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How to convert a search string to a boolean condition?

I have a search criteria stored in a string:
string Searchstr = "(r.Value.Contains("PwC") || (r.Value.Contains("Canadian") && r.Value.Contains("thrive"))) || (r.Value.Contains("Banana") && r.Value.Contains("Gayle"))"
I want to use this in a If statement to check the values:
if(searchstr)
{
then do this....
}
but the if should have a searchstr as boolean.
How to convert this to boolean?
EDIT: The requirement is to give search criteria dynamically in a text box in the following format - "PwC OR (Canadian AND thrive)".
Which will be used to search an XML file.
Therefore I have loaded an XML file and want to have a Where condition in LINQ for which I need to use Dynamic LINQ but string is not allowed in that and also I have some braces to deal with.
Thinking of that I have taken the resultset from the XML(The tag value which i need to search)
var selectedBook = from r in document.Root.Descendants("Archives").Elements("Headline").Elements("Para")
select r;
and would ideally like to try something like:
var query=selectedbook.Where(searchstr)
OR
if(searchstr){....then do this}

You will need to do a bit of work to make this happen, but it is possible.
You should have a look at the dynamic LINQ library. This allows you to specify LINQ conditions (and other clauses) as strings and execute them just like LINQ operators.
Start with the explanation on ScottGu's blog and follow the links:
http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx

I'm assuming the string is going to reference only a specific set of objects (r or r.Value in this case, for example - or anything else you want, as long as you know it beforehand). If this is the case, then:
Create a delegate that takes the objects (that may be referenced) as parameters
and returns a bool, as you want.
Programmatically write a small C# source file in memory that defines the query
as the body of a method (with a fixed name, preferably) that conforms to the delegate specified above.
Use the CSharpCodeProvider class to compile an assembly
with your custom function that returns the bool you want.
Run the dynamically written and compiled code from your main program.

Well as you may guess it is not going to be straight forward but at the same time it is not as hard a problem as it seems
You can perform a few steps to get what you want:
Get the search expression as input (for e.g. "PwC OR (Canadian AND thrive)")
Write an extension method on XElement that returns true and takes the search criteria as input. You will then be able to use
var selectedBook = from r in
document.Root.Descendants("Archives").Elements("Headline").Elements("Para")
where r.SatisfiesCriteria(searchCriteria)
select r;
Write a parser class that parses searchCritera and stores it in parsed format. (for e.g. you can convert it into postfix notation). This is quite easy and you can use standard algorithm for this. For your purpose OR, AND will be operators and PwC etc. will be operands. Parenthesis will get removed as part of parsing.
Now simply invoke this parser from with in your extension method and then evaluate the postfix expression you get. This again can be done through standard stack based evaluation. Infact it would be better if you parse the criteria once and then only evaluate in where. While evaluating you need to replace the operands with r.Value.Contains

It seems like a good scenario for http://scriptcs.net/

is there any method that will find nearest match

I want to compare two strings, such as:
str1 = "this is a dynamic data";
str2 = "this is a <data_1> data";
Is there any method that will find the nearest match? I have used Ternary Search Tree (TST) Dictionary functions. Are there any other ways to do this kind of thing?

What about the Jaccard similarity coefficient?
http://en.wikipedia.org/wiki/Jaccard_index
It's easy to implement and gives a good similarity score. You have to tokenize your sentences though ;)

There is no such method in BCL that finds nearest match of the string.
But you can roll your own.
read about "Levenshtein Distance" on the following link

In am not sure about this thing in C#, but yes that is there in SQL,
select difference('this is a dynamic data','this is a dynamic')

RegEx replace with calculations?

Is it possible somehow to do a RegEx-replace with a calculation in the result? (in VS2010)
Such as:
Grid\.Row\=\"{[0-9]+}\"
to
Grid.Row="eval(int(\1) + 1)"

You can use a MatchEvaluator do achieve this, like
String s = Regex.Replace("1239", #"\d", m => (Int32.Parse(m.ToString()) + 1).ToString());
Output: 23410
Edit:
I just noticed... if you mean "using the VS2010 find-replace feature" and not "using C#", then the answer is "no", i am afraid.

You could always use capturing to retrieve any values you need for your calculation and then perform a RegEx Replace with a new RegEx that's constructed from you're equation and any values you captured.
If the equation doesn't use anything from the input text, one RegEx would be sufficient. You'd simply construct it by concatenating the static portions together with the computed value(s).

Unfortunately, C# and .NET do not provide an eval method or equivalent. However, it is possible to either use a library for expression parsing (a quick google gave me this .NET Math Expression Parser) or write your own (which is actually pretty easy, check out the Shunting-yard Algorithm and Postfix Notation). Simply capture the group then output the group value to the library/method you have written.
Edit: I see now you want this for the VS2010 program. This is unachievable unless you write your own VS extension. You could always write a program to search and replace your code and feed the code into it, then replace it the original code with its output.

how to create a parser for search queries

for example i'd need to create something like google search query parser to parse such expressions as:
flying hiking or swiming
-"**walking in boots **" **author:**hamish **author:**reid
or
house in new york priced over
$500000 with a swimming pool
how would i even go about start building something like it? any good resources?
c# relevant, please (if possible)
edit: this is something that i should somehow be able to translate to a sql query

How many keywords do you have (like 'or', 'in', 'priced over', 'with a')? If you only have a couple of them I'd suggest going with simple string processing (regexes) too.
But if you have more than that you might want to look into implementing a real parser for those search expressions. Irony.net might help you with that (I found it extremely easy to use as you can express your grammar in a near bnf-form directly in code).

The Lucene/NLucene project have functionality for boolean queries and some other query formats as well. I don't know about the possibilities to add own extensions like author in your case, but it might be worthwile to check it out.

There are few ways doing it, two of them:
Parsing using grammar (useful for complex language)
Parsing using regular expression and basic string manipulations (for simpler language)
According to your example, the language is very basic so splitting the string according to keyword can be the best solution.
string sentence = "house in new york priced over $500000 with a swimming pool";
string[] values = sentence.Split(new []{" in ", " priced over ", " with a "},
StringSplitOptions.None);
string type = values[0];
string area = values[1];
string price = values[2];
string accessories = values[3];
However, some issues that may arise are: how to verify if the sentence stands in the expected form? What happens if some of the keywords can appear as part of the values?
If this is the case you encounter there are some libraries you can use to parse input using a defined grammar. Two of these libraries that works with .Net are ANTLR and Gold Parser, both are free. The main challenge is defining the grammar.

A grammar would work very well for the second example you gave but the first (any order keyword/command strings) would be best handled using Split() and a class to handle the various keywords and commands. You will have to do initial processing to handle quoted regions before the split (for example replacing spaces within quoted regions with a rare/unused character).
The ":" commands are easy to find and pull out of the search string for processing after the split is completed. Simply traverse the array looking.
The +/- keywords are also easy to find and add to the sql query as AND/AND NOT clauses.
The only place you might run into issues is with the "or" since you'll have to define how it is handled. What if there are multiple "or"s? But the order of keywords in the array is the same as in the query so that won't be an issue.

i think you should just do some string processing. There is no smart way of doing this.
So replace "OR" with your own or operator (e.g. ||). As far as i know there is no library for this.
I suggest you go with regexes.

How can I build a Truth Table Generator?

I'm looking to write a Truth Table Generator as a personal project.
There are several web-based online ones here and here.
(Example screenshot of an existing Truth Table Generator)
I have the following questions:
How should I go about parsing expressions like: ((P => Q) & (Q => R)) => (P => R)
Should I use a parser generator like ANTLr or YACC, or use straight regular expressions?
Once I have the expression parsed, how should I go about generating the truth table? Each section of the expression needs to be divided up into its smallest components and re-built from the left side of the table to the right. How would I evaluate something like that?
Can anyone provide me with tips concerning the parsing of these arbitrary expressions and eventually evaluating the parsed expression?

This sounds like a great personal project. You'll learn a lot about how the basic parts of a compiler work. I would skip trying to use a parser generator; if this is for your own edification, you'll learn more by doing it all from scratch.
The way such systems work is a formalization of how we understand natural languages. If I give you a sentence: "The dog, Rover, ate his food.", the first thing you do is break it up into words and punctuation. "The", "SPACE", "dog", "COMMA", "SPACE", "Rover", ... That's "tokenizing" or "lexing".
The next thing you do is analyze the token stream to see if the sentence is grammatical. The grammar of English is extremely complicated, but this sentence is pretty straightforward. SUBJECT-APPOSITIVE-VERB-OBJECT. This is "parsing".
Once you know that the sentence is grammatical, you can then analyze the sentence to actually get meaning out of it. For instance, you can see that there are three parts of this sentence -- the subject, the appositive, and the "his" in the object -- that all refer to the same entity, namely, the dog. You can figure out that the dog is the thing doing the eating, and the food is the thing being eaten. This is the semantic analysis phase.
Compilers then have a fourth phase that humans do not, which is they generate code that represents the actions described in the language.
So, do all that. Start by defining what the tokens of your language are, define a base class Token and a bunch of derived classes for each. (IdentifierToken, OrToken, AndToken, ImpliesToken, RightParenToken...). Then write a method that takes a string and returns an IEnumerable'. That's your lexer.
Second, figure out what the grammar of your language is, and write a recursive descent parser that breaks up an IEnumerable into an abstract syntax tree that represents grammatical entities in your language.
Then write an analyzer that looks at that tree and figures stuff out, like "how many distinct free variables do I have?"
Then write a code generator that spits out the code necessary to evaluate the truth tables. Spitting IL seems like overkill, but if you wanted to be really buff, you could. It might be easier to let the expression tree library do that for you; you can transform your parse tree into an expression tree, and then turn the expression tree into a delegate, and evaluate the delegate.
Good luck!

I think a parser generator is an overkill. You could use the idea of converting an expression to postfix and evaluating postfix expressions (or directly building an expression tree out of the infix expression and using that to generate the truth table) to solve this problem.

As Mehrdad mentions you should be able to hand roll the parsing in the same time as it would take to learn the syntax of a lexer/parser. The end result you want is some Abstract Syntax Tree (AST) of the expression you have been given.
You then need to build some input generator that creates the input combinations for the symbols defined in the expression.
Then iterate across the input set, generating the results for each input combo, given the rules (AST) you parsed in the first step.
How I would do it:
I could imagine using lambda functions to express the AST/rules as you parse the tree, and building a symbol table as you parse, you then could build the input set, parsing the symbol table to the lambda expression tree, to calculate the results.

If your goal is processing boolean expressions, a parser generator and all the machinery that go with is a waste of time, unless you want to learn how they work (then any of them would be fine).
But it is easy to build a recursive-descent parser by hand for boolean expressions, that computes and returns the results of "evaluating" the expression. Such a parser could be used on a first pass to determine the number of unique variables, where "evaluation" means "couunt 1 for each new variable name".
Writing a generator to produce all possible truth values for N variables is trivial; for each set of values, simply call the parser again and use it to evaluate the expression, where evaluate means "combine the values of the subexpressions according to the operator".
You need a grammar:
formula = disjunction ;
disjunction = conjunction
| disjunction "or" conjunction ;
conjunction = term
| conjunction "and" term ;
term = variable
| "not" term
| "(" formula ")" ;
Yours can be more complicated, but for boolean expressions it can't be that much more complicated.
For each grammar rule, write 1 subroutine that uses a global "scan" index into the string being parsed:
int disjunction()
// returns "-1"==> "not a disjunction"
// in mode 1:
// returns "0" if disjunction is false
// return "1" if disjunction is true
{ skipblanks(); // advance scan past blanks (duh)
temp1=conjunction();
if (temp1==-1) return -1; // syntax error
while (true)
{ skipblanks();
if (matchinput("or")==false) return temp1;
temp2= conjunction();
if (temp2==-1) return temp1;
temp1=temp1 or temp2;
}
end
int term()
{ skipblanks();
if (inputmatchesvariablename())
{ variablename = getvariablenamefrominput();
if unique(variablename) then += numberofvariables;
return lookupvariablename(variablename); // get truthtable value for name
}
...
}
Each of your parse routines will be about this complicated. Seriously.

You can get source code of pyttgen program at http://code.google.com/p/pyttgen/source/browse/#hg/src It generates truth tables for logical expressions. Code based on ply library, so its very simple :)