Question

I am creating a very long string by formatting NSNumbers in four different arrays:

NSString *datos = @"";

for (NSInteger counter = 0; counter < [latOut count]; counter++) {
    datos = [datos stringByAppendingString:[NSString stringWithFormat:@"%.0005f,", [[latOut objectAtIndex:counter] floatValue]]];
    datos = [datos stringByAppendingString:[NSString stringWithFormat:@"%.0005f,", [[lonOut objectAtIndex:counter] floatValue]]];
    datos = [datos stringByAppendingString:[NSString stringWithFormat:@"%ld,", [[tipoOut objectAtIndex:counter] integerValue]]];
    datos = [datos stringByAppendingString:[NSString stringWithFormat:@"%ld\n", [[velocidadOut objectAtIndex:counter] integerValue]]];
}

NSString *curDir = [[NSFileManager defaultManager] currentDirectoryPath];

NSString *path = @"";
path = [path stringByAppendingPathComponent:curDir];
path = [path stringByAppendingPathComponent:@"data.csv"];

// Y luego lo grabamos
[datos writeToFile:path atomically:YES encoding:NSASCIIStringEncoding error:&error];

The count is 18,000 entries, and this loop takes almost 2 minutes to complete.

How could I make this much faster?

Answer 1

Your memory consumption is also likely mindblowing. Use a mutable string instead of creating thousands of temporary strings:

NSMutableString *datos = [NSMutableString string];

for (NSInteger counter = 0; counter < [latOut count]; counter++) {
    [datos appendFormat:@"%.0005f, %.0005f, %ld, %ld\n", [[latOut objectAtIndex:counter] floatValue], 
                                                         [[lonOut objectAtIndex:counter] floatValue], 
                                                         [[tipoOut objectAtIndex:counter] integerValue], 
                                                         [[velocidadOut objectAtIndex:counter] integerValue]];
}