Question

I have some LINQ code that extracts bookmarks from PDFs that match a certain naming convention (using Aspose.Pdf):

IOrderedEnumerable<Bookmark> magicBookmarks = (
    from    bookmark in allBookmarks.AsEnumerable()
    where   bookmark.Title.StartsWith(MAGIC_PHRASE) 
    // ...  other criteria
    orderby bookmark.PageNumber ascending
    select  bookmark
);

The Bookmark class has a property called PageNumber that gets the page number where a bookmark starts. In my situation, a bookmark can represent a section of 1…n pages.

What I’d like to do is transform this sequence into another sequence of Tuple<int, int> (or some comparable “pair” structure) where Item1 of each pair equals the PageNumber value of the corresponding element in the source sequence and Item2 equals the `PageNumber’ value of the next element in the source sequence minus 1 (for the sake of this exercise, assume that all Bookmarks in the source sequence occur in succession in the document from which they were extracted).

In short, I want the end result to be a sequence of pairs that represent the start and end pages of each bookmarked PDF section.

Answer 1

You could use Enumerable.Zip for this by zipping the enumeration with itself just skipping the first element:

var results = magicBookmarks.Zip(magicBookmarks.Skip(1), 
                                 (a, b) => new 
                                           { 
                                             PageNumber = a.PageNumber, 
                                             PageNumberNext = b.PageNumber - 1 
                                           });

foreach (var item in results)
{
    Console.WriteLine("Page: {0}, Next: {1}", item.PageNumber, item.PageNumberNext);
}