NSMutableArray - Query items without enumeration?

Question

Using LINQ in .Net I can select items from an array that match a particular criteria i.e. from an array called People:

var cleverPeople = People.Where(o=>o.IQ>110);

Is there anything similar I can do to an NSMutableArray? I have many items in it and enumerating it with a loop is pretty costly performance wise.

Chuck · Accepted Answer · 2009-06-15 09:01:02Z

7

See -[NSArray filteredArrayUsingPredicate:].

answered Jun 15, 2009 at 9:01

Chuck

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3 Comments

jdee Over a year ago

beautiful. exactly what I needed. NSPredicate *pred = [NSPredicate predicateWithFormat:@"isFired == NO"]; NSArray *filtered = [self.arenamap filteredArrayUsingPredicate:pred];

Lounges Over a year ago

Here's a nice write-up on NSPredicate vs LINQ. cimgf.com/2008/08/24/…

Mike Abdullah Over a year ago

Note that this will probably not be much faster than iterating the loop yourself. Fundamentally to select items from an array like this, the whole array must be iterated over somewhere along the line

ColinE · Accepted Answer · 2013-03-07 17:06:08Z

4

I have created a simple library, called Linq to ObjectiveC, which is a collection of methods that provide a Linq-style query interface. In your case you need the Linq-to-ObjectiveC where method:

NSArray* peopleWhoAreSmart = [people where:^BOOL(id person) {
    return [[person iq] intValue] > 110;
}];

This returns an array of of people where their IQ > 110.

answered Mar 7, 2013 at 17:06

ColinE

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1 Comment

Chuck Over a year ago

Nice — good tip. The lack of these obvious methods in Cocoa's collection classes is mind-boggling. (Also, funnily enough, this wouldn't have been possible when the question was originally posted, as blocks weren't around yet. Yay progress.)

Peter N Lewis · Accepted Answer · 2009-06-15 14:33:28Z

0

Another option would be to use Higher Order Messaging to implement select. For example,

NSArray* cleverPeople = [[People select] greaterIQ:110];

Where greaterIQ would be a category method on People.

answered Jun 15, 2009 at 14:33

Peter N Lewis

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Comments

Jay · Accepted Answer · 2014-05-02 14:05:41Z

0

Of course these (10.6+) days we've got nice APIs like indexOfObjectPassingTest to do things like

var smartPeople = [People indexesOfObjectsPassingTest:^BOOL(id person, NSUInteger idx, BOOL *stop)
                  {  return person.iq > 110; } ];

answered May 2, 2014 at 14:05

Jay

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