How to concatenate arrays

Join two vectors

      1 2 3,4 5 6
1 2 3 4 5 6

Append a scalar to a vector

      1 2 3,4
1 2 3 4

      0,1 2 3
0 1 2 3

Ravel a matrix into a vector

Monadic , (ravel) flattens any array into a vector:

      ,2 3⍴⍳6
1 2 3 4 5 6

See also: Reshape and ravel