Concatenate ascii/org tables with some different headings

Question

I want to concatenate two ascii tables (one below the other) that share some but not all column headings.

e.g.

Table 1

Head1 HeadA
1     a
2     b

Table 2

HeadA HeadFoo
c     bar

And the result would be

Head1 HeadA HeadFoo
1     a
2     b
c           bar

There is a babel library which does not quite do this, but it may have some helper functions (which I can't locate in emacs 24.5, but I guess I could copy paste the lisp into a file and read it).

Regarding the answers: Both Gastove and Tobias' answers work correctly. I chose Tobias only because it is more "pure".

Answer 1

I just add an emacs-lisp version to Gastove's answer. The code block is executed when you put point on the #+BEGIN_SRC line and input C-c C-c.

  Table 1
  #+name: first_tab
  | Head1 | HeadA |
  |     1 | a     |
  |     2 | b     |

  Table 2
  #+name: second_tab
  | HeadA | HeadFoo |
  | c     | bar     |

  #+BEGIN_SRC emacs-lisp :var first_tab=first_tab second_tab=second_tab
(require 'cl-lib)
(let ((combined-header (cl-union (car second_tab) (car first_tab) :test 'string-equal))
      (tbl-rearrange (lambda (new-header tab)
               (let ((old-header (car tab)))
             ;; TODO: Consider 'hline.
             (cl-loop
              for row in (cdr tab)
              collect (let ((alist (cl-mapcar 'cons old-header row)))
                    (mapcar
                     (lambda (col) (or (cdr (assoc col alist)) ""))
                     new-header)))))))
  (append
   (list combined-header)
   (funcall tbl-rearrange combined-header first_tab)
   (funcall tbl-rearrange combined-header second_tab)))
  #+END_SRC

  #+RESULTS:
  | Head1 | HeadA | HeadFoo |
  |     1 | a     |         |
  |     2 | b     |         |
  |       | c     | bar     |

Answer 2

My answer is an R-in-org-babel approach:

#+name: first_tab
| Head1 | HeadA |
|     1 | a     |
|     2 | b     |

#+name: second_tab
| HeadA | HeadFoo |
| c     | bar     |

#+BEGIN_SRC R :var a=first_tab b=second_tab :colnames t
  dfa <- data.frame(a)
  dfb <- data.frame(b)

  ## Get all names
  allnames <- union(names(dfa), names(dfb))

  addmissing <- function(df, namevec) {
    missing <- setdiff(namevec, names(df))
    for (n in missing) {
      df[, n] <- NA
    }
    return(df)
  }

  newdfa <- addmissing(dfa, allnames)
  newdfb <- addmissing(dfb, allnames)

  res <- rbind(newdfa, newdfb)

  return(res)
#+END_SRC

#+RESULTS:
| Head1 | HeadA | HeadFoo |
|-------+-------+---------|
|     1 | a     | nil     |
|     2 | b     | nil     |
|   nil | c     | bar     |