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I am trying to get the compare an object in an NSArray with two objects in two different NSArrays and i want to store the first occurence of the object and discard the next.

e.g:-

I have an Array1 where it contains objects like (20.12, 20.15, 21.4, 22.6, 23.0, 24.2, 28.7, 30.5, 30.9, 32.6, 33.7). Now i have another Array2 that contains objects like (20.00, 22.0, 28.0, 30.0, 33.0) and another Array3 that contains objects like (21.0, 24.0, 29.0, 32.0, 34.0)

Now i want to store the first objects that are in between (20.00 - 21.0, 22.0 - 24.0, 28.0 - 29.0, 30.0 - 32.0, 33.0 - 34.0). I have tried to implement this by using 

if (clickTimeInterval >= [[Array2 objectAtIndex:i] doubleValue] && clickTimeInterval <= [[Array3 objectAtIndex:i] doubleValue]) {

My clickTimeInterval is the time interval stored in my Array1. I am able to get the values but i just want to store the values that comes first and store into Array4. It looks something like Array4 = (20.12, 22.6, 24.2, 28.7, 30.5, 33.7). Can anyone please help me out on how to get this?

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  • Just Create NSMutableArray and add Cliktervel in it Commented Jun 4, 2012 at 12:40

3 Answers 3

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2

It depends on how optimized you want to be. Here's a version that re-samples "Array1" for each range. If you have a large number of objects to filter (and they are sorted), you could store the last found location to make subsequent searches quicker.

- (NSArray *)bucketTest {
    NSMutableArray *result = [NSMutableArray array];

    NSArray *samples = [NSArray arrayWithObjects:[NSNumber numberWithDouble:1.1], [NSNumber numberWithDouble:1.5], [NSNumber numberWithDouble:2.2], nil];
    NSArray *lows = [NSArray arrayWithObjects:[NSNumber numberWithDouble:1.0], [NSNumber numberWithDouble:2.0], nil];
    NSArray *highs = [NSArray arrayWithObjects:[NSNumber numberWithDouble:2.0], [NSNumber numberWithDouble:3.0], nil];
    for (int bucket = 0; bucket < [lows count]; bucket++) {
        double low = [[lows objectAtIndex:bucket] doubleValue];
        double high = [[highs objectAtIndex:bucket] doubleValue];
        for (NSNumber *sample in samples) {
            if (([sample doubleValue] >= low) && ([sample doubleValue] < high)) {
                [result addObject:sample];
                break;
            }
        }
    }
    return result;
}
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2

Improving efficiency of the first answer. Here I am assuming that all arrays are sorted

Make one more array that we will change in each iteration

NSArray *array5 = [array1 copy];

NSMutableArray *array4 = [NSMutableArray array];
for (int i=0; i < array2.count; i++) {
    NSNumber *bottom = [array2 objectAtIndex:i];
    NSNumber *top = [array3 objectAtIndex:i];
    NSPredicate *greaterThanPredicate = [NSPredicate predicateWithFormat:
                                         @"SELF > %@", bottom];
    NSMutableArray *arrayWithBiggerObjects = [NSMutableArray arrayWithArray:[array5 filteredArrayUsingPredicate:greaterThanPredicate]];

    if (arrayWithBiggerObjects.count) {
        NSNumber *lowestObject = [arrayWithBiggerObjects objectAtIndex:0];
        if ([lowestObject compare:top] == NSOrderedDescending) {
            [array4 addObject:lowestObject];
            [arrayWithBiggerObjects removeObject:lowestObject];
            array5 = arrayWithBiggerObjects;
        }
    }
}
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Comments

1

Assuming that

  1. All arrays are ordered ascending
  2. array2.count == array3.count
  3. The nth object of array2 is smaller than the nth object of array3

you can do the following

NSMutableArray *array4 = [NSMutableArray array];
for (int i=0; i < array2.count; i++) {
   NSNumber *bottom = [array2 objectAtIndex:i];
   NSNumber *top = [array3 objectAtIndex:i];
   NSPredicate *betweenPredicate = [NSPredicate predicateWithFormat:
      @"SELF > %@ && SELF < %@", bottom, top]; 
   NSArray *inRange = [array1 filteredArrayUsingPredicate:betweenPredicate];
   if (inRange.count) {
      [array4 addObject:[inRange objectAtIndex:0]];
   }
   else {
      [array4 addObject:[NSNull null]]; // or don't add anything
   }
}
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2 Comments

if (inRange.count) { [array4 addObject:[inRange firstObject]]; } In the mentioned code an NSArray doesn't declare a method with selector 'firstObject'... Can u please check it once?
Sorry, it should be objectAtIndex:0. Corrected the answer. (There is method lastObject, so I just assumed there is also one for firstObject.)

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