSLog(@" #%d has index %d", i, puzzle.index);
i++;
}
}
log output:
日志输出：
#0 has index #6
#1 has index #3
#2 has index #9
#3 has index #15
#4 has index #8
#5 has index #0
#6 has index #1
#7 has index #4
#8 has index #7
#9 has index #12
#10 has index #14
#11 has index #16
#12 has index #17
#13 has index #10
#14 has index #11
#15 has index #13
#16 has index #5
#17 has index #2
you may as well compare obj1 with obj2 and decide what you want to return possible values are:
您也可以将 obj1 与 obj2 进行比较，并决定要返回的可能值是：
- NSOrderedAscending = -1
- NSOrderedSame = 0
- NSOrderedDescending = 1
- NSOrderedAscending = -1
- NSOrderedSame = 0
- NSOrderedDescending = 1
回答by Denis Kutlubaev
There is a nice popular library, that has this method as it's part, called SSToolKit in GitHub. File NSMutableArray+SSToolkitAdditions.h contains shuffle method. You can use it also. Among this, there seem to be tons of useful things.
有一个很好的流行库，它有这个方法作为它的一部分，在 GitHub 中称为SSToolKit。文件 NSMutableArray+SSToolkitAdditions.h 包含 shuffle 方法。你也可以使用它。其中，似乎有很多有用的东西。
The main page of this library is here.
这个图书馆的主页在这里。
If you use this, your code will be like this:
如果你使用它，你的代码将是这样的：
#import <SSCategories.h>
NSMutableArray *tableData = [NSMutableArray arrayWithArray:[temp shuffledArray]];
This library also has a Pod (see CocoaPods)
这个库也有一个 Pod（见 CocoaPods）
回答by C?ur
From iOS 10, you can use NSArray shuffled()from GameplayKit. Here is an helper for Array in Swift 3:
从 iOS 10 开始，您可以使用GameplayKit 中的NSArrayshuffled()。这是 Swift 3 中 Array 的一个助手：
import GameplayKit
extension Array {
@available(iOS 10.0, macOS 10.12, tvOS 10.0, *)
func shuffled() -> [Element] {
return (self as NSArray).shuffled() as! [Element]
}
@available(iOS 10.0, macOS 10.12, tvOS 10.0, *)
mutating func shuffle() {
replaceSubrange(0..<count, with: shuffled())
}
}
回答by Gamma-Point
If elements have repeats.
如果元素有重复。
e.g. array: A A A B B or B B A A A
例如阵列：AAAB 或 BBAAA
only solution is: A B A B A
唯一的解决办法是：ABABA
sequenceSelectedis an NSMutableArray which stores elements of class obj, which are pointers to some sequence.
sequenceSelected是一个 NSMutableArray，它存储类 obj 的元素，这些元素是指向某个序列的指针。
- (void)shuffleSequenceSelected {
[sequenceSelected shuffle];
[self shuffleSequenceSelectedLoop];
}
- (void)shuffleSequenceSelectedLoop {
NSUInteger count = sequenceSelected.count;
for (NSUInteger i = 1; i < count-1; i++) {
// Select a random element between i and end of array to swap with.
NSInteger nElements = count - i;
NSInteger n;
if (i < count-2) { // i is between second and second last element
obj *A = [sequenceSelected objectAtIndex:i-1];
obj *B = [sequenceSelected objectAtIndex:i];
if (A == B) { // shuffle if current & previous same
do {
n = arc4random_uniform(nElements) + i;
B = [sequenceSelected objectAtIndex:n];
} while (A == B);
[sequenceSelected exchangeObjectAtIndex:i withObjectAtIndex:n];
}
} else if (i == count-2) { // second last value to be shuffled with last value
obj *A = [sequenceSelected objectAtIndex:i-1];// previous value
obj *B = [sequenceSelected objectAtIndex:i]; // second last value
obj *C = [sequenceSelected lastObject]; // last value
if (A == B && B == C) {
//reshufle
sequenceSelected = [[[sequenceSelected reverseObjectEnumerator] allObjects] mutableCopy];
[self shuffleSequenceSelectedLoop];
return;
}
if (A == B) {
if (B != C) {
[sequenceSelected exchangeObjectAtIndex:i withObjectAtIndex:count-1];
} else {
// reshuffle
sequenceSelected = [[[sequenceSelected reverseObjectEnumerator] allObjects] mutableCopy];
[self shuffleSequenceSelectedLoop];
return;
}
}
}
}
}
回答by fcortes
Kristopher Johnson's answeris pretty nice, but it's not totally random.
克里斯托弗·约翰逊的回答非常好，但并非完全随机。
Given an array of 2 elements, this function returns always the inversed array, because you are generating the range of your random over the rest of the indexes. A more accurate shuffle()function would be like
给定一个包含 2 个元素的数组，此函数始终返回反向数组，因为您正在生成其余索引的随机范围。一个更准确的shuffle()函数会像
- (void)shuffle
{
NSUInteger count = [self count];
for (NSUInteger i = 0; i < count; ++i) {
NSInteger exchangeIndex = arc4random_uniform(count);
if (i != exchangeIndex) {
[self exchangeObjectAtIndex:i withObjectAtIndex:exchangeIndex];
}
}
}
