Evaluate AND OR expression from a String in C#

mesharaasi

I am designing a rule engine in which the data resides in database in an expression format which is shown below. We are required to evaluate the expression in an order. If there is no "NOT" beside the option means we need to append "EQ" (equal). Since we need to execute in "AND","OR" order, we have to evaluate expression in the right format
EX:

Expression: NOT S:24zoll_1757 AND C:1757 AND C:1780
Conversion: (NOT S:24zoll_1757) AND (EQ C:1757) AND (EQ C:1780)

Expression: (S:gr1_1778 OR S:gr2_1778 OR S:gr5_1778)
Conversion: ((EQ S:gr1_1778) OR (EQ S:gr2_1778) OR (EQ S:gr5_1778))

#3:

Expression: S:25zoll_1757 AND S:ber7_1756
Conversion: (EQ S:25zoll_1757) AND (EQ S:ber7_1756)

#4:

Expression: S:25zoll_1757 AND NOT S:ber7_1756
Conversion: (EQ S:25zoll_1757) AND (NOT S:ber7_1756)

#5:

Expression: S:25zoll_1757 AND (NOT S:ber7_1756 OR S:ber8_1756)
Conversion: (EQ S:25zoll_1757) AND ( (NOT S:ber7_1756) OR (EQ S:ber8_1756) )

I have tried using Stack but it is working up to some extend. We have very complicated long statement which is not working.

Any ideas much appreciated?

5 Replies

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Muhammad Imran Ansari4y ago
Accepted answer
You can do this with string tokenization. below is the code which fullfill your all expressions. You can modify the logic if there is any other expression found. check below code:
public string ExpressionConversion(string expression)
{
    string finalVal = "";
    string currentToken = "";
    bool isNotFound = false;

    var values = expression.Split(new string[] { " " }, StringSplitOptions.None);
    for (int j = 0; j < values.Length; j++)
    {
        currentToken = values[j].Trim();

        if (currentToken.Contains("NOT"))
        {
            isNotFound = true;

            if (currentToken.StartsWith("("))
                finalVal += "((NOT ";
            else
                finalVal += "(NOT ";
            continue;
        }
        if (currentToken.StartsWith("AND"))
            finalVal += " AND ";
        else if (currentToken.StartsWith("OR"))
            finalVal += " OR ";
        else
        {
            if (isNotFound)
            {
                isNotFound = false;
                finalVal += currentToken + ")";
            }
            else
            {
                if (currentToken.StartsWith("("))
                    finalVal += "((EQ " + currentToken.Replace("(", "").Trim() + ")";
                else if (currentToken.EndsWith(")"))
                    finalVal += "(EQ " + currentToken.Replace(")", "").Trim() + "))";
                else
                    finalVal += "(EQ " + currentToken + ")";
            }
        }
    }
    return finalVal;
}
Calling:
ExpressionConversion("S:25zoll_1757 AND (NOT S:ber7_1756 OR S:ber8_1756)");
+2
mesharaasi4y ago
I have modified the code and it works well all scenarios

public static string ExpressionConversion(string expression)
{
string finalVal = "";
string currentToken = "";
bool isNotFound = false;
List strList = new List();
var values = CleverSplit(expression, ' ', false, true); //function which splits all the elements in the expression
for (int j = 0; j < values.Length; j++)
{
currentToken = values[j].Trim();
if (string.IsNullOrEmpty(currentToken.Trim()))
continue;
if ((j > 0) && currentToken.StartsWith("AND") && values[j - 1].StartsWith("AND"))
continue;
if (currentToken.Contains("NOT"))
{
isNotFound = true;
continue;
}
if (currentToken.StartsWith("("))
strList.Add(currentToken);
else if (currentToken.StartsWith(")"))
strList.Add(currentToken);
else if (currentToken.StartsWith("AND"))
strList.Add(" AND ");
else if (currentToken.StartsWith("OR"))
strList.Add(" OR ");
else
{
if (isNotFound)
{
strList.Add("( NOT " + currentToken + " )");
if (!expression.Contains("("))
isNotFound = false;
}
else
strList.Add("( EQ " + currentToken + " )");
}
}
if (strList.Count > 0)
finalVal = string.Join(" ", strList);
return finalVal;
}

+2
mesharaasi4y ago
I have resolved the issue but forgot to update here. Thank you so much for your help. Much appreciated.
+1
Muhammad Imran Ansari4y ago
Hi Mesharaasi,
I think this scenario we have resolved in your last post. These are the rules which we need to implement on the basis on any flag. I am sure, you have some values in your database which can differentiate the rule group. You can modify the code according to rule group and implement this expression.
+1
mesharaasi4y ago
Thank you so much for the code. This has eased most of my job now. I tried to change the logic for the following format but somehow it's not working.

Expression: NOT ((S:rad6_1755 OR S:rad66_1755 OR S:rad666_1755))
Output: (NOT S:rad6_1755) OR (NOT S:rad66_1755) OR (NOT S:rad666_1755)

Please help.
+1