Question

I am trying to filter out an array of strings based on their length. I’m completely new to Objective C and OOP in general.

wordList=[[stringFile componentsSeparatedByCharactersInSet:[NSCharacterSetnewlineCharacterSet]] mutableCopy];
for (int x=0; x<[wordList count]; x++) {
    if ([[wordList objectAtIndex:x] length] != 6) {
        [wordList removeObjectAtIndex:x];
    }else {
       NSLog([wordList objectAtIndex:x]);
    }
}

for (int x=0; x<[wordList count]; x++) {
    NSLog([wordList objectAtIndex:x]);
}

The NSLog in the else statement will only output 6 letter words, but the second NSLog outputs the entire array. What am I missing here? Also any general pointers to clean up/improve the code are appreciated.

Answer 1

The problem with your code is that when you remove an item at index x and move to the next index x++, the item that was at x+1 is never examined.

The best way of filtering a mutable array is using the filterUsingPredicate: method. Here is how you use it:

wordList=[[stringFile
    componentsSeparatedByCharactersInSet:[NSCharacterSetnewlineCharacterSet]]
    mutableCopy];
[wordList filterUsingPredicate:
    [NSPredicate predicateWithBlock:^BOOL(id evaluatedObject, NSDictionary * bindings) { 
        return [evaluatedObject length] == 6; // YES means "keep"
    }]];