LINQ query Concat values to list of type string

Question

Is there a more efficient way to handle this?

List<String> lstReferences = (from f in 
                            (from section in courseSectionToCreate.SectionsToAdd
                                select new {
                                            ReferenceNumber = section.Course.CourseNumber.Substring(0, 5) + "." +
                                                section.Course.CourseNumber.Substring(5) + "." +
                                                section.Session + "." +
                                                section.Year + "." +
                                                section.SectionNumber + ";"
                                            })
                            select f.ReferenceNumber).ToList();

strReferenceNumber = lstReferences.Aggregate((a, b) => a + ", " + b);

jason · Accepted Answer · 2011-02-14 19:21:24Z

2

Yes, you definitely don't want to be using Aggregate here. That is O(n^2) (it's Schlemiel the Painter's algorithm). Instead:

string referenceNumber = String.Join(", ", lstReferences);

This is better because String.Join will use a StringBuilder internally.

answered Feb 14, 2011 at 19:21

jason

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Jeff Mercado · Accepted Answer · 2011-02-14 19:45:27Z

0

You can replace all that with this:

var strReferenceNumber =
    String.Join(", ",
        courseSectionToCreate.SectionsToAdd.Select(s =>
            String.Join(".", 
                s.Course.CourseNumber.Substring(0, 5),
                s.Course.CourseNumber.Substring(5),
                s.Session,
                s.Year,
                s.SectionNumber) + ";"
        )
    );

edited Feb 14, 2011 at 19:45

answered Feb 14, 2011 at 19:34

Jeff Mercado

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1 Comment

Yellowstone Secrets Over a year ago

Thanks for this answer, it appears to be processing the fastest on my machine.

Ani · Accepted Answer · 2011-02-14 19:27:23Z

0

How about:

var lstReferences = from section in courseSectionToCreate.SectionsToAdd     
                    let courseNumber = section.Course.CourseNumber                           
                    let toJoin = new object[] 
                    { 
                       courseNumber.Substring(0, 5),
                       courseNumber.Substring(5),
                       section.Session,
                       section.Year,
                       section.SectionNumber
                    }
                    select string.Join(".", toJoin) + ";" 

var strReferenceNumber = string.Join(", ", lstReferences);

answered Feb 14, 2011 at 19:27

Ani

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10 Comments

jason Over a year ago

I doubt (but don't know) that that will cooperate with LINQ to SQL (or other queryable providers like that). That is an important consideration.

Ani Over a year ago

@Jason: Is this LINQ to SQL? Doesn't look like it, though I could be wrong.

Ani Over a year ago

@Jason: It could be. Was an impression; there doesn't appear to be a data-context.

Jeff Mercado Over a year ago

@Jason: LINQ to SQL can definitely handle the string methods used here (String.Join(), String.Concat() and String.Substring()) so it's not a problem.

jason Over a year ago

@Jeff M: Are you sure about String.Join, especially the way that it is being invoked?

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