Get variable names from expression about parsii HOT 12 CLOSED

I just pushed a commit which added a getNames() method to Scope. So you could do something like:

    Scope s = Scope.create();
    Parser.parse("a*b+c", s);
    s.getName(); // Will contain all referenced variables

Note that I didn't update the maven release yet, but that wouldn't be a problem if required...

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Cool just what I wanted, can you update the Maven repo, cause it just happens I'm using Maven, and would not want to add it to my nexus repo.

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Also for convienance I think it would be conveniant for the Expr to have a function returning the scope, for places where the expression parsing and evaluation is done in different classes. Now you would need to store both expr and scope, and recall both at usage time.

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Technically the scope is only used when parsing expressions. That's the place where variable names are resolved into Variable instances. Accessing a variable later on is as cheap as a field access - no more lookups are performed. This is one reason for parsii being quite fast. If you still need / want those two tied together, you could create class "Computation" or the like with two fields "expression" and "scope". That should probably do the trick?

I just released parsii-1.2 (should take about one day to be mirrored into the main repo).

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I see. So for the following use case: let there be a user provided arbitrary expression, such as "a+b" (but may as well be x+y).

To make the calculation my initial impluse is:

 s = Scope.create()
 expr = Expr.parse(stringExpresion, s);

much later on, in different class, expr and scope passed as reference:

 names=s.getNames()
 for i=1:100000
   for name in names: 
         s.getVariable(name).setValue(get(i, name))
   res[i] = expr.evaluate()

Let us assume that get always returns some value. If I understand correctly what you say is that evaluate always returns the expression with the scope variables at parse time? (meaning that I would need to reparse the expression again and again) Am I right?

Furthermore, I could of course write myself an enclosing class, but I have its place would be right inside the parsii.

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Almost - you don't need to reparse the expression and expr doesn't have a setVariable method. The code would roughly look like this:
names=s.getNames()
for i=1:10
for name:names:
Variable v = s.find(name);
v.setValue(get(i, name));
res[i] = expr.evaluate();

We could make this way more performant by providing a Scope.getVariables() method which directly returns all known variables:
for i = 1..10:
for v : s.getVariables():
v.setValue(get(i, v.getName()));
res[i] = expr.evaluate();

This way, no lookups are performed in the inner loop. Would that work for you?

from parsii.

That would be excelent. :)

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I just added such a method - A snapshot is available as: parsii-1.3-20140514.161553-1.jar or 1.3-SNAPSHOT should also resolve to this revision. This might also take some hour to be mirrored...

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So I'like now how it works, but is it neccessary to return pi and euler as these are constants?
I mean for now I would not to write an if to escape them... and all my code would certainly break if later on we introduce another constant. But the extra ifs alone would make akward to use it. Maybe we should add a getNonConstantVariableNames() function where to escape these? Any ideas for these?

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I added a getter: getLocalVariables - this will exclude all global constants (as those would reside in the global root context). A maven snapshot is available...

Another sexy approach would have been using java 8: scope.getVariables().stream().filter(v -> !v.isConstant()).forEach(.....) ;-)

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I cannot see the snapshot mirrored (http://mvnrepository.com/artifact/com.scireum/parsii), any ideas why?

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As far as I'm aware of, you need to add the snapshot repository of sonatype
to your list of repos:
https://oss.sonatype.org/content/repositories/snapshots (Sorry I'm by no
means a maven expert).

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2014-05-22 10:19 GMT+02:00 Gábor Bernát [email protected]:

I cannot see the snapshot mirrored (
http://mvnrepository.com/artifact/com.scireum/parsii), any ideas why?

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Reply to this email directly or view it on GitHubhttps://github.com//issues/2#issuecomment-43860292
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