How to filter NSDictionary by substring in its keys?

Question

Say I have an NSDictionary and its keys are like this:

1. @"123_000"
2. @"223_000"
3. @"123_111"
4. @"223_111"

and so on. I want to get a NSArray or NSSet of all values whose corresponding keys contain substring @"123".

Of course I can just loop over the NSDictionary, but I suspect that there must be a less code heavy approach, probably involving KVC or NSPredicate, but I'm not really good in either of them.

Answer 1

Yes, use NSPredicate.

First get allKeys from the dictionary. Then use filteredArrayUsingPredicate: to get the list of keys you want. Then use objectsForKeys:notFoundMarker: with your resulting array of keys to get the associated objects (the not found marker isn't an issue as we know all keys exist).

Answer 2

To correct the answer of VaaChar:

In my example, I have a dictionary with keys and values only (vegan : 1, steak : 2, ...)

To check if my string is within these keys, I use:

NSPredicate *predicate  = [NSPredicate predicateWithFormat:@"SELF CONTAINS %@", keyword];
NSArray *categories     = [[self.categoriesAndIDs allKeys] filteredArrayUsingPredicate:predicate];

SELF represents the current object of the given array, in my case [self.categoriesAndIDs allKeys] so every string within the array will be checked for my "keyword", e.g. "steak" or "st" and the result will be an array with a string called "steak".

Answer 3

You could use something like this:

NSArray *resultArray = [[mainDict allValues] filteredArrayUsingPredicate:[NSPredicate predicateWithFormat:@"self.@allKeys CONTAINS[c] %@", @"123"]];

"self.@allKeys" should return all keys of your dictionary and "CONTAINS[c] %@" checks if the key contains "123".