Totaling sub-postings with ledger-mode

[Ben Hancock]

Hi folks,

This is a question about using ledger-mode within Emacs. I use Ledger
with virtual accounts for envelope-style budgeting. At the beginning of
the month, I'll typically make an entry that looks something like this:

2020-07-01 * Budget: July 2020
[Budget:Food] $100.00
[Budget:Gas] $25.00
[Budget:Books] $25.00
[Assets:Checking] -$150.00

Now, the mental math in the above example is easy enough, but
unfortunately my real budget is typically more complex. I'm aware that I
can elide the bottom posting, but I find its helpful to see how much I'm
actually budgeting as I make my allocations for the month.

Is there a handy function available within ledger-mode to total up all
the "Budget" postings and insert the correct inverse amount for the
posting at bottom? I've checked the docs but not found anything (or have
overlooked the relevant section). I've also tried
"ledger-post-edit-amount" -- bound to "C-c C-b" -- and while this pops
open calc to let /me/ do the math, I'd love for the calculation to be
done for me.

Thanks!

--
Ben Hancock
b...@benghancock.com
https://benghancock.github.io