Question

I need to save NSStrings from an array into a .csv file in my documents directory, which is not a problem, but I don’t know how to handle the carriage return.. I specify that I want to apply a carriage return every 8 cells and this happens correctly. However when it comes to write the actual CSV file an extra unwanted comma is added after the carriage return! This is the incriminated line:

NSString *ArrayConvertedIntoStringFINAL = [FinalStringsArrayWithCarriageReturns componentsJoinedByString:@","];

How can I tell the compiler not to apply a comma after a carriage return?

Here is the complete code. Thanks guys!

//Add a Carriage Return symbol every N objects (every FREQUENCY)
int FREQUENCY = 8;

//Define String WithCarriageReturns
NSMutableArray *FinalStringsArrayWithCarriageReturns = [[NSMutableArray alloc] initWithCapacity:0];

for (int i = 1; i <= [FinalStringsArray count]; i++)
{
    NSString *readValue = [FinalStringsArray objectAtIndex:i-1];
    //Add objects to the final string
    [FinalStringsArrayWithCarriageReturns addObject:readValue];

    if ( (i % FREQUENCY) == 0) //Number is multiple of N
    {
        //Every multiple of N add the Carriage Return symbol
        [FinalStringsArrayWithCarriageReturns addObject:CarriageReturn];
    }
}
NSLog(@"+2+Broken down array strings: %@",FinalStringsArrayWithCarriageReturns);

//PROBLEM! A comma is added after the Carriage Return

//Convert Array into String
NSString *ArrayConvertedIntoStringFINAL = [FinalStringsArrayWithCarriageReturns componentsJoinedByString:@","];

Answer 1

The approach you have posted results in 2 additional copies of every string. That’s a lot of wasted memory. Here’s a simpler approach that only requires a single extra copy and no extra arrays:

int FREQUENCY = 8;

NSMutableString *csv = [NSMutableString string];

NSUInteger count = FinalStringsArray.count;
for (int i = 1; i <= count; i++) {
    NSString *readValue = FinalStringsArray[i - 1];

    // TODO - deal with possibility of 'readValue' containing a comma or carriage return
    [csv appendString:readValue];

    if ((i % FREQUENCY) == 0) { //Number is multiple of N
        [csv appendString:CarriageReturn];
    } else {
        [csv appendString:@","];
    }
}

Depending on how much data you need to write, it would be even better to write directly to a file instead of the mutable string. This would result in no extra copy of the data and would be faster than writing to the mutable string first.