Interpreting a data stream in objective c - objective-c

Question

I am getting a stream from a live feed. It looks something like this as a mutableArray:
"Columbia Heights",
E04,
"Cleveland Park",
A05
The first line is a name and the second is a station code.
I need to turn this into a dictionary that is Plist compliant.
So the result in mind would look like this:
name:
"Columbia Heights",
code:
E04,
name:
"Cleveland Park",
code:
A05
What I've written so far is this:
NSMutableDictionary *stationDict = [NSMutableDictionary dictionaryWithObjectsAndKeys:#"Name",#"name",#"Code",#"code", nil];
int i = 0;
for (i=0; i < counter; i++) {
// get names and codes for each of 3 fave stations
//[stationArray addObject:[mutableFaveArray objectAtIndex:i]];
NSString *tempName = [mutableFaveArray[i] valueForKey:#"name"];
NSString *tempCode = [mutableFaveArray[i] valueForKey:#"code"];
[stationDict setObject:tempName forKey:#"name"];
[stationDict setObject:tempCode forKey:#"code"];
}
I'm no longer getting an error, but I get as output, the same as my input.. I'm also only getting the last record..
"Cleveland Park",
A05
Updated Code:
NSMutableDictionary *stationDict = [NSMutableDictionary dictionaryWithObjectsAndKeys:#"Name",#"name",#"Code",#"code", nil];
int i = 0;
for (i=0; i < mutableFaveArray.count; i++) {
NSString *tempName = [mutableFaveArray[i] valueForKey:#"name"];
NSString *tempCode = [mutableFaveArray[i] valueForKey:#"code"];
[stationDict setObject:tempName forKey:#"name"];
[stationDict setObject:tempCode forKey:#"code"];
[stationArray addObject:stationDict];
}
This results in the last dictionary entry being saved twice..
{
code = A05;
name = "Cleveland Park";
},
{
code = A05;
name = "Cleveland Park";
}

Answer 1

The problem is that you're only creating a single dictionary, stationDict, before the for loop. You then hit the for loop, which changes the values in stationDict, adds stationDict to the stationArray, changes the values in stationDict again, adds that same dictionary to stationArray, and so on. What you end up with is an array that contains the same object repeated mutableFaveArray.count times.
The solution is to either create a new dictionary at the beginning of the body of the for loop, or add a copy of the dictionary to add to the array. So, either this:
for (i=0; i < mutableFaveArray.count; i++) {
stationDict = [NSMutableDictionary dictionary];
//...continue with the rest of your code...
or this:
//...other for loop code precedes this...
[stationArray addObject:[stationDict copy]];
}
Either approach ensures that each thing you add to the array is a dictionary that's distinct from the others you've added. As a refinement, you could probably speed up the code a little by using a non-mutable dictionary. If you have to create a new dictionary each time through the loop, you can create it with the data you want it to contain rather than changing the objects, so you don't necessarily need it to be mutable. Also, you can declare the loop variable inside the for statement, which ensures that it'll go out of scope as soon as the for terminates. Also, you can use Objective-C's notation for dictionaries:
NSMutableArray *stationArray = [NSMutableArray array];
for (int i=0; i < mutableFaveArray.count; i++) {
[stationArray addObject:#{#"name":mutableFaveArray[i][#"name"],
#"code":mutableFaveArray[i][#"code"]}];
}
You can further abbreviate that and maybe speed it up a bit using fast enumeration:
NSMutableArray *stationArray = [NSMutableArray array];
for (NSDictionary *fave in mutableFaveArray) {
[stationArray addObject:#{#"name":fave[#"name"],
#"code":fave[#"code"]}];
}
Or you can let mutableFaveArray do the enumerating for you:
__block NSMutableArray *stationArray = [NSMutableArray array];
[mutableFaveArray enumerateObjectsUsingBlock:^(id obj, NSUInteger idx, BOOL *stop))
{
[stationArray addObject:#{#"name":obj[#"name"],
#"code":obj[#"code"]}];
}];
That last one might be a bit faster, but perhaps a bit harder to read.