Using NSPredicate to filter an NSArray based on NSDictionary keys
Objective CCocoaNsarrayNsdictionaryNspredicateObjective C Problem Overview
I have an array of dictionaries.
I want to filter the array based on a key.
I tried this:
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(SPORT == %@)", @"Football"];
NSArray *filteredArray = [data filteredArrayUsingPredicate:predicate];
This doesn't work, I get no results. I think I'm doing something wrong. I know this is the method if "SPORT" was an ivar. I think it is probably different if it is a key.
I haven't been able to find an example however.
Thanks
Update
I added quotes around the string I am searching for.
NSPredicate *predicate = [NSPredicate predicateWithFormat:@"(SPORT == '%@')", @"Football"];
It still does not work.
Update 2
Solved it. I actually had to remove the single quotes, which seems to go against what the guide says.
My real problem is I had a nested array and I wasn't actually evaluating the dictionaries. Bone head move.
Objective C Solutions
Solution 1 - Objective C
It should work - as long as the data variable is actually an array containing a dictionary with the key SPORT
NSArray *data = [NSArray arrayWithObject:[NSMutableDictionary dictionaryWithObject:@"foo" forKey:@"BAR"]];
NSArray *filtered = [data filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"(BAR == %@)", @"foo"]];
Filtered in this case contains the dictionary.
(the %@ does not have to be quoted, this is done when NSPredicate creates the object.)
Solution 2 - Objective C
I know it's old news but to add my two cents. By default I use the commands LIKE[cd]
rather than just [c]
. The [d]
compares letters with accent symbols. This works especially well in my Warcraft App where people spell their name "Vòódòó" making it nearly impossible to search for their name in a tableview. The [d]
strips their accent symbols during the predicate. So a predicate of @"name LIKE[CD] %@", object.name
where object.name == @"voodoo"
will return the object containing the name Vòódòó.
From the Apple documentation: like[cd] means “case- and diacritic-insensitive like.”) For a complete description of the string syntax and a list of all the operators available, see Predicate Format String Syntax.
Solution 3 - Objective C
#import <Foundation/Foundation.h>
// clang -framework Foundation Siegfried.m
int
main() {
NSArray *arr = @[
@{@"1" : @"Fafner"},
@{@"1" : @"Fasolt"}
];
NSPredicate *p = [NSPredicate predicateWithFormat:
@"SELF['1'] CONTAINS 'e'"];
NSArray *res = [arr filteredArrayUsingPredicate:p];
NSLog(@"Siegfried %@", res);
return 0;
}
Solution 4 - Objective C
NSPredicate
is only available in iPhone 3.0.
You won't notice that until try to run on device.
Solution 5 - Objective C
With Swift 3, when you want to filter an array of dictionaries with a predicate based on dictionary keys and values, you may choose one of the following patterns.
NSPredicate
init(format:arguments:)
initializer
#1. Using If you come from Objective-C, init(format:arguments:)
offers a key-value coding style to evaluate your predicate.
Usage:
import Foundation
let array = [["key1": "value1", "key2": "value2"], ["key1": "value3"], ["key3": "value4"]]
let predicate = NSPredicate(format: "key1 == %@", "value1")
//let predicate = NSPredicate(format: "self['key1'] == %@", "value1") // also works
let filteredArray = array.filter(predicate.evaluate)
print(filteredArray) // prints: [["key2": "value2", "key1": "value1"]]
NSPredicate
init(block:)
initializer
#2. Using As an alternative if you prefer strongly typed APIs over stringly typed APIs, you can use init(block:)
initializer.
Usage:
import Foundation
let array = [["key1": "value1", "key2": "value2"], ["key1": "value3"], ["key3": "value4"]]
let dictPredicate = NSPredicate(block: { (obj, _) in
guard let dict = obj as? [String: String], let value = dict["key1"] else { return false }
return value == "value1"
})
let filteredArray = array.filter(dictPredicate.evaluate)
print(filteredArray) // prints: [["key2": "value2", "key1": "value1"]]
Solution 6 - Objective C
Looking at the NSPredicate reference, it looks like you need to surround your substitution character with quotes. For example, your current predicate reads: (SPORT == Football)
You want it to read (SPORT == 'Football')
, so your format string needs to be @"(SPORT == '%@')"
.