filtering NSArray into a new NSArray in Objective-C

Now task queues can be used for running batch processing or scheduled tasks

I have an NSArray and I'd like to create a new NSArray with objects from the original array that meet certain criteria. The criteria is decided by a function that returns a BOOL.

Edit:

I can create an NSMutableArray, iterate through the source array and copy over the objects that the filter function accepts and then create an immutable version of it.

Is there a better way?

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最佳答案

One of the compelling reasons I have come across for using Google App Engine is its integration with Google Apps for your domain. Essentially it allows you to create custom, managed web applications that are restricted to the (controlled) logins of your domain.

NSArray and NSMutableArray provide methods to filter array contents. NSArray provides filteredArrayUsingPredicate: which returns a new array containing objects in the receiver that match the specified predicate. NSMutableArray adds filterUsingPredicate: which evaluates the receiver’s content against the specified predicate and leaves only objects that match. These methods are illustrated in the following example.

NSMutableArray *array =
[NSMutableArray arrayWithObjects:@"Bill", @"Ben", @"Chris", @"Melissa", nil];


NSPredicate *bPredicate =
[NSPredicate predicateWithFormat:@"SELF beginswith[c] 'b'"];
NSArray *beginWithB =
[array filteredArrayUsingPredicate:bPredicate];
// beginWithB contains { @"Bill", @"Ben" }.


NSPredicate *sPredicate =
[NSPredicate predicateWithFormat:@"SELF contains[c] 's'"];
[array filteredArrayUsingPredicate:sPredicate];
// array now contains { @"Chris", @"Melissa" }
till fast despite the new language). I ran into very little that led me to believe that I wouldn't be able to accomplish my task. Instead I have a fairly positive impression of the functionality and features.

Most of my experience with this code was building a simple time/task tracking application. The template engine was simple and yet made a multi-page application very approachable. The login/user awareness api is similarly useful. I was able to make a public page/private page paradigm without too much issue. (a user would log in to see the private pages. An anonymous user was only shown the public page.)

That is my experience with it. Perhaps it doesn't represent more than an unfinished toy project, but it does represent an informed trial of the platform, and I hope that helps.

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I think App Engine is pretty cool for small projects at this point. There's a lot to be said for never having to worry about hosting. The API also pushes you in the direction of building scalable apps, which is good practice.

  • app-engine-patch is a good layer between Django and App Engine, enabling the use of the auth app and more.

    • In some category define your method that uses your function

    @implementation BaseClass (SomeCategory)
- (BOOL)myMethod {
return someComparisonFunction(self, whatever);
}
@end
  • Google have promised an SLA and pricing model by the end of 2008.

    • Then wherever you'll be filtering:

    - (NSArray *)myFilteredObjects {
NSPredicate *pred = [NSPredicate predicateWithFormat:@"myMethod = TRUE"];
return [myArray filteredArrayUsingPredicate:pred];
}
  • Requests must complete in 10 seconds, sub-requests to web services required to complete in 5 seconds. This forces you to design a fast, lightweight application, off-loading serious processing to other platforms (e.g. a hosted service or an EC2 instance).

    • Of course, if your function only compares against properties reachable from within your class it may just be easier to convert the function's conditions to a predicate string.

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Want somebody else to write that category, test it, etc.? Check out BlocksKit (array docs). And there are many more examples to be found by, say, searching for e.g. "nsarray block category select".

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Based on an answer by Clay Bridges, here is an example of filtering using blocks (change yourArray to your array variable name and testFunc to the name of your testing function):

yourArray = [yourArray objectsAtIndexes:[yourArray indexesOfObjectsPassingTest:^BOOL(id obj, NSUInteger idx, BOOL *stop) {
return [self testFunc:obj];
}]];
ith. Building the site was easy and straightforward and they have lots of helpful advice on the site.

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3)select * from tbl where column1 like '%a%' -->

[NSMutableArray arrayWithArray:[arr filteredArrayUsingPredicate:predicate]];

It's been a while since I've had to do any HTML-like code in Vim, but recently I came across this again. Say I'm writing some simple HTML:

<html><head><title>This is a title</title></head></html>

I hope this helps

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There are loads of ways to do this, but by far the neatest is surely using [NSPredicate predicateWithBlock:]:

NSArray *filteredArray = [array filteredArrayUsingPredicate:[NSPredicate predicateWithBlock:^BOOL(id object, NSDictionary *bindings) {
return [object shouldIKeepYou];  // Return YES for each object you want in filteredArray.
}]];

I think that's about as concise as it gets.

Swift:

For those working with NSArrays in Swift, you may prefer this even more concise version:

let filteredArray = array.filter { $0.shouldIKeepYou() }

filter is just a method on Array (NSArray is implicitly bridged to Swift’s Array). It takes one argument: a closure that takes one object in the array and returns a Bool. In your closure, just return true for any objects you want in the filtered array.

reball.net/projects/markdown/" rel="noreferrer">Markdown and use %! to filter your Vim buffer through the Markdown processor of your choice :)

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Checkout this library

I find using the xmledit plugin pretty useful. it adds two pieces of functionality:

    https://github.com/BadChoice/Collection

  1. When you open a tag (e.g. type <p>), it expands the tag as soon as you type the closing > into <p></p> and places the cursor inside the tag in insert mode.

    2. It comes with lots of easy array functions to never write a loop again

    So you can just do:

    NSArray* youngHeroes = [self.heroes filter:^BOOL(Hero *object) {
return object.age.intValue < 20;
}];

  2. If you then immediately type another > (e.g. you type <p>>), it expands that into

    or

    NSArray* oldHeroes = [self.heroes reject:^BOOL(Hero *object) {
return object.age.intValue < 20;
}];
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<p>

The Best and easy Way is to create this method And Pass Array And Value:

- (NSArray *) filter:(NSArray *)array where:(NSString *)key is:(id)value{
NSMutableArray *temArr=[[NSMutableArray alloc] init];
for(NSDictionary *dic in self)
if([dic[key] isEqual:value])
[temArr addObject:dic];
return temArr;
}
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</p>

Another category method you could use:

- (NSArray *) filteredArrayUsingBlock:(BOOL (^)(id obj))block {
NSIndexSet *const filteredIndexes = [self indexesOfObjectsPassingTest:^BOOL (id _Nonnull obj, NSUInteger idx, BOOL *_Nonnull stop) {
return block(obj);
}];


return [self objectsAtIndexes:filteredIndexes];
}

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