List manipulation: subsets from a ragged array

Questions
1

Suppose I have the following list:

originalList = {{a},{b,c},{d,e,f}}

Now, I want to create a new list such that each element of this new list is also list containing 3 elements. Each of this 3 elements comes from different subsets of the originalList. In other words, how do I create the following list:

{{a,b,d},{a,b,e},{a,b,f},{a,c,d},{a,c,e},{a,c,f}}

Thanks in advance.

2

Sounds like Outer:

originalList = {{a}, {b, c}, {d, e, f}};
Flatten[Outer[List, Sequence @@ originalList], 2]
Out[]= {{a, b, d}, {a, b, e}, {a, b, f}, {a, c, d}, {a, c, e}, {a, c, f}}
3

Though Outer is definitely possible, I would definitely used Tuples in this case!

originalList = {{a}, {b, c}, {d, e, f}}
Tuples[originalList]

much much easier!

4

Yes, this is neat!

5

Also note that Tuples will generally be faster than Outer for this operation. Generally Outer is kinda slow because it generally(always?) does not vectorizes calculations… which is sometimes possible…