What does sorting mean in double-byte languages?

Question

I have some code that sorts table columns by object properties. It occurred to me that in Japanese or Chinese (non-alphabetical languages), the strings that are sent to the sort function would be compared the way an alphabetical language would.

Take for example a list of Japanese surnames:

寿拘
松坂
松井
山田
藤本

In English, these would be Suzuki, Matsuzaka, Matsui, Yamada, Fujimoto.

When I sort the above list via Javascript, the result is:

寿拘
山田
松井
松坂
藤本

(Suzuki, Yamada, Matsui, Matsuzaka, Fujimoto) This is different from the ordering of the Japanese syllabary, which would order the list (phonetically) as Suzuki, Fujimoto, Matsui, Matsuzaka, Yamada.

What I want to know is:

1. Does one double-byte character really get compared against the other in a sort function?
2. What really goes on in such a sort?
3. (Extra credit) Does the result of such a sort mean anything at all? Does the concept of sorting really work in Asian (and other) languages? If so, what does it mean and what should one strive for in creating a compare function for those languages?

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ADDENDUM TO SUMMARIZE ANSWERS AND DRAW CONCLUSIONS:

First, thanks to all who contributed to the discussion. This has been very informative and helpful. Special shout-outs to bobince, Lie Ryan, Gumbo, Jeffrey Zheng, and Larry K, for their in-depth and thoughtful analyses. I awarded the check mark to Larry K for pointing me toward a solution my question failed to foresee, but I up-ticked every answer I found useful.

The consensus appears to be that:

1. Chinese and Japanese character strings are sorted by Unicode code points, and their ordering may be predicated on a rationale that may be in some way intelligible to knowledgeable readers but is not likely to be of much practical value in helping users to find the information they're seeking.

2. The kind of compare function that would be required to make a sort semantically or phonetically useful is far too cumbersome to consider pursuing, especially since the results would probably be less than satisfactory, and in any case the comparison algorithms would have to be changed for each language. Best just to allow the sort to proceed without even attempting a compare function.

3. I was probably asking the wrong question here. That is, I was thinking too much "inside the box" without considering that the real question is not how do I make sorting useful in these languages, but how do I provide the user with a useful way of finding items in a list. Westerners automatically think of sorting for this purpose, and I was guilty of that. Larry K pointed me to a Wikipedia article that suggests a filtering function might be more useful for Asian readers. This is what I plan to pursue, as it's at least as fast as sorting, client-side. I will keep the column sorting because it's well understood in Western languages, and because speakers of any language would find the sorting of dates and other numerical-based data types useful. But I will also add that filtering mechanism, which would be useful in long lists for any language.

Answer 1

Yes, the characters get compared. They are usually compared based on their Unicode code points, though, which are quite different between hiragana and kanji -- making the sort potentially useless in Japanese. (Kanji borrowed from Chinese, but the order they'd appear in Chinese doesn't correspond to the order of the hiragana that'd represent the same meaning). There are collations that could render some of the characters "equal" for comparison purposes, but i don't know if there's one that'll consider a kanji to be equivalent to the hiragana that'd comprise its pronunciation -- especially since a character can have a number of different pronunciations.

In Chinese or Korean, or other languages that don't have 3 different alphabets (one of which is quite irregular), it'd probably be less of an issue.

Answer 2

Those are sorted by codepoint value, ascending. This is certainly meaningless for human readers. It's not impossible to devise a sensible sorting scheme for Japanese, but sorting Chinese characters is hard (partly because we don't necessarily know whether we're looking at Japanese or Chinese), and lot of programmers punt to this solution.

Answer 3

Strings are compared character by character where the code point value defines the order:

The comparison of strings uses a simple lexicographic ordering on sequences of code point value values. There is no attempt to use the more complex, semantically oriented definitions of character or string equality and collating order defined in the Unicode specification. Therefore strings that are canonically equal according to the Unicode standard could test as unequal. In effect this algorithm assumes that both strings are already in normalised form.

If you need more than this, you will need to use a string comparison that can take collations into account.

Answer 4

Recall that in JavaScript, you can pass into sort() a function in which you can implement sort yourself, in order to achieve a sort that matters to humans:

myarray.sort(function(a,b){

//return 0, 1, or -1 based on the comparison of the two strings

});

Answer 5

Does one double-byte character really get compared against the other in a sort function?

The native String type in JavaScript is based on UTF-16 code units, and that's what gets compared. For characters in the Basic Multilingual Plane (which all these are), this is the same as Unicode code points.

The term ‘double-byte’ as in encodings like Shift-JIS has no meaning in a web context: DOM and JavaScript strings are natively Unicode, the original bytes in the encoded page received by the browser are long gone.

Does the result of such a sort mean anything at all?

Little. Unicode code points do not claim to offer any particular ordering... for one, because there is no globally-accepted ordering. Even for the most basic case of ASCII Latin characters, languages disagree (eg. on whether v and w are the same letter, or whether the uppercase of i is I or İ). And CJK gets much gnarlier than that.

The main Unicode CJK Unified Ideographs block happens to be ordered by radical and number of strokes (Kangxi dictionary order), which may be vaguely useful. But use characters from any of the other CJK extension blocks, or mix in some kana, or romaji, and there will be no meaningful ordering between them.

The Unicode Consortium do attempt to define some general ordering rules, but it's complex and not generally attempted at a language level. Systems that really need language-sensitive sorting abilities (eg. OSes, databases) tend to have their own collation schemes.

This is different from the ordering of the Japanese syllabary

Yes. Above and beyond collation issues in general, it's a massively difficult task to handle kanji accurately by syllable, because you have to guess at the pronunciation. JavaScript can't realistically know that by ‘藤本’ you mean ‘Fujimoto’ and not ‘touhon’; this sort of thing requires in-depth built-in dictionaries and still-unreliable heuristics... not the sort of thing you want to build in to a programming language.

Answer 6

You could implement the Unicode Collation Algorithm in Javascript if you want something better than the default JS sort for strings. Might improve some things. Though as the Unicode doc states:

Collation is not uniform; it varies according to language and culture: Germans, French and Swedes sort the same characters differently. It may also vary by specific application: even within the same language, dictionaries may sort differently than phonebooks or book indices. For non-alphabetic scripts such as East Asian ideographs, collation can be either phonetic or based on the appearance of the character.

The Wikipedia article points out that since collation is so tough in non-alphabetic scripts, now a days the answer is to make it very easy to look up information by entering characters, rather than by looking through a list.

I suggest that you talk to truly knowledgeable end users of your application to see how they would best like it to behave. The problem of ordering Chinese characters is not unique to your application.

Also, if you don't want to implement the collation in your system, another solution would for you to create a Ajax service that stores the names in a MySql or other database, then looks up the data with an order statement.

Answer 7

Others have answered the other questions, I will take on this one:

what should one strive for in creating a compare function for those languages?

One way to do it is that, you will need to create a program that can "read" the characters; that is, able to map hanzi/kanji characters to their "sound" (pinyin/hiragana reading). At the simplest level, this means a database that maps hanzi/kanji to sounds. Of course this is more difficult than it sounds (pun not intended), since a lot of characters can have different pronunciations in different contexts, and Chinese have many different dialects to consider.

Another way, is to order by stroke order. This means there would need to be a database that maps hanzi/kanji to their strokes. Another problem: Chinese and Japanese writes in different stroke orders. However, aside from Japanese and Chinese difference, using stroke ordering is much more consistent within a single text, since hanzi/kanji characters are almost always written using the same stroke order irrespective of what they meant or how they are read. A similar idea is to sort by radicals instead of plain stroke orders.

The third way, is sorting by Unicode code points. This is simple, and always gives undisputably consistent ordering; however, the problem is that the sort order is meaningless for human.

The last way is to rethink about the need for absolute ordering, and just use some heuristic to sort by relevance to the user's need. For example, in a shopping cart software, you can sort depending on user's buying habits or by price. This kinda avoids the problem, but most of the time it works (except if you're compiling a dictionary).

As you notice, the first two methods require creating a huge database of one-to-many mapping, but they still doesn't always give a useful result. The third method also require a huge database, but many programming languages already have this database built into the language. The last way is a bit of heuristic, probably most useful, however they are doomed to never give consistent ordering (much worse than the first two method).

Answer 8

The normal string comparison functions in many programming languages are designed to ensure that strings can be sorted into a unique order, to allow algorithms like binary search and duplicate-detection to work correctly. To sort data in a fashion meaningful to a human reader, one must know what the data represents. For example, in a list of English movie titles, "El Mariachi" would typically sort under "E", but in a list of Spanish movie titles it would sort under "M". The application will need information beyond that contained in the strings themselves to know how the strings should be sorted.

Answer 9

The answers to Q1 (can you sort) and Q3 (is sort meaningful) are both "yes" for Chinese (from a mainland perspective). For Q2 (how to sort):

All Chinese characters have definite pronunciation (some are polyphonic) as defined in pinyin, and it's far more common (as in virtually all Chinese dictionaries) to sort by pinyin, where there is no ambiguity. Characters with the same pronunciation are then sorted by stroke order.

The polyphonic characters pose extra challenge for sorting, as their pinyin usually depends on the word they are in (I heard Japanese characters could be even more hairy). For example, the character 阿 is pronounced a(1) in 阿姨 (tone in parenthesis), and e(1) in 阿胶. So if you need to sort words or sentences, you cannot simply look at one character at a time from each item.