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Java Forum / General / November 2006what is natural order ?
TreeSet maintains its elements in their natural order, hence iterating will produce "Apple Banana Cricket " instead of "Apple Cricket Banana" what is natural order in the above ? does it want to say, treeset always sorts automatically by ALPHABATICALLY ? > TreeSet maintains its elements in their natural order, hence iterating > will produce "Apple Banana Cricket " instead of "Apple Cricket Banana" [quoted text clipped - 3 lines] > does it want to say, treeset always sorts automatically by > ALPHABATICALLY ? Yes, in this case - as it contains strings. String implements comparable, which offers natural ordering. In case of strings, the natural ordering implies alphabetical sorting. You might want to take a look at Comparable Interface for more information on this. http://java.sun.com/j2se/1.4.2/docs/api/java/lang/Comparable.html -cheers, Manish >>TreeSet maintains its elements in their natural order, hence iterating >>will produce "Apple Banana Cricket " instead of "Apple Cricket Banana" [quoted text clipped - 7 lines] > comparable, which offers natural ordering. In case of strings, the > natural ordering implies alphabetical sorting. [...] Almost. The natural ordering for String objects is their lexicographic order according to the Unicode values of their individual characters, so (for example) "Aïda" comes after "Axolotl". For an even more blatant violation of alphabetical order, note that "Zebra" precedes "aardvark". Also, "alphabetical order" varies from place to place, even if you consider only languages written in Latin alphabets. As far as I know (I'm no expert on this, just someone who once got a bit of a scolding from a person who was), everybody agrees on the ordering of the twenty-six unaccented letters, but the treatment of accented letters is subject to national and linguistic variation. See also java.text.Collator and allied classes.  SignatureEric Sosman esosman@acm-dot-org.invalid > Almost. The natural ordering for String objects is their > lexicographic order according to the Unicode values of their > individual characters, so (for example) "Aïda" comes after > "Axolotl". For an even more blatant violation of alphabetical > order, note that "Zebra" precedes "aardvark". All true, and undoubtedly all that the OP needs to know. But it may be (midly) interesting to note that -- although String /claim/ to sort lexicographically according to the Unicode code points -- they /actually/ sort by the UTF-16 values. And that doesn't produce the same sort order for Unicode characters outside the 16-bit range. > Also, "alphabetical order" varies from place to place, even > if you consider only languages written in Latin alphabets. As > far as I know (I'm no expert on this, just someone who once got > a bit of a scolding from a person who was), everybody agrees on > the ordering of the twenty-six unaccented letters, For interest: there are exceptions. Or at least, there are according to the Unicode people. Spanish (they say) traditionally considers ll to be a digraph falling between l and m. -- chris > Almost. The natural ordering for String objects is their > lexicographic order according to the Unicode values of their > individual characters, so (for example) "Aïda" comes after > "Axolotl". For an even more blatant violation of alphabetical > order, note that "Zebra" precedes "aardvark". I have allways though of natural ordering as the way we humans would order strings, e.g. string1 string2 string... string9 string10 string11 .. string20 string21 and other similar sort order, instead of the typical string1 string10 string11 ... string2 string20 string21 etc and other similar types of sorting problems Is there a name for the "human sort order"? and does there exists an implementation of it. Perhaps a name could be "semantic sort order". I realise that it would require quite a big implementation with many special case rules that in no way can be generalised and made into a single algorithm like lexical or natural orders. tom > I have allways though of natural ordering as the way we humans would order > strings, e.g. [quoted text clipped - 14 lines] > special case rules that in no way can be generalised and made into a > single algorithm like lexical or natural orders. There may be a name for the particular sorting you've shown above (though the sort order is ambiguous, because there are some corner cases you haven't demonstrated in that example), but I doubt that there exists a "human sort order", as different humans are likely to sort things in different orders. See Chris' post about how a Spanish speaking person would likely sort strings in different order than an English speaking person, for example. - Oliver Tom Forsmo wrote On 11/03/06 15:59,: >> Almost. The natural ordering for String objects is their >>lexicographic order according to the Unicode values of their [quoted text clipped - 32 lines] > special case rules that in no way can be generalised and made into a > single algorithm like lexical or natural orders. You might be interested in http://sourcefrog.net/projects/natsort/ (Yes, that's "frog" as in "Kermit.") SignatureEric.Sosman@sun.com > TreeSet maintains its elements in their natural order, hence iterating > will produce "Apple Banana Cricket " instead of "Apple Cricket Banana" > > what is natural order in the above ? It might be clearer to talk about what is NOT natural order. In some cases, you can provide a sorting algorithm with a comparator. The comparator defines an ordering. For example, you might create a Comparator<Integer> which orders all odd integers before all even integers, so that the the order of {1,2,3,4,5} would be: (1,3,5,2,4). In other words, by using a Comparator, you can invent any kind of ordering you want. When you DON'T use a comparator, it implies you want the natural ordering of the elements, instead of your custom ordering. - Oliver >TreeSet maintains its elements in their natural order, hence iterating >will produce "Apple Banana Cricket " instead of "Apple Cricket Banana" Natural order is the ordering provided by the compareTo() methods of the elements in the collection (all of which must implement Comparable). For String, this is asciibetical (more specifically, compared according to the unicode value of each character). >what is natural order in the above ? "Apple Banana Cricket". >does it want to say, treeset always sorts automatically by >ALPHABATICALLY ? No. TreeSet can store Comparable objects other than String. Each class defines it's own natural ordering in the compareTo() method. And further, no. String's natural ordering is not alphabetical, it's based on character values, meaning that if you have mixed upper and lowercase, you'd get "Banana apple cricket". If you want some other sort order, you need to instantiate the TreeMap with a Comparator that does what you want. The String.CASE_INSENSITIVE_ORDER Comparator is handy :) -- Mark Rafn dagon@dagon.net <http://www.dagon.net/> Free MagazinesGet these publications absolutely FREE for up to 12 months. There are no hidden fees and no obligation. Simply choose a title, complete the application form and submit it. Read more ...
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