[O] Filterring a table for values in a list

[sven.garbade]

Hi,

based on a post on
http://emacs.stackexchange.com/questions/20129/how-can-i-filter-table-in-org-mode
about filtering a table row-wise, I want to write a filter to select rows
which matches some values in a list:

#+NAME: table1
| col1  | col2 | col3 | col4 | col5 |
|-------+------+------+------+------|
| row0  |    0 | CH   | CH   |    0 |
| row1  |    2 | D    | CN   |    5 |
| row2  |    4 | USA  | PL   |   10 |
| row3  |    6 | CN   | D    |   15 |
| row4  |    8 | JP   | USA  |   20 |
| row5  |   10 | PL   | PL   |   25 |
| row6  |   12 | USA  | JP   |   30 |
| row7  |   14 | D    | CN   |   35 |
| row8  |   16 | PL   | USA  |   40 |
| row9  |   18 | CN   | D    |   45 |
| row10 |   20 | CH   | CH   |   50 |

I like to filter col4 for "USA" and "CN" 

#+NAME: my-filter
#+BEGIN_SRC elisp :var tbl=table1 val='("" "USA" "CN")  :colnames y
  (cl-loop for row in tbl
           if (member (nth 3 row) val)
           collect row into newtbl
           finally return newtbl)
#+END_SRC

with result

#+RESULTS: my-filter
| row1 |  2 | D  | CN  |  5 |
| row4 |  8 | JP | USA | 20 |
| row7 | 14 | D  | CN  | 35 |
| row8 | 16 | PL | USA | 40 |

My questions:

1) How can I preserve the column names in the result? The code on
http://emacs.stackexchange.com/questions/20129/how-can-i-filter-table-in-org-mode
preserves the table header.
2) Without the "" in the list, only rows matching the last element "CN"
are selected. So I think the code is wrong.

Are there any ideas to improve the code?

Thanks, Sven