Deleting duplicates in an org-table column

Question

I wanted to preserve the first row value while deleting all subsequent repeated values in the sequence column ($5) as in the MWE below:

| ID | M | D | P | sequence     | item        |
|----+---+---+---+--------------+-------------|
|  1 | 1 | 1 | 1 | CGGCCTT      | 38/96       |
|  2 | 1 | 1 | 1 | CGGCCTT      | ger24       |
|  3 | 1 | 1 | 1 | CGGCCTT      | 31/54       |
|  4 | 1 | 1 | 1 | CGGCCTT      | 34/34       |
|  5 | 1 | 1 | 1 | CGGCCTT      | 43/20       |
|  6 | 1 | 1 | 1 | CGGCCTT      | 45/134      |
| 23 | 1 | 1 | 2 | TTAAACCGG    | 53/36       |
| 23 | 1 | 1 | 2 | TTAAACCGG    | 53/47       |
| 24 | 1 | 1 | 2 | TTAAACCGG    | 13/31       |
| 25 | 1 | 1 | 2 | TTAAACCGG    | 33/72       |
| 26 | 1 | 1 | 2 | TTAAACCGG    | 49/31       |
| 27 | 1 | 1 | 2 | TTAAACCGG    | 47/62       |
| 28 | 1 | 1 | 2 | TTAAACCGG    | 53/3        |
| 29 | 1 | 1 | 2 | TTAAACCGG    | 59/29       |
| 30 | 1 | 1 | 2 | TTAAACCGG    | 47/24       |
| 31 | 1 | 1 | 3 | CCGGTTAAA    | 52/63       |
| 32 | 1 | 1 | 3 | CCGGTTAAA    | 35/90       |
| 33 | 1 | 1 | 3 | CCGGTTAAA    | 67/3        |
| 34 | 1 | 1 | 3 | CCGGTTAAA    | 38/76       |
| 35 | 1 | 2 | 1 | TTCCGGAATTTT | 41/30       |
| 36 | 1 | 2 | 1 | TTCCGGAATTTT | 18/10       |
| 37 | 1 | 2 | 1 | TTCCGGAATTTT | 42/35       |
| 38 | 1 | 2 | 1 | TTCCGGAATTTT | 43/33       |
| 39 | 1 | 2 | 1 | TTCCGGAATTTT | ger30       |
| 40 | 1 | 2 | 2 | TTCCGGAATTTT | 49/31       |

Desired Output

| ID | M | D | P | sequence     | item     |
|----+---+---+---+--------------+----------|
|  1 | 1 | 1 | 1 | CGGCCTT      | 38/96    |
|  2 | 1 | 1 | 1 |              | ger24    |
|  3 | 1 | 1 | 1 |              | 31/54    |
|  4 | 1 | 1 | 1 |              | 34/34    |
|  5 | 1 | 1 | 1 |              | 43/20    |
|  6 | 1 | 1 | 1 |              | 45/134   |
| 23 | 1 | 1 | 2 | TTAAACCGG    | 53/36    |
| 23 | 1 | 1 | 2 |              | 53/47    |
| 24 | 1 | 1 | 2 |              | 13/31    |
| 25 | 1 | 1 | 2 |              | 33/72    |
| 26 | 1 | 1 | 2 |              | 49/31    |
| 27 | 1 | 1 | 2 |              | 47/62    |
| 28 | 1 | 1 | 2 |              | 53/3     |
| 29 | 1 | 1 | 2 |              | 59/29    |
| 30 | 1 | 1 | 2 |              | 47/24    |
| 31 | 1 | 1 | 3 | CCGGTTAAA    | 52/63    |
| 32 | 1 | 1 | 3 |              | 35/90    |
| 33 | 1 | 1 | 3 |              | 67/3     |
| 34 | 1 | 1 | 3 |              | 38/76    |
| 35 | 1 | 2 | 1 | TTCCGGAATTTT | 41/30    |
| 36 | 1 | 2 | 1 |              | 18/10    |
| 37 | 1 | 2 | 1 |              | 42/35    |
| 38 | 1 | 2 | 1 |              | 43/33    |
| 39 | 1 | 2 | 1 |              | ger30    |
| 40 | 1 | 2 | 2 |              | 49/31    |

My unsuccessful trial was by trying:

#+TBLFM: $5='(delete-dups (list @2..@26));L

Side note: I noticed one can hit C-c ^ while the pointer is on the desired column header to invoke sorting options, according to date, alphabet, but I noticed also there is the [f]unction among them , I wonder how can one apply this function to eliminate duplicates in any column of the org-table. Your help is much appreciated.

More Experiments

When I try this in block code after adding quotations to the elements:

#+BEGIN_SRC emacs-lisp
(delete-dups (list "CGGCCTT"  "CGGCCTT"  "CGGCCTT"  "CGGCCTT"  "CGGCCTT"  "CGGCCTT" "TTAAACCGG" "TTAAACCGG" "TTAAACCGG" "TTAAACCGG" "TTAAACCGG" "TTAAACCGG" "TTAAACCGG" "TTAAACCGG" "TTAAACCGG" "CCGGTTAAA" "CCGGTTAAA" "CCGGTTAAA" "CCGGTTAAA" "TTCCGGAATTTT" "TTCCGGAATTTT" "TTCCGGAATTTT" "TTCCGGAATTTT" "TTCCGGAATTTT" "TTCCGGAATTTT"))
#+END_SRC

This will give me this result after evaluation:

("CGGCCTT" "TTAAACCGG" "CCGGTTAAA" "TTCCGGAATTTT")

Which is sort of what I want, but wait this is not the desired effect unless somehow there will be also empty elements in the list to replace those duplicate removed elements, am I right? Besides quotation marks should be added somehow in the table formula. It seems applying all this in table formula is far more complicated than I thought.

Answer 1

This can easily be done with a memory that remembers the last used sequence. I use a global variable my-var for that purpose in the following.

#+TBLFM: $5='(if (and (/= @# 2) (string= @0 my-var)) "" (setq my-var @0))

The failing test for (/= @# 2) at the beginning serves for the initialization of my-var and subsequent successful tests for (string= @0 my-var) replace duplicates by the empty string.