add string between strings if they are not null or empty

Question

Supossing I have 4 strings I want to add an OR operator between them:

Dim s1="db = 45 AND frec = 500 "
Dim s2="db = 25 AND frec = 1 "
Dim s3="db = 5 AND frec = 2 "
Dim s4="db = 15 AND frec = 4 "

so

Dim result = "db = 45 AND frec = 500 OR db = 25 AND frec = 1 OR db = 5 AND frec = 2 OR db = 15 AND frec = 4"

Thw woul be easy as concatenating strings

Dim result= s1 & " OR " & s2 & " OR " & s3 & " OR " & s4

However in general, any of strings could be empty or be null so if I concatenate empty strings I would get

For instance s2 = ""

Dim result = "db = 45 AND frec = 500 OR  OR db = 5 AND frec = 2 OR db = 15 AND frec = 4"

which is incorrect, I was thinking to replace strings like "OR OR"

 Dim result = result.Replace("OR OR", "")

Is there a better approach? a quick solution would be to hard code all cases but guess that is not so good

(I cannot change the design of this, as the strings are used on several other things)

answers are good enough for your answer, but i would totally follow a different design such as using nodes and graphs. — DarthVader
– DarthVader, Commented Aug 19, 2013 at 20:04
Just check for IsNullOrEmpty prior to concatenating each one. It won't all be on one line, but that doesn't matter. — cwhelms
– cwhelms, Commented Aug 19, 2013 at 20:05

sehe · Accepted Answer · 2013-08-19 20:02:52Z

6

In C#:

 string.Join(" OR ", new[] { stringA, stringB }
      .Where(s => !string.IsNullOrEmpty(s)));

Note that this will work with larger arrays too. Add .ToArray() in case you're on .NET <4.0

answered Aug 19, 2013 at 20:02

sehe

401k49 gold badges475 silver badges673 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

edgarmtze Over a year ago

Would a trasnlation to vb be String.Join(" OR ", New (){stringA, stringB}.Where(Function(s) Not String.IsNullOrEmpty(s))).ToArray() ?? I am using .NET 2

sehe Over a year ago

@cMinor Move the .ToArray inside the parens: String.Join(" OR ", New (String.Empty){stringA, stringB}.Where(Function(s) Not String.IsNullOrEmpty(s)).ToArray()) (you want to affect the String[] array parameter to String.Join

John Tabernik · Accepted Answer · 2013-08-19 20:15:47Z

0

I just want to throw something out in case you are planning to execute this against a database or something along those lines. Simply putting an "OR" between the clauses is not going to return the results you expect. You need to put parenthesis around the conditions first to preserve the logic as you have it.

Most like you mean something like:

(db = 45 AND frec = 500) OR (db = 25 AND frec = 1) OR (....

Just be careful, or you may be surprised by what you get back. Good luck!

answered Aug 19, 2013 at 20:15

John Tabernik

3523 silver badges12 bronze badges

5 Comments

Jacob Krall Over a year ago

AND has higher precedence than OR, so your example is exactly equal to db = 45 AND frec = 500 OR db = 25 AND frec = 1 OR ....

John Tabernik Over a year ago

@jacob-krall That is true for evaluating logic in C# for example, but that is false for SQL syntax. Try running a query against SQL Server and check the results, or search the web (the first article I found on it was here.

Jacob Krall Over a year ago

the article you linked very clearly shows that OR has lower precedence than AND. That is why they had to put parentheses around the OR clause.

Jacob Krall Over a year ago

Here is the TechNet documentation: technet.microsoft.com/en-us/library/ms190276.aspx

John Tabernik Over a year ago

@jacob-krall I stand corrected!! I have seen issues in the past with this and have always included parenthesis--I must have not been paying attention to the AND/OR order of precendence. Thanks for pointing this out!

Collectives™ on Stack Overflow

add string between strings if they are not null or empty

2 Answers 2

2 Comments

5 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

5 Comments

Your Answer

Sign up or log in

Post as a guest

Related