Re: Selecting an object based on the value of one of its attributes
Roland, the application in question uses Core Data. To build a dictionary as
you suggest, I will need to wait until the array controller loads its content,
then iterate over all members of the array, putting the property in question
and the array index into the dictionary. How can I know immediately (without
any user action) that the content has finished loading? I can't use
awakeFromNib, as the content has not yet been loaded when that method is called.
--Lynn
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.
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Re: Selecting an object based on the value of one of its attributes
On Mon, May 3, 2010 at 3:24 PM, Lynn Barton lynnbar...@mac.com wrote: Roland, the application in question uses Core Data. To build a dictionary as you suggest, I will need to wait until the array controller loads its content, then iterate over all members of the array, putting the property in question and the array index into the dictionary. How can I know immediately (without any user action) that the content has finished loading? I can't use awakeFromNib, as the content has not yet been loaded when that method is called. This sounds like something that should be happening at the model layer, not at the controller layer. --Kyle Sluder ___ 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: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: Selecting an object based on the value of one of its attributes
Le 28 avr. 2010 à 04:37, Lynn Barton a écrit : 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? Use a hash code. That's the way NSDictionary class search for keys. It is way faster than simple linear search, especially if you have thousands of elements. But it is more code and memory expensive. Vincent ___ 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: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Selecting an object based on the value of one of its attributes
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 ___ 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: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: Selecting an object based on the value of one of its attributes
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 ___ 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: http://lists.apple.com/mailman/options/cocoa-dev/archive%40mail-archive.com This email sent to arch...@mail-archive.com
Re: Selecting an object based on the value of one of its attributes
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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Re: Selecting an object based on the value of one of its attributes
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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