How can I simplify my nested for-loops with ReactiveCocoa? - objective-c

Question

Say I have 2 NSDictionaries that I don't know beforehand like:
NSDictionary *dictA = #{ #"key1" : #1,
#"key2" : #2 };
NSDictionary *dictB = #{ #"key1" : #"a string" };
I want to find the first match between the keys of dictB and the keys or values of dictA. Each key of dictB will either be a NSNumber or a string. If it's a number, try to find a match from the values of dictA. If it's a string, try to find a match from the keys of dictA.
Using for loops, it would looks something like this:
id match;
for (id key in dictA ) {
for (id _key in dictB {
if ( [_key is kindOfClass:NSNumber.class] && _key == dictA[key] ) {
match = _key
goto outer;
}
else if ( [_key is kindOfClass:NSString.class] && [_key isEqualToString:key] ) {
match = _key
goto outer;
}
}
};
outer:;
NSString *message = match ? #"A match was found" : #"No match was found";
NSLog(message);
How could I rewrite this with ReactiveCocoa using RACSequence and RACStream methods so it looks something like:
// shortened pseudo code:
// id match = [dictA.rac_sequence compare with dictB.rac_sequence using block and return first match];

Answer 1

You basically would like to create the cartesian product of the dictionaries and make a selection on it. There is no default operator in ReactiveCocoa that I know of that would do this for you. (In LINQ there are operators for this.) In RAC the simplest solution is to use the scanWithStart:combine: method to implement this operation. Once the cartesian is ready, the filter: and take:1 operations will produce the sequence of your choice.
NSDictionary *adic = #{#"aa":#"vb", #"ab": #"va"};
NSDictionary *bdic = #{#"ba": #"va", #"bb":#"vb"};;
RACSequence *aseq = adic.rac_keySequence;
RACSequence *bseq = bdic.rac_keySequence;
RACSequence *cartesian = [[aseq scanWithStart:nil combine:^id(id running, id next_a) {
return [bseq scanWithStart:nil combine:^id(id running, id next_b) {
return RACTuplePack(next_a, next_b);
}];
}] flatten];
RACSequence *filteredCartesian = [cartesian filter:^BOOL(RACTuple *value) {
RACTupleUnpack(NSString *key_a, NSString *key_b) = value;
// business logic with keys
return false;
}];
RACSequence *firstMatch = [filteredCartesian take:1];