**dict reference information** http://www.tcl.tk/man/tcl/TclCmd/dict.htm Command for manipulating [dictionary] values introduced in Tcl 8.5. See [Changes in Tcl/Tk 8.5] for links to the exact [TIP]s that specify this command. : [dict append] : [dict create] : [dict exists] : [dict filter] : [dict for] : [dict get] : [dict incr] : [dict info] : [dict keys] : [dict lappend] : [dict merge] : [dict remove] : [dict replace] : [dict set] : [dict size] : [dict unset] : [dict update] : [dict values] : [dict with] ---- **Why dict?** [LV] 2007 Dec 21 Anyone have an explanation why the data structure managed by this command is called '''dictionary'''? What is the relationship between the name and the behavior? Just curious... [Lars H]: This is what they're called in for example [PostScript], so I suppose the usage is fairly old and wide-spread. Etymologically the origin is probably the word translation dictionary as shown below, but there is also the question of where that made it into the realm of computer science. [LV] Thanks. Knowing that it is the name used in other languages helps. When I hear people refer to a [Tcl] [array] as a [hash], I wonder where the references come from and why. [Lars H]: Perhaps [Perl]? Basically, a ''dictionary'' corresponds to the set-theoretic function concept: The domain is the set of keys, and to each key is assigned exactly one value, period. A ''hash'' is a data structure that can be used to efficiently implement dictionaries, but there are alternatives such as balanced trees and [skiplist]s. ---- **Simple example using dict** Example dictionary value (English-French): % set e_f [dict create dog chien cat chat cow vache horse cheval] horse cheval cat chat cow vache dog chien Note: no ordering. [LV] Is the ''no ordering'' comment still true? [Lars H]: Not since Tue Nov 20 20:43:11 2007 UTC (revision 1.53 of tclDictObj.c, which is one past 8.5b3!). Quoting the changes entry: ''[dkf]'': ''Changed the underlying implementation of the hash table used in dictionaries to additionally keep all entries in the hash table in a linked list, which is only ever added to at the end. This makes iteration over all entries in the dictionary in key insertion order a trivial operation, and so cleans up a great deal of complexity relating to dictionary representation and stability of iteration order.'' This change makes the string representations of pure dicts ''more'' sensitive to the way the dictionary was created than they used to be, but the dependency was always there. [DKF]: Technically, sort of. No more so than with lists. What it does do is eliminate the fact that certain sequences of operations previously could (without changing the final mapping from the initial mapping) cause the reordering of all elements in the dictionary. Basically, the sequence of operations was to add dummy mappings until the backing hash was rebuilt, causing the allocation of mapping entries differently to the hash table buckets. Strip out the dummy mappings then to get back the "original" dict, except now with the elements in a different order. Moreover the representation of a dict with a new mapping added to it would probably be different if you started with a dict that had gone through this process than if you had not. To summarize, the old dict code's iteration order (which was the natural iteration order of the underlying Tcl_HashTable) was unstable and exposed far too much information about the history of the dictionary value. The new dict's stable iteration order depends only on the order in which new keys are inserted and old keys removed, and could be modeled (inefficiently) using lists or strings; its behaviour requires no understanding of the implementation to explain. [LV] so the above example becomes, in Tcl 8.5: Example dictionary value (English-French): % set e_f [dict create dog chien cat chat cow vache horse cheval] dog chien cat chat cow vache horse cheval ---- **dict for Tcl 8.4** If you want dict support in Tcl 8.4, download and compile http://pascal.scheffers.net/software/tclDict-8.5.2.tar.gz (Windows binary [http://pascal.scheffers.net/stan/dict/dict-8.5.2-win32.zip]). Version 8.5.3 of this extension is available from the [Tcl Extension Archive] (teapot) [http://teapot.activestate.com/entity/name/dict/ver/8.5.3/index]. ---- **Request for more examples** Would someone consider adding some examples here that show how using dict makes for cleaner code, etc.? It is still not clear how to determine when to use a dict, nor how to use them correctly and safely. ---- **More examples** [pcm]: Here is a useful example: an array of dicts. array set U { tom { Name "Tom Brown" Sex M Age 19 Class {4 5} } mary { Name "Mary Brown" Sex F Age 16 Class {5} } sam { Name "Sam Spade" Sex M Age 19 Class {3 4} } } dict set U(tom) Sex F dict append U(sam) Name " Jr" dict lappend U(sam) Class 5 dict incr U(mary) Age dict set U(tom) Sax Y; # Creates a new key. dict set U(bill) Sax N; # Creates a new entry. parray U ---- **Original dict implementation** What: dict Where: http://home.earthlink.net/~m-patton/dict-0.01.tar.gz http://purl.org/tcl/tip/111.html Description: Tcl implementation of TIP 111 - a new Tcl data type called dictionary, which consists of an array of values and manipulators of those values. Currently at version 0.1 . Updated: 12/2002 Contact: See web site ---- **Dictionaries and Arrays** The result of [array get] and the argument expected by [array set] are in the same format as a dict, so you can naturally switch between them: set myDict [array get myArray] dict set myDict foo bar bob $newValue array set myArray $myDict [RHS] was doing some coding for the Language Shootout, and implemented the nsieve test using both arrays and dicts. Results can be found on the [Dict vs Array Speed] page ---- **Stubs version of dict for Tcl 8.4** ''[PS] 14Apr2004'' (updated 12May2004) After a bit of chatting on the chat between dgp, dkf and myself, I have created a stubs package version of [dict] for tcl-8.4. You can download it from http://pascal.scheffers.net/software/tclDict-8.5.2.tar.gz also see [http://pascal.scheffers.net/software/] Status: * Builds, installs, passes all tests on SuSE/Linux 9.0 and Windows (MingW) * Has an extension stubs table (untested), public C API exported. * Needs more testing The package will only load in tcl-8.4.x, it uses features first introduced in Tcl-8.4. I have no idea what it would take to make it work in 8.3. It will gracefully not load in tcl-8.5+, and not raise an error. Update 18Nov2005: I have updated the tclDict code, by syncing it with Tcl8.5 CVS. The 8.5.2 Url above is the new version. This version behaves just like the real thing, except for bignum support by [[dict incr]], which I regressed to wide int support from the previous version of tclDict. A [Microsoft Windows] binary version can be downloaded from http://pascal.scheffers.net/stan/dict/dict-8.5.2-win32.zip. The dict extension is being maintained in my subversion archive at http://svn.scheffers.net/misc - Pascal. ---- I tried installing this ... but get the following error: ./configure --with-tcl=/usr/local/lib/tcl8.4 --with-tclinclude=/usr/local/include/tcl8.4 .................. skip some stuff .................... checking for Tcl public headers... /usr/local/include/tcl8.4 checking for building with threads... no (default) checking how to build libraries... shared checking if 64bit support is enabled... no checking if 64bit Sparc VIS support is requested... no checking system version (for dynamic loading)... ./configure: line 9892: syntax error near unexpected token `(' ./configure: line 9892: ` case `(ac_space=' '; set | grep ac_space) 2>&1` in' (/tmp/tclDict-8.5.2)-> uname -sr FreeBSD 5.4-RELEASE-p16 i'll keep checking here for any help. this is using tclDict-8.5.2.tar.gz (it says use that for tcl 8.4...) ''([NEM]: Is this comment still in need of answering? See also [comp.lang.tcl] for general questions.)'' [MJ] - It seems it is. This is caused by tclDict using an outdated tcl.m4 which has a quoting issue with [bash]. The tcl.m4 (and generated configure) in the download should be fixed. ---- **Anyone considered dict equal?** [LV] Has anyone considered either submitting a [TIP] for a '''dict equal''' command or at least writing up a first draft of the script for [tcllib]? It would have to have a '''callback''-ish type feature, ala [lsort], because you couldn't know, in general, whether two things are "equal" or not... [NEM]: Such a command is not too hard to write, see [dictutils] for one implementation. Note that a general scheme for equality of arbitrary data structures is quite tricky to write. See [unification] for one approach. ---- [NEM] ''12 Feb 2007'': Moved lots of discussion on the design of dict to [dict discussion] in an attempt to focus this page more on the actual uses and techniques for working with dicts. Apologies if I moved too much by mistake. ---- **Care needed when extracting a dict from a list** [LV] 2007 Oct 17 [RS] wrote on comp.lang.tcl the following helpful advice: Be careful with the argument "args" - that is a list. If you pass one dict in args, retrieve it with: set dict [lindex $args 0] Because dicts always need an even number of key value key value.. ---- **dict vs TclX's key list?** [LV] Has anyone compared [TclX]'s '''key list''' commands to ''dict'' to see how much of the functionality of a key list is missing if one were to try to use a dict in place of a TclX key list? [Lars H]: This might be a subject for the [Complex data structures] page. ---- **Shimmering between dict and list** [AMG]: I wonder if shimmering between dict and list can be minimized by unifying their [Tcl_Obj] internal data structures. Just add a Tcl_HashTable pointer to struct List, and get rid of struct Dict. If the Tcl_HashTable pointer is NULL, a dict representation doesn't currently exist for the list. If the pointer isn't NULL, it points to a hash table that indexes the list. Dict operations performed on a list Tcl_Obj will use the Tcl_HashTable, creating it if it doesn't already exist. Read-only list operations leave the Tcl_HashTable untouched. Destructive list operations set the Tcl_HashTable pointer to NULL. (Or maybe they only do this when changing an even-numbered, i.e. key, element.) struct List and struct Dict are Tcl internals, so (as far as I know) this change can be made without breaking compatibility. This would be very useful to me in [Wibble] for creating dict-like objects with potential (but rare) key duplication. [[[lappend]]] is used to make the data structure. If duplicate elements need to be kept separate, ordinary list operations are used to extract the data. If duplicate elements don't exist or can be ignored (the common case), dict operations are used instead, and the first such operation automatically creates the hash table. Actually this mode of operation is currently available, but the hash table would be regenerated every time a dict operation is performed. Hmm, would epoch and chain also need to be imported into struct List? If so, instead of directly putting a Tcl_HashTable pointer into struct List, I would instead use a struct Dict pointer, to avoid growing struct List more than necessary. struct Dict would have everything removed that's already present in struct List, so it would be reduced to table, epoch, and chain. ---- Anyone knowlegable enough about dicts to add details to [http://en.wikipedia.org/wiki/Comparison_of_programming_languages_(mapping)#Tcl]? ---- **See also:** * [dict tips and tricks] * [dictutils] for a collection of dict-related utilities. * [forward-compatible dict] * [dictn] * [dict in snit] * [dictionaries as arrays] * [dictionaries as arrays by Stubs] * [everything is a dict] * [dict probe] * [pdict: Pretty print a dict] * [dict vs array speed] <>Category Command | Category Package | Category Data Structure