RAC: map: and flattenMap:

gistfile1.txt

RACSignal *numberSignal = @[ @1, @2, @3 ].rac_sequence.signal;

// signal of @2, @4, @6
[numberSignal map:^ id (NSNumber number) {
	return @(number.integerValue * 2);
}];

// signal of something like
// @{ @"id": @1, @"name": @"Name 1" },
// @{ @"id": @2, @"name": @"Name 2" },
// @{ @"id": @3, @"name": @"Name 3" }
[numberSignal flattenMap:^ RACSignal * (NSNumber number) {
	// -fetchUserWithId: returns a signal that fetches some JSON from web API
	return [client fetchUserWithId:number.integerValue];
}];