Thread: Splitting text into several components

I'd work through the order of operations backwards. First, get rid of any spaces. Then, separate the String by its '+' and '-', so that all additive parts of the polynomial are separated. After that it should be easier to get at the coefficients (before the variable!) and exponents (after the caret!).

@Sean4u

That seems utterly and incredibly fascinating. I now go to read.

Thank you very much; I hadn't even heard of regular expressions until now!

well i'm back.

I tried to use the simple way, but honestly its not working out too well, fact is i dont even really have much to post on that i am trying to get the regex to work however, but i need some help. would it be something like:

import java.util.regex.Matcher;
import java.util.regex.Pattern;
 
 
public class test 
{
	public static void splitter(String s)
	{
			String str = "([0-9]{1,})x\\^([0-9]{1,})";
			Pattern p = Pattern.compile(str);
 
			Matcher matcher = p.matcher(s);
			boolean matchFound = matcher.find();
 
			if (matchFound) 
			{
 
			    for (int i=0; i<=matcher.groupCount(); i++) {
			        String groupStr = matcher.group(i);
			        System.out.println(groupStr);
			    }
			}			
 
	}			
 
 
	public static void main(String[] args) 
	{
		String s = "-12x^5+6x^3-3x+5";	
 
	splitter(s);
	}
 
}

is that correct?

I'm trying to run it but nothing is happening. no error or output. I am so confused...

Can anyone give me a hand please?

EDIT: Oh i figured it out how to get it to work with 1 term (12x^5), however it doesnt work with multiple terms (12x^5+3x^2)

One other thing, how can i get it to return negative values, such as -12x^5? It just returns 12,5 instead of -12,5

One other thing, how can i get it to return negative values, such as -12x^5? It just returns 12,5 instead of -12,5

I've been reading, and now I can help you with that! *cheesy superhero fanfare plays*

In a regex String, you can use the character ? to check if a certain character or character class occurs ONCE OR NOT AT ALL, such as in your - sign.

"([0-9]{1,})x\\^([0-9]{1,})"

This is what you currently have (I get it now, heehee!).

I think that you should amend it to be like this:

"(-?[0-9]{1,})x\\^(-?[0-9]{1,})"

Note that I'm not sure that this will work (I'm still reading the tutorial page as I post this xD). But it should, because it tells the matcher to check for a - before the numbers once, or not at all. Also note that instead of [0-9] you can just use \d, like this:

"(-?\\d{1,})x\\^(-?\\d{1,})"

It helps to read out what this regex is doing:

"Check for a negative sign occurring once or not at all, followed by any number of numbers, followed by "x^", followed by a negative sign occurring once or not at all, followed by any number of numbers."

This. Is. So. Cool.

Hmm... Well, if your polynomial terms are always going to be surrounded by spaces, you could use another regex, and the <String>.split(String regex) method:

Use this regex: "\s[+-]\s"

And the <String>.split(/*stick the regex here!*/) method, which will split the String at all the spots where that pattern occurs.

What it literally means is "split the String at a spot where there is a space, followed by a + or -, followed by a space".

Hopefully that will work...

And yes, I could see a Map working. You could also create your own Polynomial class, if you had other functions in mind, but if all you want is the coefficients and degrees, then a Map should be just fine.

EDIT: This is very interesting. I copied your test program, and with the parentheses, got this:

-12x^5
-12
5

But without them, got this:

-12x^5

I think it has to do with the groups created by the ( ). This is so interesting...

well this is strange...

I was starting to get desperate and frustrated since i've been working on this for about 8hours now, and i just kind of slammed by head against the keyboard then suddenly my code started working. lol but in all seriousness i found out how to get the regex thing to keep repeating.

Basically I changed:

if(matchFound)

to

while(matchFound)

then i appended this just outside the for loop BUT within the while loop:

matchFound = matcher.find(matcher.end());

I'm not sure if this is the proper way it's supposed to be done, but it works lol. I *think* what the code does is that it continues checking for a pattern right where it left off; not too sure to be honest as like i said i was just mashing away at the keyboard

i figured you might want to know.

I'm thinking about just passing all this stuff into a linkedhashmap with the exponents being teh key (the degrees are supposed to be unique), and then in turn passing the key/values into a bunch of nodes strung together to make polynomial. i think the linkedhashmap sorts stuff based on the key values. hopefully i'm able to retrieve key values...

this is my polynomial class:

class Polynomial
{
	Node head;	
 
	Polynomial()
	{
		head = new Node(null,null);
	}
 
	public void add(int coef, int power)
	{
		if(coef == 0)
		{
 
		}
		else
		{		
			Node temp = new Node(coef, power);
			Node current = head;
			// starting at the head node, crawl to the end of the list
			while(current.getNext() != null)
			{
				current = current.getNext();
			}
			// the last node's "next" reference set to our new node
			current.setNext(temp);
		}
	}
 
class Node<E>
	{
		E Element1, Element2;
		Node<E> next;
 
		public Node(E Element1,E Element2)
		{			
			this.Element1 = Element1;			
			this.Element2 = Element2;
			next = null;
		}
 
		public Node getNext()
		{
			return next;
		}
 
		public void setNext(Node next)
		{
			this.next = next;
		}
	}
}

What do you think?

Thank you so much for the help

i think the linkedhashmap sorts stuff based on the key values. hopefully i'm able to retrieve key values...

I found this (link for more detail):

get(Object key)
Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.

Hopefully that helps?

Also, I edited our regex again so that inputs like "3x" or "-6x" (that have no ^ and exponent) will still be accepted by the regex:

"-?\\d{1,}(x(\\^-?\\d{1,})?)?"

What I changed is red and bold. Basically it takes the "^[someNumber]" and puts the ONCE OR NOT AT ALL condition on it, stating that it can be there once, or not. Then, I did the same thing around the "x" part so that polynomials like "5" and "-3" work too! I tried it and it worked!

Thank you so much for the help

Thank you for posting! I think this is the most fun I've had learning Java... maybe ever!

Hahaha I'm gonna go to sleep for tonight, but I'll check out that code tomorrow! Good night!

Originally Posted by clydefrog

good night

thanks for the help. im gonna keep working on this

Seems like you're doing just fine. You're right - a reasonable pattern for something like you're doing could be (not tested by compiling)

Matcher matcher = PATTERN_POLY.matcher(inputString);
if (matcher.find())
{
  newPoly = new Poly();
  do
    newPoly.add(new Term(matcher.group(1), matcher.group(2)));
  while (matcher.find());
}
else
{ /* not a poly */ }

I like the idea of storing the terms by exponent in your class, that's neat. LinkedHashMap might not be quite right because it preserves the insertion order of its elements, and your input could be "4x^3+7x-x^2", right? TreeMap stores its entries sorted on natural order, but you can also provide your own Comparator.

Good luck with tuning your regular expression - that can be a labour of love! Would treating a term as (optional-sign)(optional-coefficient)x(optional-exponent) work? Don't forget to code for (or canonicalise) whitespace and case, and constant (x^0) terms!

I guess one über-simple option would be to implement your polynomial class as a Map of integer exponents onto signed integer coefficients, as opposed to having a separate class for the terms. The sorted map also makes reporting the 'degree' of your polynomial trivial.

Using this regex: "-?\d{1,}(x(\^-?\d{1,})?)?" (remember to add another \ before special characters)

And the input String: "-12x^-5+6x^3+3x-5", and only accepting group zero (the entire regex), I got this result:

-12x^-5
6x^3
3x
-5

So, the regex I'm using gets the right output and matches, but you'd have to do some extra fiddling with code outside of the regex to get the Polynomial values (which should be too hard). I'd just check to see if that match contains "x^" (in which case you could split the String at that point), and if not, check to see if the String has "x" (in which case the exponent is 1 and the coefficient is everything before x), and otherwise the exponent is 0 and the coefficient is the match. Hopefully that makes sense?

sweet! i did a quick test and it seems to work as you said. i'll be sure to implement that into my actual program.

However, i have another question. I know i'm beginning to leave the scope of this thread but i feel it would be better if i posted here since all the relevant info is already included in this thread.

Anyway, basically i've split my polynomials up into (coef,exp) and i've added it all into a treemap with the exponents being the key. Now the treemap has already sorted it out but i have a 2 part question:

1. it automatically sorts it in ascending order, (1, 2, 3...) but i need it in descending order (5, 4, 3, ...). How do i specify?

2. how can i actually get the key and values out of the treemap and stick into my constructor add(int coef, int exp)? I tried using an iterator, but iterator.keySet() and iterator.values() return objects, yet my constructor needs integers.

any ideas?

I remember you mentioned something about using a comparator to avoid the map, how would i go about doing that? Is there a way i can just go and reorder my nodes based on the exponent? My nodes contain 2 elements (coef, exp) and multiple nodes strung together forms a polynomial.

If you need to get a better idea here is my basic code:

class Polynomial
{
	Node head;	
 
	Polynomial()
	{
		head = new Node(null,null);
	}
 
	public void add(int coef, int power)
	{
 
		Node temp = new Node(coef, power);
		Node current = head;
		// starting at the head node, crawl to the end of the list
		while(current.getNext() != null)
		{
			current = current.getNext();
		}
		// the last node's "next" reference set to our new node
		current.setNext(temp);
 
class Node<E>
	{
		E Element1, Element2;
		Node<E> next;
 
		public Node(E Element1,E Element2)
		{			
			this.Element1 = Element1;			
			this.Element2 = Element2;
			next = null;
		}
 
		public Node getNext()
		{
			return next;
		}
 
		public void setNext(Node next)
		{
			this.next = next;
		}
	}
}
 
	}

it automatically sorts it in ascending order, (1, 2, 3...) but i need it in descending order (5, 4, 3, ...). How do i specify?

I've never worked with TreeMap before, but would it be possible for you to move through the keys backwards?

how can i actually get the key and values out of the treemap and stick into my constructor add(int coef, int exp)? I tried using an iterator, but iterator.keySet() and iterator.values() return objects, yet my constructor needs integers.

You can class cast objects to other objects; so, as long as the inputs to your TreeMap are of the class Integer, you can class cast the objects returned by the iterator to Integers, and the use the intValue() method.

Class casting works like this:

Object cake = new Integer(); //Integer is a subclass of Object (like everything)
 
Integer cakeInteger = (Integer)cake; //cake can be cast to an Integer (that's what we initialized it as)

You're welcome! So, I'm curious, what is the extent of this program's functionality? How much and what will it do when it's done?