it misses unit tests, I need to make the collapse optional, and I need 
to hear from users what they think of it.  this patch allows me to write 
a table like the following, having a three-lines header:

|  n | data | prove, |  casi, | ratio |   prove, |    casi, |
|    |      | valore | valore |       |    media | media |
|    |      | diario | diario |       | corrente | corrente |
|----+------+--------+--------+-------+----------+----------|

and this is seen as a single header line.

|  n | data | prove, valore diario | casi, valore diario | ratio | 
prove, media corrente | casi, media corrente |
|----+------+----------------------+---------------------+-------+-----------------------+----------------------|

I find it helpful, because this way my columns stay narrower.

as it is, ¡it fails on headerless tables!

I have not yet clear what's the best approach to handling headerless 
tables, was thinking of a org-table-max-collapse-header variable, which 
you would set to the number of lines which you are maximally expecting 
to collapse into the leading header line.  Or maybe an extra option to 
org-plot, where you would state if headers need be collapsed.

or we already had ways to achieve this same thing, and I missed them all?

best regards,

MF