On May 5, 2012, at 10:06 PM, Quincey Morris wrote: > However, even in pure ASCII strings, 'localizedCaseInsensitiveCompare:' > doesn't support sorting via (say) a binary search. Strings such as "a" and > "A" are *equal* according to this method. Binary search doesn't work if > sorted elements are equal according to the comparison function.
I disagree. Binary search of a sorted array works fine if there are different keys that sort as equal; it’s just that it’ll find *one* of the equal keys, and you’d then have to look at its neighbors to find all the others. If you mean tree-based searching, that works fine too; for example, HFS+ stores the disk catalog as a b-tree and of course uses a case-insensitive comparison by default. (OK, HFS+ doesn’t allow multiple items with equivalent keys [paths], but there are b-tree storage libraries like Berkeley DB that do.) > The NSString option that apparently causes this is 'NSForcedOrderingSearch', > but the documentation doesn't really say whether this option is assumed by > 'localizedCaseInsensitiveCompare:' or not. (The documentation for > 'caseInsensitiveCompare:' implies not.) The docs for NSForcedOrderingSearch read: "Comparisons are forced to return either NSOrderedAscending or NSOrderedDescending if the strings are equivalent but not strictly equal.” In other words, it only returns 0 if the strings are identical This is definitely not true of -caseInsensitiveCompare, localized or not. In other words, if you want a stable case-insensitive sort (where equivalent strings always appear in a certain fixed order) you can’t just use -caseInsensitiveCompare:; you have to use one of the -compare: methods that takes options, and enable NSForcedOrderingSearch. —Jens _______________________________________________ Cocoa-dev mailing list (Cocoa-dev@lists.apple.com) Please do not post admin requests or moderator comments to the list. Contact the moderators at cocoa-dev-admins(at)lists.apple.com Help/Unsubscribe/Update your Subscription: https://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
