Question

What is the easiest and best way in Objective-C to combine a list (NSArray) of NSStrings into a single NSString separated by commas, with the grammatically correct terminal conjunction “, and ” before the final item of the list?

NSArray *anArray = [NSArray arrayWithObjects:@"milk", @"butter", @"eggs", @"spam", nil];

From this array, I want the NSString @"milk, butter, eggs, and spam".

More generally, if the list is more than two items long, I want ", " between every item except the last and second-to-last (which should have ", and "). If the list is two items long, I want just the ' and ' with no comma. If the list is one item long, I want the single string from the array.

I like something as simple as:

NSString *newString = [anArray componentsJoinedByString:@", "];

But this of course omits the ‘and’ conjunction.

Is there a simpler and/or faster Objective-C way than the following:

- (NSString *)grammaticallyCorrectStringFromArrayOfStrings:(NSArray *)anArray {
    if (anArray == nil) return nil;
    int arrayCount = [anArray count];
    if (arrayCount == 0) return @"";
    if (arrayCount == 1) return [anArray objectAtIndex:0];
    if (arrayCount == 2) return  [anArray componentsJoinedByString:@" and "];

    // arrayCount > 2
    NSString *newString = @"";
    for (NSString *thisString in anArray) {
        if (thisString != [anArray objectAtIndex:0] && thisString != [anArray lastObject]) {
            newString = [newString stringByAppendingString:@", "];
        }
        else if (thisString == [anArray lastObject]) {
            newString = [newString stringByAppendingString:@", and "];
        }
        newString = [newString stringByAppendingString:thisString];
    }
    return newString;
}

Answer 1

For the loop, I’d probably do something like

NSMutableString *newString = [NSMutableString string];
NSUInteger lastIndex = arrayCount - 1;
[anArray enumerateObjectsUsingBlock:^(NSString *thisString, NSUInteger idx, BOOL *stop) {
    if (idx != 0)
        [newString appendString:@","];
    if (idx == lastIndex)
        [newString appendString:@" and "];

    [newString appendString:thisString];
}];

Though I guess that’s not really less lines.