对 nsdictionary 进行排序，它是如何工作的? [英] Sorting a nsdictionary, how does it work?

问题描述

我在理解这个 compare-using-selector 背后的逻辑时遇到了一些麻烦.

I'm having some trouble understanding the logic behind this compare-using-selector thing.

我有以下代码，我正在尝试提取密钥并同时对它们进行排序.但是，它不排序.无论我做什么，输出 NSArray 的顺序都不会改变.

I have the following code, I'm trying extract the Keys and sorting them at the same time. But, it does not sort. The output NSArray's order never changes no matter what I do.

NSMutableDictionary *dictToSort = [[NSMutableDictionary alloc] initWithObjectsAndKeys:@"Joe", [NSNumber numberWithInt:2], @"mark", [NSNumber numberWithInt:1], @"mdark", [NSNumber numberWithInt:3], nil];

NSArray *dictToSortKeys = [dictToSort keysSortedByValueUsingSelector:@selector(compare:)];

NSLog(@"Not Sorted" );

NSNumber *xx = dictToSortKeys[0];
NSNumber *xy = dictToSortKeys[1];
NSNumber *xz = dictToSortKeys[2];
NSLog(@"Sorted %d %d %d", xx.integerValue , xy.integerValue, xz.integerValue);

我不明白这个 compare: 函数是如何工作的.它说它返回 NSOrderedAscending、NSOrderedSame 或 NSOrderedDescending，但没有办法接收这些返回.而且，这应该神奇地工作吗?这个比较的文档很差.

I don't get how this compare: function work. It says it returns NSOrderedAscending, NSOrderedSame or NSOrderedDescending, but there is not way to receive these returns. And also, this is supposed to work magically? The documentation is quite poor for this comparison thing.

推荐答案

我认为您对 keysSortedByValueUsingSelector: 的作用感到困惑.它按值对字典条目进行排序，并按该顺序返回键.

I think you are confused about what keysSortedByValueUsingSelector: does. It sorts the dictionary entries by value, and returns the keys in that order.

您的字典包含以下条目:

Your dictionary contains these entries:

Key Value
--- -----
 1  mark
 2  Joe
 3  mdark

keysSortedByValueUsingSelector: 方法有效地按值"列对该表进行排序:

The keysSortedByValueUsingSelector: method effectively sorts that table by the "Value" column:

Key Value
--- -----
 2  Joe
 1  mark
 3  mdark

(注意Joe在mark之前，mark在mdark之前.)

(Note that Joe is alphabetically before mark and mark is alphabetically before mdark.)

然后它返回一个键数组，按照刚刚计算的顺序:@[@2,@1,@3].

Then it returns an array of the keys, in the order just computed: @[ @2, @1, @3 ].

请注意，keysSortedByValueUsingSelector: 从不比较键.它仅比较值.

Note that keysSortedByValueUsingSelector: never compares the keys. It only compares the values.

如果你想按键本身对键数组进行排序，只需这样做:

If you want to sort the key array by the keys themselves, just do this:

NSArray *dictToSortKeys = [dictToSort.allKeys
    sortedArrayUsingSelector:@selector(compare:)];

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