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;doc: journal: clarify that it's the first-seen digit group style

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Simon Michael 2020-11-10 09:29:04 -08:00
parent 8bdb28a991
commit 70f95e9f2c
2 changed files with 29 additions and 15 deletions
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5
hledger-lib/Hledger/Data/Journal.hs
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@ -1010,7 +1010,10 @@ commodityStylesFromAmounts amts =
-- Though, we don't have the info for a good error message, so maybe elsewhere.
-- | Given a list of amount styles (assumed to be from parsed amounts
-- in a single commodity), in parse order, choose a canonical style.
-- Traditionally it's "the style of the first, with the maximum precision of all".
-- This is:
-- the general style of the first amount,
-- with the first digit group style seen,
-- with the maximum precision of all.
--
canonicalStyleFrom :: [AmountStyle] -> AmountStyle
canonicalStyleFrom [] = amountstyle

39
hledger-lib/hledger_journal.m4.md
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@ -481,33 +481,44 @@ commodity 1 000 000.9455
### Commodity display style
For each commodity, hledger chooses a consistent format to use when
For each commodity, hledger chooses a consistent style to use when
displaying amounts. (Except [price amounts](#prices), which are always
displayed as written). The display style is chosen as follows:
- If there is a [commodity directive](#declaring-commodities) (or
[default commodity directive](#default-commodity)) for the
commodity, that format is used (see examples above).
commodity, its style is used (see examples above).
- Otherwise the format of the first posting amount in that commodity
seen in the journal is used.
But the number of decimal places ("precision") will be the maximum
from all posting amounts in that commodity.
- Otherwise the style is inferred from the amounts in that commodity
seen in the journal.
- Or if there are no such amounts in the journal, a default format is
- Or if there are no such amounts in the journal, a default style is
used (like `$1000.00`).
Transaction prices don't affect the amount display style directly, but
occasionally they can do so indirectly (eg when an posting's amount is
A style is inferred from the journal amounts in a commodity as follows:
- Use the general style (decimal mark, symbol placement) of the first amount
- Use the first-seen digit group style (digit group mark, digit group sizes), if any
- Use the maximum number of decimal places of all.
Transaction price amounts don't affect the commodity display style directly,
but occasionally they can do so indirectly (eg when a posting's amount is
inferred using a transaction price). If you find this causing
problems, use a commodity directive to fix the display style.
In summary: amounts will be displayed much as they appear in your
journal, with the max observed number of decimal places. If you want
to see fewer decimal places in reports, use a
[commodity directive](#declaring-commodities)
to override that.
In summary, each commodity's amounts will be normalised to
- the style declared by a `commodity` directive
- or, the style of the first posting amount in the journal,
with the first-seen digit group style and the maximum-seen number of decimal places.
If reports are showing amounts in a way you don't like (eg, with too many decimal places),
use a [commodity directive](#declaring-commodities) to set your preferred style.
### Rounding
Amounts are stored internally as decimal numbers with up to 255 decimal places,
and displayed with the number of decimal places specified by the commodity display style.
Note, hledger uses [banker's rounding](https://en.wikipedia.org/wiki/Bankers_rounding):
it rounds to the nearest even number, eg 0.5 displayed with zero decimal places is "0").
(Guaranteed since hledger 1.17.1; in older versions this could vary if hledger was built with Decimal < 0.5.1.)