使用NSPredicate过滤NSArray / NSDictionary

Question

I've been trying to filter this array (which is full of NSDictionaries) using NSPredicate...

I have a very small amount of code that just isn't working...

The following code should change label.text to AmyBurnett34, but it doesn't...

NSPredicate *pred = [NSPredicate predicateWithFormat:@"id = %@", [[mightyPlistDict objectForKey:@"pushesArr"] objectAtIndex:indexPath.row]];

    NSLog(@"%@",pred);

    label.text = [[[twitterInfo filteredArrayUsingPredicate:pred] lastObject] objectForKey:@"screen_name"];
    NSLog(@"%@",twitterInfo);

And here is what gets NSLoged...

2012-08-05 11:39:45.929 VideoPush[1711:707] id == "101323790"
2012-08-05 11:39:45.931 VideoPush[1711:707] (
        {
        id = 101323790;
        "screen_name" = AmyBurnett34;
    },
        {
        id = 25073877;
        "screen_name" = realDonaldTrump;
    },
        {
        id = 159462573;
        "screen_name" = ecomagination;
    },
        {
        id = 285234969;
        "screen_name" = "UCB_Properties";
    },
        {
        id = 14315150;
        "screen_name" = MichaelHyatt;
    }
)

Just for the heads up if you also NSLog this... the array is empty...

NSLog(%@,[twitterInfo filteredArrayUsingPredicate:pred]);

Answer 1

The problem is that your predicate is using comparing with a string and your content is using a number. Try this:

NSNumber *idNumber = [NSNumber numberWithLongLong:[[[mightyPlistDict objectForKey:@"pushesArr"] objectAtIndex:indexPath.row] longLongValue]];
NSPredicate *pred = [NSPredicate predicateWithFormat:@"id = %@", idNumber];

Answer 2

You don't know for sure that the value of "id" is a string - it might be a NSNumber. I suggest:

NSUInteger matchIdx = ...;
NSUInteger idx = [array indexOfObjectPassingTest:^BOOL(NSDictionary *dict, NSUInteger idx, BOOL *stop)
{
  id obj = [dict objectForKey:@"id"];
  // NSLog the class if curious using NSStringFromClass[obj class];
  NSUInteger testIdx = [obj integerValue]; // works on strings and numbers
  return testIdx == matchIdx;
}
if(idx == NSNotFound) // handle error

NSString *screenName = [[array objectAtIndex:idx] objectForKey:@"screen_name"];

Answer 3

NSPredicate is used for filtering arrays, not sorting them. To sort an array, use the sortedArrayUsingDescriptors method of NSArray.

An an example:

// Define a sort descriptor based on last name.
NSSortDescriptor *descriptor = [[NSSortDescriptor alloc] initWithKey:@"lastName" ascending:YES];    

// Sort our array with the descriptor.
NSArray *sortedArray = [originalArray sortedArrayUsingDescriptors:[NSArray arrayWithObjects:descriptor, nil]];