On Apr 27, 2010, at 8:06 PM, Roland King wrote:
> Graham Cox wrote:
>> On 28/04/2010, at 12:37 PM, Lynn Barton wrote:
>>> Newbie question: Consider an array of dictionary objects, all of the same
>>> class. One of the ivars of that class is an NSString which is unique for
>>> each instance. Does there already exist a method that will identify the one
>>> dictionary object that has a given value of that ivar, without me having to
>>> write code to examine all of the objects one by one? I have searched the
>>> documentation without finding such a method.
>>> Lynn Barton
>> You could use NSPredicate to "filter" your collection based on your unique
>> string property being equal to the one sought. If they are unique it will
>> return exactly one item (or none, if it doesn't exist).
>> See [NSArray filteredArrayUsingPredicate:]
>> It's unclear whether that would be actually any faster than doing a linear
>> search yourself - it might be slower, in that it wouldn't return as soon as
>> it found the item, but would always check every element.
>> --Graham
>
> I think that as Graham suggests that would be slower than searching yourself,
> but it is a method and it does exist and it's "free", so you could try that
> and if it's fast enough for you, that's great.
>
> Actually iterating the list however yourself is very simple and possibly
> only the same number of lines of code as making a predicate. (code typed in
> mail)
>
> YourObject *found = nil;
> for( YourObject *obj in yourArrayOfObjects )
> if( [ [ obj thePropertyYouWant ] isEqualToString:yourThing ] )
> {
> found = obj;
> break;
> }
> // if found isn't nil, you found one, if it is, you failed.
>
> Finally - are these all your objects and are you always looking for the same
> property of them? If so instead of dumping them into an array you could build
> a dictionary of them as you insert them, keyed by that string property, then
> go look it up later when you want it.
GREAT IDEA ! I'll try it. Thanks to you and Graham.
Lynn
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