register: --average implies --empty

The -A flag now enables -E, so that with a report interval the averages
are always per-period and not per-report-line. (Without a report
interval, -E is already the default).

doc/MANUAL.md

@@ -751,17 +751,9 @@ The `--depth` option limits the amount of sub-account detail displayed:
 
     $ hledger register assets:bank:checking --depth 2
 
-With a [reporting interval](#reporting-interval) it shows aggregated
+The `--average`/`-A` flag shows the running average posting amount
-summary postings within each interval:
+instead of the running total (so, the final number displayed is the
-
+average for the whole report period). This flag implies `--empty` (see below).
-    $ hledger register --monthly rent
-    $ hledger register --monthly -E food --depth 4
-
-Note that the report start/end dates will be "enlarged" in this case
-so that they encompass the displayed intervals. This is so that the
-first and last intervals will be "full" and comparable to the others.
-
-The `--average`/`-A` flag shows the running average posting amount instead of the running total.
 
 The `--related`/`-r` flag shows the *other* postings in the transactions
 of the postings which would normally be shown.
@@ -772,6 +764,22 @@ names, use `-w` to increase the width to 120 characters, or `-wN` to set
 any desired width (at least 50 recommended).
 Note, currently -w/--width can not have a space between flag and value ([#149](https://github.com/simonmichael/hledger/issues/149)).
 
+With a [reporting interval](#reporting-interval) register shows
+aggregated summary postings, within each interval:
+
+    $ hledger register --monthly rent
+    $ hledger register --monthly -E food --depth 4
+
+One summary posting will be shown for each account in each interval.
+Summary postings with a zero amount are not shown; use the `--empty`/`-E` flag to show them.
+
+If necessary, use the `--depth` option to summarise the accounts.
+It's often most useful to see just one line per interval.
+
+When using report intervals, the report's normal start/end dates are
+"enlarged" to contain a whole number of intervals, so that the first
+and last intervals will be "full" and comparable to the others.
+
 #### balance
 
 The balance command displays accounts and their balances.

hledger-lib/Hledger/Reports/PostingsReport.hs

@@ -71,13 +71,13 @@ postingsReport opts q j = (totallabel, items)
                       journalPostings $ journalSelectingAmountFromOpts opts j
       (precedingps, reportps) = dbg "precedingps, reportps" $ span (beforestartq `matchesPosting`) pstoend
 
-      empty = queryEmpty q
+      showempty = queryEmpty q || average_ opts
       -- displayexpr = display_ opts  -- XXX
       interval = intervalFromOpts opts -- XXX
 
       whichdate = whichDateFromOpts opts
       itemps | interval == NoInterval = reportps
-             | otherwise              = summarisePostingsByInterval interval whichdate depth empty reportspan reportps
+             | otherwise              = summarisePostingsByInterval interval whichdate depth showempty reportspan reportps
       items = postingsReportItems itemps nullposting whichdate depth startbal runningcalc 1
         where
           startbal = if balancetype_ opts == HistoricalBalance then sumPostings precedingps else 0
@@ -117,9 +117,9 @@ mkpostingsReportItem showdate showdesc wd p b = (if showdate then Just date else
 -- are one per account per interval and aggregated to the specified depth
 -- if any.
 summarisePostingsByInterval :: Interval -> WhichDate -> Int -> Bool -> DateSpan -> [Posting] -> [Posting]
-summarisePostingsByInterval interval wd depth empty reportspan ps = concatMap summarisespan $ splitSpan interval reportspan
+summarisePostingsByInterval interval wd depth showempty reportspan ps = concatMap summarisespan $ splitSpan interval reportspan
     where
-      summarisespan s = summarisePostingsInDateSpan s wd depth empty (postingsinspan s)
+      summarisespan s = summarisePostingsInDateSpan s wd depth showempty (postingsinspan s)
       postingsinspan s = filter (isPostingInDateSpan' wd s) ps
 
 tests_summarisePostingsByInterval = [

hledger/Hledger/Cli/Register.hs

@@ -29,7 +29,7 @@ registermode = (defCommandMode $ ["register"] ++ aliases) {
  ,modeGroupFlags = Group {
      groupUnnamed = [
       flagNone ["historical","H"] (\opts -> setboolopt "historical" opts) "include prior postings in the running total"
-     ,flagNone ["average","A"] (\opts -> setboolopt "average" opts) "show a running average instead of the running total"
+     ,flagNone ["average","A"] (\opts -> setboolopt "average" opts) "show a running average instead of the running total (implies --empty)"
      ,flagNone ["related","r"] (\opts -> setboolopt "related" opts) "show postings' siblings instead"
      ,flagReq  ["width","w"] (\s opts -> Right $ setopt "width" s opts) "N" "set output width (default: 80)"
      ]