dportabella
asked on
regular expressions in Java
I have the following function:
String transform(String input) {
Pattern pattern = Pattern.compile("(\d+) (Jan|Feb|Mar) (\d\d\d\d)");
Matcher matcher = pattern.matcher(input);
return matcher.replaceAll("$3 $2 $1");
}
transform("3 Feb 1987") returns "1987 Feb 3"
That's ok.
How could I modify the transform function, so that
transform("3 Feb 1987") returns "1987 02 3"
?
I know that I could achieve it by adding extra java code,
so that it gets the month string, and then transform it into a number using a simple hashmap, for instance.
However, I would like to achieve this without adding any extra java code, just by modifying only the Pattern.compile and matcher.replaceAll instructions.
Is this possible? Maybe with another regular expression package?
I am thinking something such as the following:
Pattern pattern = Pattern.compile("(\d+) (Jan=01|Feb=02|Mar=03) (\d\d\d\d)");
Matcher matcher = pattern.matcher(input);
return matcher.replaceAll("$3 $2 $1");
Do you know how to achieve this?
-----
ps: This is just an example for me to understand; I know that I could achieve it by using the Date formating and parsing functions of Java (so, without using regular expressions)
String transform(String input) {
Pattern pattern = Pattern.compile("(\d+) (Jan|Feb|Mar) (\d\d\d\d)");
Matcher matcher = pattern.matcher(input);
return matcher.replaceAll("$3 $2 $1");
}
transform("3 Feb 1987") returns "1987 Feb 3"
That's ok.
How could I modify the transform function, so that
transform("3 Feb 1987") returns "1987 02 3"
?
I know that I could achieve it by adding extra java code,
so that it gets the month string, and then transform it into a number using a simple hashmap, for instance.
However, I would like to achieve this without adding any extra java code, just by modifying only the Pattern.compile and matcher.replaceAll instructions.
Is this possible? Maybe with another regular expression package?
I am thinking something such as the following:
Pattern pattern = Pattern.compile("(\d+) (Jan=01|Feb=02|Mar=03) (\d\d\d\d)");
Matcher matcher = pattern.matcher(input);
return matcher.replaceAll("$3 $2 $1");
Do you know how to achieve this?
-----
ps: This is just an example for me to understand; I know that I could achieve it by using the Date formating and parsing functions of Java (so, without using regular expressions)
Is there a reason you need to do this using regular expression? I think it might be easier to achieve this throug SimpleDateFormat:
DateFormat input = new SimpleDateFormat("d MMM yyyy", Locale.US);
DateFormat outputOne = new SimpleDateFormat("yyyy MMM d", Locale.US);
DateFormat outputTwo = new SimpleDateFormat("yyyy MM d", Locale.US);
Date date = input.parse("3 Feb 1987");
System.out.println(outputO
System.out.println(outputT
DateFormat input = new SimpleDateFormat("d MMM yyyy", Locale.US);
DateFormat outputOne = new SimpleDateFormat("yyyy MMM d", Locale.US);
DateFormat outputTwo = new SimpleDateFormat("yyyy MM d", Locale.US);
Date date = input.parse("3 Feb 1987");
System.out.println(outputO
System.out.println(outputT
ASKER
kralikX,
Maybe it is not possible using the regexp package from java.
What about other regular expression packages?
What about using a transducer package?
I really would like to have something like this:
Pattern pattern = Pattern.compile("(\d+) (Jan=01|Feb=02|Mar=03) (\d\d\d\d)");
Matcher matcher = pattern.matcher(input);
return matcher.replaceAll("$3 $2 $1");
Bart_Cr,
As I said, that was just an example to learn about parsers/transducers in java.
Maybe it is not possible using the regexp package from java.
What about other regular expression packages?
What about using a transducer package?
I really would like to have something like this:
Pattern pattern = Pattern.compile("(\d+) (Jan=01|Feb=02|Mar=03) (\d\d\d\d)");
Matcher matcher = pattern.matcher(input);
return matcher.replaceAll("$3 $2 $1");
Bart_Cr,
As I said, that was just an example to learn about parsers/transducers in java.
You can't do that with a regex alone - you need a lookup table. Of course the proper way to do it is shown by Bart_Cr
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I found something called Java Transducer Interface (JTI) but it is aimed to work with hardware sensors, etc.
ASKER
Hello kralikX,
>.. it should be possible to extend regexp language in similar manner as you suggest
>(I'd choose syntax that would be easily parseable using regexp again) and preprocess it in your code.
Hey, I like that idea!
However, I would like to be sure that somebody else has not already done so, before going for it.
Of course, I would prefer that somebody had already done it, and to know about it :)
About a transducer package for java, I just found this project:
http://sourceforge.net/projects/esw/
However, the website about the SimpleTransduction example is not working:
http://esw.sourceforge.net/nodeandmetacollectionsexamples.html
>.. it should be possible to extend regexp language in similar manner as you suggest
>(I'd choose syntax that would be easily parseable using regexp again) and preprocess it in your code.
Hey, I like that idea!
However, I would like to be sure that somebody else has not already done so, before going for it.
Of course, I would prefer that somebody had already done it, and to know about it :)
About a transducer package for java, I just found this project:
http://sourceforge.net/projects/esw/
However, the website about the SimpleTransduction example is not working:
http://esw.sourceforge.net/nodeandmetacollectionsexamples.html
> Of course, I would prefer that somebody had already done it, and to know about it :)
I understand that :-).
Thanks for the link to ESW, seems quite interesting.
I understand that :-).
Thanks for the link to ESW, seems quite interesting.
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:-)
I don't think it is achievable modyfying only regexp and replacement pattern in your code. If you don't want to program specific logic for some concrete replacement (like Jan -> 01, etc. in your example), I guess the simplest you could do with is to match a set of regexps and patterns. Then you would pass separate regexp and replacement for each month.
KralikX.