Painfully simple org spreadsheet question

Question

I am an English teacher who is profoundly not good at math, but I want to make some simple calculations with an org-mode table. I've tried reading online, but am afraid the explanations are just not simple enough.

With the following table, what formula would I put in the final boxes to calculate the average grade for "draft" and the average grade for "final"? (That is, to calculate the mean of column 2 and the mean of column 3.)

| item    | draft | final|
|---------+-------+------|
| plot    |   2   |   3  |
| grammar |   3   |   4  |
|---------+-------+------|
| grade   |   ?   |   ?  |

Will the table recalculate with C-c * if I change one of the grades?

Thank you, steven arntson

Answer 1

You need 2 things here:

• The vmean function (stands for vector mean)
• The references @I and @II which stand for the first and second horizontal lines in the table.

So, with the cursor on the draft average cell, type :=vmean(@I..@II) and then RET. This will add the formula tag at the bottom of the table and the result in the table. Repeat for the other column.

| item    | draft | final |
|---------+-------+-------|
| plot    | 2     | 3     |
| grammar | 3     | 4     |
|---------+-------+-------|
| grade   | 2.5   | 3.5   |
#+TBLFM: @4$2=vmean(@I..@II)::@4$3=vmean(@I..@II)

If you are going to have many columns, you can also have only 1 formula for all columns thus:

#+TBLFM: @4$2..@4$>=vmean(@I..@II)

This means that all cells in row 4, from column 2 to the last column (denoted by $>) will have the same formula. By not including column references in the vmean() expressions, it automatically refers to the same column.

If you want to round your averages to, say, 2 decimal digits, you may add a format modifier:

#+TBLFM: @4$2..@4$>=vmean(@I..@II);%.2f

In this case, the modifier says to display floating point (fractional) numbers, with 2 digits after the decimal point.

Documentation for references.