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.
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