Question

I am working on a word-based game, and I need to load my 180,000 word dictionary (1.9MB) into an array so the solving algorithm can work with it. The dictionary is simply one word per line, like this:

a
ab
abs
absolutely
etc
...

Right now I am using the following code to load that file into the array:

NSString *txtPath = [[NSBundle mainBundle] pathForResource:@"dict" ofType:@"txt"];
        NSString *stringFromFile = [[NSString alloc]
                                    initWithContentsOfFile:txtPath
                                    encoding:NSUTF8StringEncoding
                                    error:&error ];       
for (NSString *word in [stringFromFile componentsSeparatedByString:@"\r\n"]) {
            [wordsArray addObject:word];
        } 

This takes about 3-4 seconds on an iPhone 4. Probably even slower on older iOS devices. Is there a faster way to do this?

Answer 1

You can easily do this in the background, off the main thread using Grand Central Dispatch, or GCD.

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0),^(void){
        NSString *txtPath = [[NSBundle mainBundle] pathForResource:@"dict" ofType:@"txt"];
        NSString *stringFromFile = [[NSString alloc]
                                    initWithContentsOfFile:txtPath
                                    encoding:NSUTF8StringEncoding
                                    error:&error ];       
        for (NSString *word in [stringFromFile componentsSeparatedByString:@"\r\n"]) {
            [wordsArray addObject:word];
        } 
});

I wrote the enclosing dispatch code from memory, but it’s close (if not correct) and I think you get the idea.

EDIT: You can execute this code on the main thread, but what happens is a non-main-thread dispatch queue is where your code executes, thereby NOT blocking the UI.

You can improve the performance of your code here a little bit by replacing the for loop with just this:

[wordsArray setArray:[stringFromFile componentsSeparatedByString:@"\r\n"]];

There should be no need to iterate over the result from -componentsSeparatedByString: (an array) just to put them into another array. With 180K words, that should be a significant time saving right there.