NSPredicate of multidimensional NSArray - objective-c

Question

Given is an NSArray with objects, each of which has an NSArray with floats, stored as NSNumbers.
I am trying to create an NSPredicate to filter my main array based on the float values. So, for instance, how to get all objects that have the value 234.6 +/- 0.8 as one of the floats in the sub-array?
I can do something like this for a one-dimensional NSArray of floats:
float targetFloat = 234.6;
float delta = 0.8;
filterPredicate = [NSPredicate predicateWithFormat: #"myFloat > %f AND myFloat < %f", (targetFloat - delta), (targetFloat + delta)];
filteredArray = [originalArray filteredArrayUsingPredicate: filterPredicate];
But how do I change it for my 2D NSArray with NSNumbers?

Answer 1

You can use "SELF[index]" in a predicate to access specific elements of the sub-array.
The following predicate finds all sub-arrays where the first element is in the
specified range:
float lowValue = 1.5;
float hiValue = 2.5;
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"SELF[0] > %f AND SELF[0] < %f", lowValue, hiValue];
NSArray *filtered = [array filteredArrayUsingPredicate:predicate];
If you want to find the sub-arrays that contain any number in the specified range, use
NSPredicate *predicate = [NSPredicate predicateWithFormat:#"ANY SELF BETWEEN %#", #[#(lowValue), #(hiValue)]];

Answer 2

Your predicate can access the object's property that holds the array by name; I've called this list in the example below. Then use the ANY keyword to check all the values in the array, and BETWEEN to find out if those values are within your chosen range.
#import <Foundation/Foundation.h>
#interface Grumolo : NSObject
#property (copy, nonatomic) NSArray * list;
#end
#implementation Grumolo
- (NSString *)description
{
return [NSString stringWithFormat:#"%#: %p, list: %#", NSStringFromClass([self class]), self, [self list]];
}
#end
int main(int argc, const char * argv[])
{
#autoreleasepool {
float target = 234;
float delta = 0.8;
NSPredicate * p = [NSPredicate predicateWithFormat:#"ANY list BETWEEN %#", #[#(target-delta), #(target+delta)]];
NSArray * yes = #[#234, #10, #100];
NSArray * yes2 = #[#0, #16, #234];
NSArray * no = #[#1, #2, #3];
Grumolo * g1 = [Grumolo new];
[g1 setList:yes];
Grumolo * g2 = [Grumolo new];
[g2 setList:yes2];
Grumolo * g3 = [Grumolo new];
[g3 setList:no];
NSLog(#"%#", [#[g1, g2, g3] filteredArrayUsingPredicate:p]);
}
return 0;
}
You might also like to try predicateWithBlock:, which would let you express what you're trying to do with a traditional loop over each array, returning YES if you find an element that meets your criteria and NO if you exhaust the list.
NSPredicate * pb = [NSPredicate predicateWithBlock:^BOOL(Grumolo * evaluatedObject, NSDictionary *bindings) {
NSArray * list = [evaluatedObject list];
__block BOOL result = NO;
[list enumerateObjectsUsingBlock:^(NSNumber * obj, NSUInteger idx, BOOL *stop) {
BOOL moreThanLower = (NSOrderedDescending == [obj compare:#(target-delta)]);
BOOL lessThanUpper = (NSOrderedAscending == [obj compare:#(target+delta)]);
if( moreThanLower && lessThanUpper ){
*stop = YES;
result = YES;
return;
}
}];
return result;
}];