Answered
If l1={0,1,2,3,5}
and l2=Sequence(Sequence(If(Element(l1, j) > 0, "A", ""), k, 1, Element(l1, j)), j, 1, Length(l1))={{},{A},{A,A},{A,A,A},{A,A,A,A,A}}
but why is l3=Sequence(Sum(Element(l2, i)), i, 1, Length(l2))={0,?,?,?,?}
i am looking for {"","A","AA","AAA","AAAAA"}
I believe if sum(sequence("A",i,1,5)) works then the command for l3 should also work.
The same question 
Oh, same question again. I explained it in the other thread.
In Sequence() and Zip() all elements must be of the same type.
The above rule does not apply in l3. Sum(Element(l2,1)) has the value 0 and therefore the type "numeric" but the remaining elements have the type "text".
l2 must therefore be adjusted so that element(l2,1) gets the value {""} instead of {}. Then all elements have the same type "text".
In the attachment, three alternatives l2A, l2B, l2C are listed, all of which lead to the desired result in l3.
Note: My post and artydent's post overlapped in time (for me).
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