<xtree [XTREE=$treename] $command [$values] [$treename][ /]>
<xtree [XTREE=$treename] [options] $command [$values] [$treename]>
<xtree> function is a fast way to maintain a sorted list of
string values in memory - faster than using a SQL table. Values can
be added, removed, counted and deleted from a tree, named with
treename (default tree name is empty). The values
parameter is the list of values to operate on, for
SET it is the option(s) to
set. Otherwise the values parameter is not given, or is empty
if treename is specified via the last-argument syntax.
Each value in an xtree has a count and a sequence number associated
with it. The count is the number of times the value was inserted.
The sequence number is the order in which the value was first
inserted, starting with 0 for the first value inserted. These values
are retrieved either with the
SEQ commands, or
in the ret.count and ret.seq variables.
If no options (or only
XTREE option) are given to
<xtree>, it returns values in ret as a simple function.
If any of the options below are given (except
<xtree> is a looping statement, e.g. a closing "</xtree>"
tag is expected, and ret.count/ret.seq are set (and
looped over) as well.
The variables ret.count and ret.seq, when set, are the
corresponding count and sequence numbers for ret.
<xtree> is a looping statement, loop/next
are set as in
SQL (loop always starts at 0). Any
statements inside the block are executed once per returned value, with
ret being a loop variable accumulating values. The loop can
be exited with
RETURN. The loop syntax was
added in version 2.6.938200000 19990924.
SQL, do not accumulate hits in
ret/ret.count/ret.seq, and do not make them
loop variables; each new value erases the previous.
should be used in a looping
<xtree> when a large number of
return values are expected but only need to be examined one at a
time; this saves memory and time since all the values do not have
to be stored in memory.
ROW should also be used when
functions are called within the block, because otherwise
ret is a loop variable, hindering multi-value returns
(see --warn-if-ret-loop, here).
ROW should also be used when the
commands are not to be used, as it saves the memory of preserving
those values for a later
SKIP=$nSkip the first
$nvalues. This does not affect the value of loop.
MAX=$nReturn at most
XTREE=$treenameUse tree named treename instead of the default. This option was added in version 5.01.1217380000 20080729. The old syntax was to give the tree name as the last argument, with no option name, which can be confusing. Only one syntax -
XTREEoption or last-unnamed-argument - may be used in a statement.
$command argument determines what
whether it takes a values argument or not, and what values, if
any, are returned. It is one of the following commands:
CLEARClear the tree. All counts are set to 0, but the tree and its values remain in memory. values need not be set. No values are returned.
DUMPDump the tree. The return value ret is a unique, sorted list of the values in the tree that have non-zero counts, in ascending order. In the looping syntax, ret.count and ret.seq are set to the corresponding count and sequence numbers; in the non-looping syntax for version 7 and earlier, these values must be retrieved with separate
SEQcommands afterwards. If the
CLEARoption (not command) is set with
SET, each value is also cleared as it is returned. values need not be set.
COUNTDump the value counts from the immediately previous non-looping
INSERTcommand on the same tree. ret will contain a list of the number of times each value from the operation occurs in the tree. For the looping syntax, nothing is returned - the counts and sequences are available during the
INSERTin ret.count and ret.seq. values need not be set.
SEQReturns the corresponding sequence numbers (starting at 0), from the immediately previous non-looping
INSERTon the same tree. These indicate the order in which the strings were originally added. For the looping syntax, nothing is returned - the counts and sequences are available during the
INSERTin ret.count and ret.seq. values need not be set.
INSERTAdds the values to the tree, if not already present, and increment their counts. If the
NOADDoption is set (below), new values are not added; only already-present values are incremented. In versions after 3.01.963400000 20000712, the inserted values - and counts and sequence numbers, if looping - are returned. This saves an extra
SEARCHto determine the numbers right after an
DELETEDeletes the values from the tree, i.e. sets their counts to 0. No values are returned in ret.
SEARCHReturns a list of the values that are in the tree. Counts and sequences are available as per
Set the option(s) given in values. In version 6.00.1305253000 20110512 and later, 1 is returned on success, 0 on failure; previous versions always returned empty string. Looping version iterates 0 times in version 7 and earlier. Options:
Do not add new values to the tree during an
Inserting a previously-cleared value will make it
"reappear", because it was present before but now has a
non-zero count. But wholly-new values will not be inserted.
clearAlso clear the tree during a
stringcomparemode $modeSet string compare mode - how values are compared - for the tree to
$mode. The syntax is the same as the
stringcomparemode(here). The default (and the meaning of values
builtin) is the current
stringcomparemode. This option must be set before any data is inserted into the tree, as it would alter the sort order. Added in version 6.
storefolded $onOffSet the store-folded flag for the tree to
$onOff(i.e. "on" or "off"). Enabling store-folded increases speed slightly, at the expense of not retaining inserted values exactly.
storefolded is on, values are folded (according to
stringcomparemode) once, at insert time, and stored
folded. This increases speed because only one folding is
needed. However, values returned from
DUMP etc. will
be the folded value, not the originally-inserted value.
stringcomparemode is set to
the inserted value "
McDuff" will be
storefolded is off (the default), values are folded
whenever needed for comparisons, and stored exactly as
inserted. This decreases speed because potentially more than
one folding is needed. However, the originally-inserted value
is preserved, i.e. if "
McDuff" is inserted in an
ignorecase tree, it will be
In either case,
stringcomparemode is respected for
searches, inserts etc.; just the value of ret is
affected. This option must be set before any data is
inserted into the tree, as it would alter the sort order.
Added in version 6.
storefolded are off;
stringcomparemode is the
same as the
<apicp> value. Note that since the last
two settings can only be set on an empty tree, defaults can
only be fully restored on an empty tree as well. In version
6.00.1305312600 20110513 and earlier,
storefolded mode were not restored at all when
Gets the option(s) listed in values. Added in version 6.00.1305253000 20110512. Options and what they return are:
1 if not adding new values to the tree during an
0 if adding.
1 if clearing the tree during a
DUMP, 0 if not.
stringcomparemode for the tree.
1 if storing values folded, 0 if not.
The number of items in the tree, i.e. the number of non-zero
count items (returned by
DUMP). It is much faster
(constant-time) to obtain this value via
DUMPing the tree and checking loop.
The number of allocated items in the tree, i.e. including zero-count (cleared) items.
The number of bytes of memory used by the tree.
FLUSHRemove the tree and free its memory. Nothing is returned.
<xtree> function returns either nothing, a list of strings,
or a list of integer counts/sequences. If invoked as a looping command,
ret.count and ret.seq may be set as well.
<$txt = "senselessness" "this" "test" "finesse">
<rex "." $txt> <!-- split the words into letters -->
<xtree INSERT $ret>
<xtree ROW DUMP>
The output would be a count of how many times each letter occurs among all the words:
<xtree> function was added Apr. 29 1997. The loop syntax
was added in version 2.6.938200000 19990924, as was support for
full binary data.
Note that loop, next, ret.count and ret.seq are only set in the looping version.
It is not possible to modify an xtree while inside an
loop for the same tree, nor is it possible to start another
DUMP inside the loop. An error message such as "Cannot
flush xtree: still in use" or "Cannot insert into xtree while
walking it" may be generated in such cases.
In long-running scripts, trees should be
FLUSHed when done,
to save memory. Since they are kept only in memory, they will be lost
when the script exits.
ROW should be used whenever possible
to save memory and speed.
In version 6 and later, string comparisons use the current apicp stringcomparemode setting (here), changeable with the set stringcomparemode tree option.