title: how to verify if an element exsit or not in an NSMutubleArray
body: <p>I'm new to objective-c.
  I have an NSMutableArray . I wrote this:</p>
  
  <pre><code>for (int i=0; i&lt;[allCombinations count]; i++)
  {
      NSString *date = [[allCombinations objectAtIndex:i] objectForKey:@"keydate"];
      NSString *cachdepeDate = [date substringToIndex:8];
  }
  </code></pre>
  
  <p>How can i see if cachdepeDate is alrady exsit in my NSMutbleArray?</p>
  
  <p>If it is not exist how do I add it? </p>
  
  <p>Should I make for loop, or there is a method for this? </p>
  
  <p>Can i sort the NSMutbleArray? </p>
  
  <p>Dates are in this format: "20110531" "YYYYMMDD". 
  Thank you!</p>