Regular expressions ...

[Pimousse]

I'm definitively not a regexp expert !
Here's my problem.

I'm working on a string that looks like :
sin(1)+12.22-x2+x3+1/x4+1*17+56*ln(32+sin(26*x1))+exp(58)+1+ln(12)+sin(26)+pow(2,3)

etc etc ....

This string is built by an user, and I have to refactor it so that the
jvm could understand it.

x1 ... x5 are arguments which type is Double.

I already have some regexps that tranform ln to Math.log, sin to
Math.sin etc ... This is working perfectly, thanks to the help of some
guys from this forum

But as I'm working with java.lang.Math, I must use Double everywhere,
especially with fonction like pow() : indeed, if i do sth like pow(2,3),
java will throw me an exception (normal behaviour?).

So i must tranform all numbers like 2, 12558651 in 2.0 and 12558651.0.
But i mustn't changed 12.36 in 12.36.0, .45 in .45.0 or x1 in x1.0.

I made this regexp :

System.out.println("x1 : "+"x1".matches("(?<!\\.|x)[0-9]+[^\\.]"));
//--> false
System.out.println("12 : "+"12".matches("(?<!\\.|x)[0-9]+[^\\.]"));
//--> true
System.out.println(".12 : "+".12".matches("(?<!\\.|x)[0-9]+[^\\.]"));
//--> false
System.out.println("1245.12 :
"+"1245.12".matches("(?<!\\.|x)[0-9]+[^\\.]"));
//--> false

So I thought I had found the good regexp ! Actually not !
I'm using a code that looks like :

Pattern p = Pattern.compile(myPattern);
Matcher m = p.matcher(a);
StringBuffer buf = new StringBuffer(myChain);
int pos=0;
while(true){
if(m.find(pos)){
buf.insert(m.end()-1,".0");
pos = m.end()+m.group().length()-1;
System.err.println("i : "+(++i)+" - "+buf.toString());
System.err.println("I found the text \"" + m.group() +
"\" starting at index " + m.start() +
" and ending at index " + m.end() + " --> pos : "+pos);
m = p.matcher(buf.toString());
}
else{
a = buf.toString();
break;
}
}


The string I test is :
pow(2,3)+sin(1)+12.22-x2+x3+1/x4+1*17+56*ln(32+sin(26*x1))+exp(58)+1+ln(12)+sin(26)

Here's the result if I use the pattern (?<!\\.|x)[0-9]+[^\\.] :
pow(2.0,3.0)+sin(1.0)+1.02.22.0-x2+x3+1.0/x4+1.0*17.0+56.0*ln(32.0+sin(26.0*x1))+exp(58.0)+1.0+ln(12.0)+sin(26.0)
This pattern has a big problem with numbers like 78.69 or 1.8963 : it
transforms 12.22 in 1.02.22.0 !
But the remaining is "perfect".

If I use (?<!\\.|x)[0-9]+[^\\.0-9], here's the result :
pow(2.0,3.0)+sin(1.0)+12.22.0-x2+x3+1.0/x4+1.0*17.0+56.0*ln(32.0+sin(26.0*x1))+exp(58.0)+1.0+ln(12.0)+sin(26.0)
There's still a mistake as it changes 12.22 in 12.22.0 ....

Another pattern I tried was : \\b(?<!\\.|x)[0-9]+[^\\.0-9]\\b !
Here's the result :
pow(2.0,3)+sin(1)+12.22-x2+x3+1.0/x4+1.0*17.0+56.0*ln(32.0+sin(26.0*x1))+exp(58)+1.0+ln(12)+sin(26)
Here, there's no more problems with 12.22 but there are with integers ..

Can anyone helps me to point out my mistakes ?
Maybe I shouldn't use regexp ...
Tonight, I promise, I'll buy a book for mastering regexps on Amazon ...

 

[Roedy Green]

I'm working on a string that looks like :
sin(1)+12.22-x2+x3+1/x4+1*17+56*ln(32+sin(26*x1))+exp(58)+1+ln(12)+sin(26)+pow(2,3)

etc etc ....

what you want is a simple parser. Regexes are over their head for
this class of problem.

See http://mindprod.com/jgloss/parser.html

 

[Carl Howells]

Can anyone helps me to point out my mistakes ?
Maybe I shouldn't use regexp ...
Tonight, I promise, I'll buy a book for mastering regexps on Amazon ...

We have a winner!

This is NOT a particularly appropriate place to use a simple regex
package. You want a more sophisticated parser than a regex package can
supply. Look into something like javaCC for this. It should solve your
problems in a much simpler manner than creating giant regexes.

 

[Pimousse]

We have a winner!
so glad to be THE one !

This is NOT a particularly appropriate place to use a simple regex
package. You want a more sophisticated parser than a regex package
can supply. Look into something like javaCC for this. It should
solve your problems in a much simpler manner than creating giant
regexes.

Oh I solved it another way ....

Pattern p = Pattern.compile("\\b(?<!\\.)[0-9]+\\b");
Matcher m = p.matcher(myChain);
StringBuffer buf = new StringBuffer(myChain);
int pos=0;
while(true){
if(m.find(pos)){
buf.insert(m.start(),"(double)");
pos = m.end()+9;
m = p.matcher(buf);
}
else{
myChain = buf.toString();
m = null;
p = null;
buf = null;
break;
}
}
Indeed, 2.0 or (double)2 are the same ....

But you're right, i'm maybe not using the good method ...
But I only wanted to make the jvm understanding (hard to make to
computer understand sth ) I was using doubles and not integers !

Thanks for the idea of javaCC. the next, I'll use LEP ....

 

[TechBookReport]

We have a winner!

so glad to be THE one !

This is NOT a particularly appropriate place to use a simple regex
package. You want a more sophisticated parser than a regex package
can supply. Look into something like javaCC for this. It should
solve your problems in a much simpler manner than creating giant
regexes.

Oh I solved it another way ....

Pattern p = Pattern.compile("\\b(?<!\\.)[0-9]+\\b");
Matcher m = p.matcher(myChain);
StringBuffer buf = new StringBuffer(myChain);
int pos=0;
while(true){
if(m.find(pos)){
buf.insert(m.start(),"(double)");
pos = m.end()+9;
m = p.matcher(buf);
}
else{
myChain = buf.toString();
m = null;
p = null;
buf = null;
break;
}
}
Indeed, 2.0 or (double)2 are the same ....

But you're right, i'm maybe not using the good method ...
But I only wanted to make the jvm understanding (hard to make to
computer understand sth ) I was using doubles and not integers !

Thanks for the idea of javaCC. the next, I'll use LEP ....

Really, you need to take a look at JEP which does exactly what you need.
Take a quick trip to http://www.singularsys.com/jep/ and you'll be a
happier bunny...

Pan
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TechBookReport: http://www.techbookreport.com