NSPredicate strings greater comparision

I am trying to compare if one NSString is "greater" than other NSString and I am stuck. Actually, my NSString contains a date and want to get all these objects that are greater than it. I know I should 开发者_C百科convert it to date, but I want to keep it as NSString. Thank You!

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Something like

[string1 compare:otherString] == NSOrderedDescending