Question

I need to use If inside of a Table loop, e.g. Table[If[i< 3, i], {i, 5}] will give {1, 2, Null, Null, Null}

But I want the result to be {1,2}.

Any fix for this?

EDIT:
What if we consider Table[If[i< 3, f[i]], {i, 5}] which gives {f[1], f[2], Null, Null, Null}

Answer 1

Concisely:

Table[If[i < 3, i, ## &[]], {i, 5}]

This works because the function ## & does not immediately evaluate.

## & is a “vanishing” function.

{1, 2, ## &[], 3, 4}

----> {1, 2, 3, 4}

See SlotSequence for more information.