Question: In Excel it is possible to write a function looking like that:

```
=SUM(A1:INDEX(...))

```

Where the end of the range of the data to sum is dynamically defined by the result of the `INDEX` function.

The same function in Numbers gives an invalid reference error (the `INDEX` function is working well by itself).

Is there another way in Numbers to define a range as a result of a function?

Answer: 
No, because `index` doesn't return a **cell address**. You'll need to use a modifier to return the address of your selection. 

Try using a `match` nested in an `=address` rather than an index. I can't provide an answer with an example because you haven't described your data set.
You could also use something like 

```
=SUM(OFFSET(A1,0,0,n))

```

Where *n* is the height of the columnar range to sum starting at `A1`. `OFFSET` is a volatile function, so avoid if that bothers you.