Interpolate

Plugins for Beancount to interpolate one entry into many for smooth graphs. Includes:

• split - dublicates all entry postings over time with fraction of original value.
• spread - generates new entries to spread Income or Expense postings over time (difference is accumulated and cleared against Liabilities:Current or Assets:Current accounts).

For tax-compatible yearly depreciation take a look at this plugin by Alok Parlikar under MIT license.

Install

pip3 install beancount-interpolate --user

Or copy to path used for python. For example, $HOME/.local/lib/python3.4/site-packages/beancount-interpolate/* would do on Debian. If in doubt, look where beancount folder is and copy next to it.

Details

Spread

Problem

Let's say John has only two activities

1. 10 EUR daily food expenses
2. 300 EUR net monthly salary (day 15 in next month)

If we plot John's wealth, it would look like zig-zag and be negative between -150 EUR (right after salary) and -450 EUR (right before), that is big and unstable error for your current wealth. And there could be more incomes/expenses with various 'periods'. In most complicated case John would have multiple income/expense sources with various lenght periods that are unsynchronised, but John wants dashboard with graph of correct daily report on his wealth.

Possible solutions:

1. Do nothing and ackowledge the 0-300 EUR error. IMO Is ok only if error is relatively small.
2. Do nothing and restrict yourself to do analysis at regular intervals when error is smallest (for example right after salary) and apply known corrections (for example, +150 EUR because it's already middle of month). IMO it is ok only if all periods are synchronised.
3. Record 10 EUR income to cash daily. But that violates 'after fact' principle that IMO is more important and IMO that's too much effort and transaction spam.
4. Record 10 EUR income to 'work token' assets daily but IMO that's still too much effort and transaction spam.
5. Let plugin do No.4 for you. (This repository)

How to use

Copy/paste variables for plugin and edit for yourself.

; Set defaults.
plugin "beancount-interpolate.spread" "{
    'account_income': 'Liabilities:Current',
    'account_expenses': 'Assets:Current',
    'aliases_after': ['spreadAfter', 'spread'],
    'default_period': 'Month',
    'default_method': 'SL',  # Straight Line
    'min_value': 0.05,  # cannot be smaller than 0.01
    'max_new_tx': 9999,
    'suffix': ' (spread %d/%d)',
    'tag': 'spreaded'
}"

Add meta or tags to your transactions. All folllowing transactions does the same.

; Explicit.
2016-06-15 * "The Company" "Simplest salary entry"
    Income:TheCompany:NetSalary     -310.00 EUR
        spreadAfter: "Month @ 2016-05-01"
    Assets:MyBank:Checking           310.00 EUR

; Transaction meta applies to all Income/Expense postings if they don't have their own.
2016-06-15 * "The Company" "Simplest salary entry"
    spreadAfter: "Month @ 2016-05-01"
    Income:TheCompany:NetSalary     -310.00 EUR
    Assets:MyBank:Checking           310.00 EUR

; Use spreadBefore if that reads better in your case.
2016-06-15 * "The Company" "Simplest salary entry"
    spreadBefore: "Month @ 2016-05-31"
    Income:TheCompany:NetSalary     -310.00 EUR
    Assets:MyBank:Checking           310.00 EUR

; Use default period.
2016-06-15 * "The Company" "Simplest salary entry"
    spreadAfter: "2016-05-01"
    Income:TheCompany:NetSalary     -310.00 EUR
    Assets:MyBank:Checking           310.00 EUR

; Use date of transaction.
2016-06-15 * "The Company" "Simplest salary entry"
    spreadAfter: "Month"
    Income:TheCompany:NetSalary     -310.00 EUR
    Assets:MyBank:Checking           310.00 EUR

; Use date of transaction and default period. Beware the different transaction date.
2016-05-01 * "The Company" "Simplest salary entry" #spreadAfter
    Income:TheCompany:NetSalary     -310.00 EUR
    Assets:MyBank:Checking           310.00 EUR

What happens

First, plugin edits the original transaction like this:

2016-05-01 * "The Company" "Simplest salary entry (Generated by interpolate-spread)" #spread
    Liabilities:Current:TheCompany:NetSalary       -310.00 EUR
    Assets:MyBank:Checking                          310.00 EUR

Second, plugin inserts 30 or 31 transactions from 2016-05-01 to 2016-05-31 like this:

2016-05-xx * "The Company" "Simplest salary entry (Generated by interpolate-spread)" #spread
    Income:TheCompany:NetSalary                     -10.00 EUR
    Liabilities:Current:TheCompany:NetSalary         10.00 EUR

Split

Problem

In fact, the argumentation is the same as in spread, but the only difference is that different usecases needs a bit different treatment. For example, our John want to set aside money for savings daily. To account for it nicely, spread won't do - we don't need any Liabilities:Current:... accounts generated for us. A simple duplication will do here.

How to use

plugin "beancount-interpolate.split" "{
    'aliases_after': ['splitAfter', 'split'],
    'default_period': 'Month',
    'default_method': 'SL',
    'min_value': 0.05,
    'max_new_tx': 9999,
    'suffix': ' (split %d/%d)',
    'tag': 'splitted'
}"

Add meta or tags to your transactions. All folllowing transactions does the same.

; Explicit.
2016-01-01 * "Me" "Set aside money for savings"
    split: "Year"
    Assets:MyBank:Checking          -365.00 EUR
    Assets:MyBank:Savings            365.00 EUR

; In fact, original date doesn't matter here, as original entry will be deleted.
2016-06-15 * "Me" "Set aside money for savings"
    splitAfter: "Year @ 2016-01-01"
    Assets:MyBank:Checking          -365.00 EUR
    Assets:MyBank:Savings            365.00 EUR


; Use can also use tags.
2016-01-01 * "Me" "Set aside money for savings" #split
    Assets:MyBank:Checking          -365.00 EUR
    Assets:MyBank:Savings            365.00 EUR

What happens

First, plugin deletes the original transaction.

Second, plugin inserts transactions every day until today, included.

2016-01-01 * "Me" "Set aside money for savings (Generated by interpolate-split)" #split
    Assets:MyBank:Checking            -1.00 EUR
    Assets:MyBank:Savings              1.00 EUR

2016-01-02 * "Me" "Set aside money for savings (Generated by interpolate-split)" #split
    Assets:MyBank:Checking            -1.00 EUR
    Assets:MyBank:Savings              1.00 EUR

...