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Tracking rental-income via org-mode

7 February 2020 21:20

I've been enjoying the process of exploring org-mode recently as I keep running into references to it. Often these references are people questioning me: why don't you just use 'org-mode' instead of this crazy-thing you're managing yourself?

As one concrete example, no pun intended, I look after some flats, and every month I update my records to keep track of things. Until now I've used a set of markdown files, one for each property, and each has details of tenants, income, repairs, & etc. I've now ported these to org-mode-files. The first thing I did was create a table for each year so this year's might look like this:

#+NAME: 2020
| Month     | Tenant |    Rent | Mortgage | Housing Company |
|-----------+--------+---------+----------+-----------------|
| January   | Bob    |     250 |   150.00 |           75.00 |
| February  | Bob    |     250 |   150.00 |           75.00 |
| March     |        |         |          |                 |
| April     |        |         |          |                 |
| May       |        |         |          |                 |
| ..        |    ... |     ... |    ....  |           ...   |
|-----------+--------+---------+----------+-----------------|
| Totals    |        |  500.00 |   300.00 |          150.00 |
#+TBLFM: @>$3=vsum(@I..@II);%0.2f::@>$4=vsum(@I..@II);%0.2f::@>$5=vsum(@I..@II);%0.2f

Here you see the obvious:

  • I've declared a table with a name 2020.
  • I've got totals of the various columns at the bottom of the table.
  • I only populate each row on the day when I check to see whether rent has been paid by the lovely tenant.
    • So all the rows past the current-month are empty.

This is probably all very familiar to org-mode users, let us go a little further, we have a table named 2020, let us create a new table called 2020-totals to show more useful figures:

#+NAME: 2020-totals
| Year |  Income | Expenses | Profit |
|------+---------+----------+--------|
| 2020 |  500.00 |   450.00 |  50.00 |
#+TBLFM: @2$2=remote(2020,@>$3);%.2f::@2$3=remote(2020,@>$4)+remote(2020,@>$5);%.2f::@>$4=@>$2-@$3;%.2f

Again nothing amazing here:

  • We reference "remote"-values (i.e values from a different table).
  • We look for things like "row:@>", "column:$3" which means "row:last column:3rd".
    • The bottom line should be split by :: to make sense, like so:
      • @2$2=remote(2020,@>$3);%.2f
      • %.2f is a format-string, to control how many decimal places to show.
      • @2$3=remote(2020,@>$4) + remote(2020,@>$5);%.2f
      • Expenses are "Mortgage" + "Housing Company"
      • i.e. The contents of the fourth and fifth column.
      • @>$4=@>$2-@$3;%.2f
  • The end result is that we have sum of income, sum of expenses, and the difference between them is the profit (or loss).

Of course I've got records going back a while, so what we really want is to have a complete/global table of income/expenses and profit (or loss if that's a negative figure). We'll assume there are multiple tables in our document, a pair for each year "2019", "2019-totals", etc. To generate our global income/expenses/property we just have to sum the columns for each of the tables which have names matching the pattern "*-totals". Here we go:

#+NAME: income-expenses-profit
|----------+-----------|
| Income   | €10000.00 |
| Expenses | € 8000.00 |
| Profit   | € 2000.00 |
|----------+-----------|
#+TBLFM: @1$2='(car (sum-field-in-tables "-totals$" 1));€%.2f::@2$2='(car (sum-field-in-tables "-totals$" 2));€%.2f::@3$2='(car (sum-field-in-tables "-totals$" 3));€%.2f

Once again there are three values here, and splitting by :: makes them more readable:

  • @1$2='(car (sum-field-in-tables "-totals$" 1));€%.2f
  • @2$2='(car (sum-field-in-tables "-totals$" 2));€%.2f
  • @3$2='(car (sum-field-in-tables "-totals$" 3));€%.2f

In short we set the value row:X, column:2 to be the value of evaluating the Emacs lisp expression (car (sum-field-in-tables .., rather than using the built-in table support from org-mode. I did have to write that function myself to do the necessary table-iteration and field summing, but with the addition of naive filtering-support that turned out to be pretty useful as we'll see later:

(defun sum-field-in-tables (pattern field &optional filter)
  "For every table in the current document which has a name matching the
supplied pattern perform a sum of the specified column.

If the optional filter is present then the summing will ignore any rows
which do not match the given filter-pattern.

The return value is a list containing the sum, and a count of those
rows which were summed."

Using this function I managed to achieve what I wanted, and also as a bonus I could do clever things like show the total income/payments from a given tenant. If you refer back to the 2020-table you'll see there is a column for the tenant's name. So I can calculate the total income from that tenant, and the number of payments by summing:

  • All tables with a name "^:digit:$"
    • column 3 (i.e. rent)
    • where rows match the filter "Bob"

The end result is another table like so:

#+NAME: tenants-paid
| Tenant    | Rent Paid | Rented Months |
|-----------+-----------+---------------|
| [[Alice]] | €1500.00  |             6 |
| [[Bob]]   | €1500.00  |             6 |
| [[Chris]] | €1500.00  |             6 |
#+TBLFM: $2='(car (sum-field-in-tables "^[0-9]*$" 2 $1));€%0.2f::$3='(cdr (sum-field-in-tables "^[0-9]*$" 2 $1))

This works because the table-sum function returns two things, the actual sum of the rows, and the number of rows that were summed:

  • So (car (sum-field-in-tables .. returns the actual sum. The rent the person has paid, total.
  • And (cdr (sum-field-in-tables .. returns the number of payments that have been made by the tenant with the given name.

The only thing I had to do explicitly was to add the rows for Alice, Bob, and Chris to this table.

Anyway this is all rather cool, and I'm pretty happy, though if I could have avoided writing lisp I'd have been a little happier. Now I guess I need to choose between one of two approaches:

  • Do I put the lisp function in the report-file itself?
    • Which then needs to be evaluated when the file is loaded - simple enough.
  • Or do I drop it inside ~/.emacs/init.md - which is good for me, but means the file isn't self-contained for others?

I'll probably continue to play with this a little more over the next few days/weeks. Exporting to HTML and PDF worked like a charm, once I configured some minor things and setup a couple of sections of my documents with a :noexport: tag.

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