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Table of Contents

Table operations — filter or combine tables

This section within the library of babel provides table operations. See the documentation just below for details and working examples.

Author : Marc-Oliver Ihm <> Version : 1.0



The table operations (currently four) are grouped in two categories:

  • Filtering the rows of a single table: keeping or removing
  • Combining two tables into one: merging or intersecting

All four operations are demonstrated below.

Example tables

To demonstrate we need three tables: upper, lower and keys:

1 A
3 C
4 D
10 J
2 B
Position Letter
2 b
4 d
5 e
6 h

The tables upper and lower both have two columns and associate a position in the alphabet with the matching letter. E.g. the row "| 1 | A |" from table upper, just states that the letter "A" comes at position 1 in the alphabet.

Nearly the same is true for table lower, only that it contains lower case letters. Some of its letters (e.g. "b") have counterparts in table upper ("B"), some (e.g. "e") dont.

The table keys finally, contains keys (i.e. positions within the alphabet), that can be used to select rows from either table upper or lower.

Note, that tables may have column headings or not.

Filtering a table

  • Keeping rows

    Let's say, we want to select the upper-case letters (i.e. rows from the table upper), that are given in table keys (i.e. the first, second and fourth letter).

    This can be described as filtering table upper and keeping only those rows, that appear in table keys.

    As a babel-call, this reads:

    1 A
    4 D
    2 B

    ,which gives exactly those rows from table upper, that are specified in keys.

  • Removing rows

    Now, if on the contrary you want to filter table upper to remove any rows, which are given in table keys:

    Position t2c2
    3 C
    10 J

    ,which is the expected result.

    Please note, that the call contains the header argument ":colnames yes", which causes the result table to contain the headings "Position" and "t2c2". These headings are taken from the input-tables upper and keys. However, as upper does not contain any headings, the heading "t2c2" is generated artificially; it stands for "table 2 column 2".

    If you do not want to have column names in the result table, just leave out the header argument ":colnames yes" like in the first example. Note however, that ":colnames no" does not give the expected effect.

Combining tables

Now, lets have a look at the tables upper and lower alone and see how to combine them.

Note, that we only look at combining two tables for simplicity, however, all operations can be easily scaled up to seven tables.

  • Merging rows

    We have two tables, one with upper case letters and one with lower case. What now, if you want to have only one table, which contains both, upper and lower case letters ?

    You may want to merge them:

    Position t1c2 Letter
    1 A  
    2 B b
    3 C  
    4 D d
    5   e
    6   h
    10 J  

    This result combines both upper and lower case letters and lists them by their position within the alphabet.

  • Intersecting rows

    If you only want the rows, that are complete (i.e. have both upper and lower case letters) you may compute the intersection:

    2 B b
    4 D d

    ,which has only those keys and letters, that appear in both tables.

    Note, that we have ommitted the headeragument ":colnames yes" so that the result table has no headings.


This section is not required if you just want to use table operations as described above. Only if you are curious about its implementation or development, you might want to have a look.


Here is the actual lisp code, that implements the functionality of table operations.

  • table-operations-filter
    • Directly callable blocks
      (let ((filter-and-table (list filter table)))
        (lob-table-operations-filter 'keep filter-and-table))
      (let ((filter-and-table (list filter table)))
        (lob-table-operations-filter 'remove filter-and-table))
    • Included defuns
      (defun lob-table-operations-filter (what filter-and-table)
        "Internal function for table operations in orgmode library of babel"
        (let (keys
          ;; seperate headings from rest of tables
          (setq headings-all-tables 
                (lob-table-operations-helper-get-headings filter-and-table))
          ;; extract arguments
          (setq filter (car filter-and-table))
          (setq table (cadr filter-and-table))
          ;; remove hlines
          (setq table (org-babel-del-hlines table))
          (setq filter (org-babel-del-hlines filter))
          (setq keys (mapcar 'car filter))
          ;; start result with headings (reversed)
          (setq result-table (cons 'hline (cons headings-all-tables nil)))
          (dolist (line table) ; loop over table lines 
            (if (equal (not (not (member (car line) keys))) 
                       (equal what 'keep)) ; 'keep or 'remove ?
                (setq result-table (cons line result-table))))
          (nreverse result-table)))
  • table-operations-combine
    • Directly callable blocks
      (let ((tables (list t1 t2 t3 t4 t5 t6 t7)))
        (lob-table-operations-combine 'merge tables))
      (let ((tables (list t1 t2 t3 t4 t5 t6 t7)))
        (lob-table-operations-combine 'intersect tables))
    • Included defuns
      (defun lob-table-operations-combine (what tables)
        "Internal function for table-operations in orgmode library of babel"
        (let (is-all-numbers                 
          ;; remove possible empty trailing tables
          (setq rest-of-tables tables)
          (while (cadr rest-of-tables) (setq rest-of-tables (cdr rest-of-tables)))
          (setcdr rest-of-tables nil)
          ;; seperate headings from rest of tables
          (setq headings-all-tables (lob-table-operations-helper-get-headings 
          (setq result-table (cons 'hline (cons headings-all-tables nil)))
          ;; remove all remaining hlines
          (setq tables (mapcar 'org-babel-del-hlines tables))
          ;; Find out, if all keys in all tables are numbers or if 
          ;; there are strings among them
          (setq is-all-numbers
                (catch 'not-a-number
                  (dolist (table tables) 
                    (dolist (line table) 
                      (unless (numberp (car line)) 
                        (throw 'not-a-number 'nil))))
          (setq format-specifier (if is-all-numbers "%g" "%s"))
          ;; Prepare functions to treat table contents in a unified way
          (flet ((convert (x) 
                          (if is-all-numbers
                            (if (numberp x) 
                                (number-to-string x) 
                 (less-than (x y) 
                            (if is-all-numbers (< x y) 
                              (string< (convert x) 
                                       (convert y))))
                 (compare (x y) 
                          (if is-all-numbers (= x y) 
                            (string= (convert x) 
                                     (convert y)))))
            ;; sort tables
            (setq tables (mapcar (lambda (table) 
                                   (sort table (lambda (x y) 
                                                 (less-than (car x) 
                                                            (car y))))) 
            ;; compute and remember table widths
            (setq widths-of-tables (mapcar (lambda (x) (length (car x))) tables))
            ;; copy initially and shorten below
            (setq rests-of-tables (copy-list tables))
            ;; loop as long as the rest of table still contains lines
            (while (progn 
                     ;; find lowest key among all tables, which is the key for the
                     ;; next line of the result
                     (setq current-key nil)
                     (setq current-key-in-intersection 't) ; remember for later
                     (dolist (rest-of-table rests-of-tables) ; loop over all tables
                       (when (and rest-of-table ; and compare against all keys
                                  (or (null current-key) 
                                      (less-than (caar rest-of-table) 
                         (setq current-key (caar rest-of-table))))
                (setq result-line (list current-key))
                ;; go through all tables and collect one line for the result table
                (setq i 0)                      ; table-count
                ;; cannot use dolist like above, because we need to modify the
                ;; cons-cells
                (setq rest-of-rests-of-tables rests-of-tables)
                (while (progn
                         (setq rest-of-table (car rest-of-rests-of-tables))
                         (incf i)
                         ;; if table contains current key 
                         (if (and rest-of-table
                                  (compare current-key (caar rest-of-table)))
                             ;; then copy rest of line
                             (progn (nconc result-line (cdar rest-of-table))
                                    ;; and shorten rest
                                    (setcar rest-of-rests-of-tables 
                                            (cdar rest-of-rests-of-tables))
                                    ;; and check, if current-key appears again
                                    (when (and (caadr rest-of-table)
                                               (compare current-key 
                                                        (caadr rest-of-table)))
                                      (error (concat "Key '" 
                                                     "' appears twice within "
                                                     "input table %i") 
                                             (convert current-key) i)
                           ;; otherwise fill with nil and do not shorte
                           ;; rest of table
                             (setq current-key-in-intersection nil)
                             (nconc result-line (make-list (1- 
                                                            (elt widths-of-tables 
                                                                 (1- i))) 
                         (setq rest-of-rests-of-tables 
                               (cdr rest-of-rests-of-tables))
                         rest-of-rests-of-tables)) ; condition for loop
                (if (or (eq what 'merge) current-key-in-intersection)
                    ;; store away line
                    (setq result-table (cons  
            (nreverse result-table))))
  • Common helper functions
    (defun lob-table-operations-helper-get-headings (tables)
      "Internal function for table-operations in orgmode library of babel"
      (let ((rest-of-tables tables)
            (i 1)
        (while rest-of-tables 
            (setq table (car rest-of-tables))
            (if (eq (cadr table) 'hline)
                ;; second line is a hline, so first is a heading
                  ; take headings from first table row
                  (setq headings-one-table (cdar table)) 
                  (unless heading-of-key (setq heading-of-key (caar table)))
                  (unless (string= heading-of-key (caar table))
                    (error "Name of first column is not the same in all tables"))
                  (setcar rest-of-tables 
                          (cdar rest-of-tables))) ; and shorten rest
              ;; table does not contain headings, so make them up
              (setq headings-one-table 
                     (lambda (x) (format "t%dc%d" i x))
                     (number-sequence 2 (length (car table))))))
            (setq headings-all-tables (append headings-all-tables 
            (setq rest-of-tables (cdr rest-of-tables))
            (incf i)
            rest-of-tables)) ; condition for while loop
        (unless heading-of-key (setq heading-of-key "key"))
        (setq headings-all-tables (cons heading-of-key headings-all-tables))
  • Debugging and testing
    • Clean up
        (while (re-search-forward "^#\\+results:.*\n\\(^\|.+\n\\)*\n" nil t)
          (replace-match ""))
    • Byte Compilation

      (byte-compile 'lob-table-operations-combine) (byte-compile 'lob-table-operations-filter)


  • Versions and history

    [2012-03-18 Sun] Version 1.0:

    • Added handling of hlines and table headings

    [2012-01-07 Sat] Version 0.01:

    • Restructured as a single org-file; no special .el-file needed any more
    • Combined and restructured documentation and implementation
  • Bugs and Todos
    • [X] Brush up documentation
    • [X] Stay below 80 columns
    • [X] Tests with more than two columns per table
    • [X] Tests with more than two tables for merging
    • [X] Handle optional table captions
    • [X] Handle hlines
    • [X] flet within lob-table-operations-combine
    • [-] flet within directly callable blocks; try to avoid global functions Not feasible, because that hinders debugging to much
    • [X] Use :results silent
  • Testcases
    Position c1 c2 c3 c4
    1 A1 A2 A3 A4
    3 C1 C2 C3 C4
    4 D1 D2 D3 D4
    10 J1 J2 J3 J4
    2 B1 B2 B3 B4
    2 b1 b2 b3 b4
    4 d1 d2 d3 d4
    5 e1 e2 e3 e4
    6 h1 h2 h3 h4
    2 Bb1 Bb2 Bb3 Bb4
    6 Hh1 Hh2 Hh3 Hh4
    4 Dd1 Dd2 Dd3 Dd4
    10 Jj1 Jj2 Jj3 Jj4
    1 A1 A2 A3 A4
    4 D1 D2 D3 D4
    2 B1 B2 B3 B4
    Position t2c2 t2c3 t2c4 t2c5
    5 e1 e2 e3 e4
    6 h1 h2 h3 h4
    Position c1 c2 c3 c4 t2c2 t2c3 t2c4 t2c5
    1 A1 A2 A3 A4        
    2 B1 B2 B3 B4 b1 b2 b3 b4
    3 C1 C2 C3 C4        
    4 D1 D2 D3 D4 d1 d2 d3 d4
    5         e1 e2 e3 e4
    6         h1 h2 h3 h4
    10 J1 J2 J3 J4        
    2 B1 B2 B3 B4 b1 b2 b3 b4
    4 D1 D2 D3 D4 d1 d2 d3 d4
    Position c1 c2 c3 c4 t2c2 t2c3 t2c4 t2c5 t3c2 t3c3 t3c4 t3c5
    1 A1 A2 A3 A4                
    2 B1 B2 B3 B4 b1 b2 b3 b4 Bb1 Bb2 Bb3 Bb4
    3 C1 C2 C3 C4                
    4 D1 D2 D3 D4 d1 d2 d3 d4 Dd1 Dd2 Dd3 Dd4
    5         e1 e2 e3 e4        
    6         h1 h2 h3 h4 Hh1 Hh2 Hh3 Hh4
    10 J1 J2 J3 J4         Jj1 Jj2 Jj3 Jj4
    2 B1 B2 B3 B4 b1 b2 b3 b4 Bb1 Bb2 Bb3 Bb4
    4 D1 D2 D3 D4 d1 d2 d3 d4 Dd1 Dd2 Dd3 Dd4
  • Keeping the margins

    (setq-default fill-column 80) (column-marker-3 80)

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