How to combine 2 lists using LINQ?

Question

Env.: .NET4 C#

Hi All,

I want to combine these 2 lists : { \"A\", \"B\", \"C\", \"D\" } and { \"1\", \"2\", \"3\" }

into this o

Answer 1

Use SelectMany when you want to form the Cartesian product of two lists:

aList.SelectMany(a => bList.Select(b => a + b))

Answer 2

Essentially, you want to generate a cartesian product and then concatenate the elements of each 2-tuple. This is easiest to do in query-syntax:

var cartesianConcat = from a in seq1
                      from b in seq2
                      select a + b;

Answer 3

SelectMany is definitely the right approach, whether using multiple "from" clauses or with a direct call, but here's an alternative to Hightechrider's use of it:

var result = aList.SelectMany(a => bList, (a, b) => a + b);

I personally find this easier to understand as it's closer to the "multiple from" version: for each "a" in "aList", we produce a new sequence - in this case it's always "bList". For each (a, b) pair produced by the Cartesian join, we project to a result which is just the concatenation of the two.

Just to be clear: both approaches will work. I just prefer this one :)

As to whether this is clearer than the query expression syntax... I'm not sure. I usually use method calls when it's just a case of using a single operator, but for Join, GroupJoin, SelectMany and GroupBy, query expressions do simplify things. Try both and see which you find more readable :)