Extract Mel Command And Math Operator From String

[huasen]

Hi,

I have simple question to ask. I have a string that consist of mel commands and also mathematical operators.

Can somebody tell me how to extract out these commands and math operators and discard them ?

For example:

$stringEx =" clamp(0,1, clamp(0,1, $someInt+1)*$someInt2)";

What I want as an output is:
(0,1,
(0,1, $someInt
1)
$someInt2)

Thanks

[failure]

why?

[huasen]

Its just a sample string

[failure]

Your question is not clear - describe what is that you want to do and why.
Mel can do regular expressions which is a standard way to do various string search/replacement operations. The command is: substitute.

[joojaa]

failure is right, its better to fix your apprach than tell yiou synbtax it generates better code for you. Se even if you think the approach youve taken is the best it might not. So you could get MUCH more valauble advice by explaining your ENTIRE intent. Sure we can aswer your suntactoic question but you should consult the commad reference yoruslef realy (because me showing it wont meka you more able to slove general problems like this).

also your description is not clear:

$stringEx =" clamp(0,1, clamp(0,1, $someInt+1)*$someInt2)";

What I want as an output is:

$stringEx =" clamp(0,1, clamp(0,1, $someInt+1)*$someInt2)";

What I want as an output is:
(0,1,
(0,1, $someInt
1)
$someInt2)

does that mean thet the entters are menaingfull or is each line a a array menber or what?

PS please note maya 7 now has a new form of substitute not mentioned in teh command reference! Its using 2 argumenst instead of 3 heres a example

CODE
{
 $allOperators={"clamp","\*","\+"}; //note quoting * and  +as its a special regex term
 $stringEx =" clamp(0,1, clamp(0,1, $someInt+1)*$someInt2)";
 for ($operation in $allOperators)
   $stringEx=substitute $stringEx ("s/"+$operation+"/\n/g"); // maya 7 only!
 print $stringEx;
}

[failure]

Looks like he wants to tokenize a string

[joojaa]

Yes but he does not SAY SO! thats why i calrifed that his decription is not sane. Presumably tough hes xporting it to a file so ho realy woudl like them on separate lines so he can dump it into a file... maybe what would i know.

BUt if hes trying to amke a script teht turns arithmetics into nodes then hes not necceserily on the optimal path.

[failure]

Oh, he's trying to make an expression parser. Well that's not trivial. Definitely a job for python.

[joojaa]

Yes but why would one want to, unless the prurpose is to build node networks, otherwise theres no idea in it whatsoever. ITs like the one guy who posted a per frame per particle evalling melscript because he didnt know off particle expressions.*

because:

1. maya has a expression parser so you can jsut use that.
2. if ist going into a external application then why not parese it externaly.

*this brings us to another topic entirely where its not usefull to start scripting thinhgs untill youve explored quite thoroughly what maya offers and keep a lookout for any new tricls.

[huasen]

Hi all

Thanks for your input. I was on sick leave yesterday, so I didn't check the forum. Sorry about that.

What I want to do is like what Joojaa said. I want to automatically create a network of nodes given an expression. My idea is to tokenize the expression and extract the operator, command and value from there.

It might not be the best idea anyway. So I'm open for any ideas on how to do it more efficiently.

Thanks again guys...

[failure]

Althoug it looks seductive at first, this thing would actually be useless and it's just not worth the efffort.
Normally if you want to parse na expression it's not enough just to tokenize, you need to build a tree data structure containig operators ( functions ) and operands. Then you traverse the structure and evaluate as you go - or in your case - build a dg. Tree is needed because of generally recursive nature of expressions - operators become operands etc. For example, expression like this ( operators are written as functions for clarity):

add( 10, multiply( 2, 30 ) )

would translate into tree:

CODE
add
/   \
10  mul
    /  \
   2   30

You need to take care about operator precedence when parsing or let the input expression syntax explicitely demand usage of parenthesis or represent all operators as functions. Which leads to anoher not-trivial problem to solve - syntax checking. What type of identifiers are allowed, what type of literals ( string, floating point, vector etc.. ), number of arguments for each operation, which node atributes are represented by operands? All this need to be handled by parser.
Anyway today noone would bothers writing a parser since we have dozens of general purpose parsing tools and apis.

Since expresions are trees and dg is a lattice graph ( a superset of tree structure ) - not every connection set could be represented by a tree, plus connections could be made to different attributes while expression operators assume implicite role of each operand. Again, this couldn't be translated sucessfuly. Unless you of course treat nodes as data structures which would effectively mean - reinventing the mel itself.

[joojaa]

I do quite distinictly remeber this mel is allready written and you can download it for further expanion for yoru needs form higehend.

easiest is if you can just asume everything is perfectly ordered inside parentheses.

I suggest you use tokenize instead of substitute loops when you use singyular delimitters its faster. if you msut use this approach.

then you can allways take the first part up to the parenthesis create that node, read in the datas of such nodes and populate them wich each node that comes along)

NOW one thing to note! a expression is not NECCESERILY slower than the equal thing expressed as a node network. IT greatly depends on what is connected and how those connections change. let use consider the following network. IT may in some instances be substantialy faster.

IM asuming here you use pure expressions not something that uses mel inside, jiust direct connections and pure expressivity

CODE
   CLAMP
   /  |  \
 1    0  ADD
          /   \
         1    MULT
              /     \
             0.5    Some input connection

NOw then this routine is NOT simplified by a node network one bit, infact it may be thet teh expression is more efficient in this case, oratleast a similliar case where there are more operations. Because all teh nodes need to be evaluated anyway, but they arenent evaluated in one go wich is the case for expressions, the expression eingene is possibly more efficient here (or atleast it will be once teh chain gets bigger).

Likewise if all or most the input connections downstream have tendency to change from eval to eval, then it does not matter that there are several inputs. However if teh ibnputs change frequantly indoependently freom eachoter its a different thing. (note it can be true that network is slightly faster for animation but NOT playback wich is more critical anyway)

however:

CODE
        ADD
       /      \
   CLAMP  Input connection that changes OFTEN
   /  |  \
 1    0  ADD
          /   \
             MULT
              /     \
             0.5    Some input connection thet rarely changes

NOW this may infact be faster because the values of the entire CLAMP subtree is cached. NOW however you could compress the lower part to a expression isntead

CODE
        ADD
       /      \
     EXPR   Input connection that changes OFTEN
        |  
   Some input connection thet rarely changes

Something to thinkabout.

[failure]

Note that I use term "expression" in a general sense, not as maya animation expression.
Anyway there is no much benefit in truning simple algebraic-like expressions into node networks since maya expressions serve the purpose of evaluating these constructs- something that joojaa pointed out already.
On the other side a general type parser that could convert something like:

parent( transform( locatorShape ), transform( mesh( polyCube ) + mesh( polySphere ) ) )

would just be too much trouble to write in respect to number of node types and number of possible (useful) connections. And it wouldnt be much more effective than createNode / connectAttr