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  4. dict(n)

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dict(n) Tcl Built-In Commands dict(n) 





NAME


dict - Manipulate dictionaries






SYNOPSIS


dict option arg ?arg ...?








DESCRIPTION


Performs one of several operations on dictionary values or
    variables containing dictionary values (see the DICTIONARY VALUES
    section below for a description), depending on option. The legal
    options (which may be abbreviated) are:



  

  
This appends the given string (or strings) to the value that the given key
      maps to in the dictionary value contained in the given variable, writing
      the resulting dictionary value back to that variable. Non-existent keys
      are treated as if they map to an empty string.

  

  
Create a new dictionary that contains each of the key/value mappings
      listed as arguments (keys and values alternating, with each key being
      followed by its associated value.)

  

  
This returns a boolean value indicating whether the given key (or path of
      keys through a set of nested dictionaries) exists in the given dictionary
      value. This returns a true value exactly when dict get on
      that path will succeed.

  

  
This takes a dictionary value and returns a new dictionary that contains
      just those key/value pairs that match the specified filter type (which may
      be abbreviated.) Supported filter types are:







  

  
The key rule only matches those key/value pairs whose keys match the given
      pattern (in the style of string match.)

  

  
The script rule tests for matching by assigning the key to the
      keyVar and the value to the valueVar, and then evaluating
      the given script which should return a boolean value (with the key/value
      pair only being included in the result of the dict filter
      when a true value is returned.) Note that the first argument after the
      rule selection word is a two-element list. If the script returns
      with a condition of TCL_BREAK, no further key/value pairs are
      considered for inclusion in the resulting dictionary, and a condition of
      TCL_CONTINUE is equivalent to a false result. The key/value pairs
      are tested in the order in which the keys were inserted into the
      dictionary.

  

  
The value rule only matches those key/value pairs whose values match the
      given pattern (in the style of string match.)







  

  
This command takes three arguments, the first a two-element list of
      variable names (for the key and value respectively of each mapping in the
      dictionary), the second the dictionary value to iterate across, and the
      third a script to be evaluated for each mapping with the key and value
      variables set appropriately (in the manner of foreach.) The result
      of the command is an empty string. If any evaluation of the body generates
      a TCL_BREAK result, no further pairs from the dictionary will be
      iterated over and the dict for command will terminate successfully
      immediately. If any evaluation of the body generates a TCL_CONTINUE
      result, this shall be treated exactly like a normal TCL_OK result.
      The order of iteration is the order in which the keys were inserted into
      the dictionary.

  

  
Given a dictionary value (first argument) and a key (second argument),
      this will retrieve the value for that key. Where several keys are
      supplied, the behaviour of the command shall be as if the result of
      dict get $dictVal $key was passed as the first argument to dict
      get with the remaining arguments as second (and possibly subsequent)
      arguments. This facilitates lookups in nested dictionaries. For example,
      the following two commands are equivalent:










dict get $dict foo bar spong
dict get [dict get [dict get $dict foo] bar] spong




If no keys are provided, dict get will return a list
    containing pairs of elements in a manner similar to array get. That
    is, the first element of each pair would be the key and the second element
    would be the value for that key.


It is an error to attempt to retrieve a value for a key that is
    not present in the dictionary.





  

  
This adds the given increment value (an integer that defaults to 1 if not
      specified) to the value that the given key maps to in the dictionary value
      contained in the given variable, writing the resulting dictionary value
      back to that variable. Non-existent keys are treated as if they map to 0.
      It is an error to increment a value for an existing key if that value is
      not an integer.

  

  
This returns information (intended for display to people) about the given
      dictionary though the format of this data is dependent on the
      implementation of the dictionary. For dictionaries that are implemented by
      hash tables, it is expected that this will return the string produced by
      Tcl_HashStats, similar to array statistics.

  

  
Return a list of all keys in the given dictionary value. If a pattern is
      supplied, only those keys that match it (according to the rules of
      string match) will be returned. The returned keys will be in the
      order that they were inserted into the dictionary.

  

  
This appends the given items to the list value that the given key maps to
      in the dictionary value contained in the given variable, writing the
      resulting dictionary value back to that variable. Non-existent keys are
      treated as if they map to an empty list, and it is legal for there to be
      no items to append to the list. It is an error for the value that the key
      maps to to not be representable as a list.

  

  
Return a dictionary that contains the contents of each of the
      dictionaryValue arguments. Where two (or more) dictionaries contain
      a mapping for the same key, the resulting dictionary maps that key to the
      value according to the last dictionary on the command line containing a
      mapping for that key.

  

  
Return a new dictionary that is a copy of an old one passed in as first
      argument except without mappings for each of the keys listed. It is legal
      for there to be no keys to remove, and it also legal for any of the keys
      to be removed to not be present in the input dictionary in the first
      place.

  

  
Return a new dictionary that is a copy of an old one passed in as first
      argument except with some values different or some extra key/value pairs
      added. It is legal for this command to be called with no key/value pairs,
      but illegal for this command to be called with a key but no value.

  

  
This operation takes the name of a variable containing a dictionary value
      and places an updated dictionary value in that variable containing a
      mapping from the given key to the given value. When multiple keys are
      present, this operation creates or updates a chain of nested
    dictionaries.

  

  
Return the number of key/value mappings in the given dictionary
    value.

  

  
This operation (the companion to dict set) takes the name of a
      variable containing a dictionary value and places an updated dictionary
      value in that variable that does not contain a mapping for the given key.
      Where multiple keys are present, this describes a path through nested
      dictionaries to the mapping to remove. At least one key must be specified,
      but the last key on the key-path need not exist. All other components on
      the path must exist.

  

  
Execute the Tcl script in body with the value for each key
      (as found by reading the dictionary value in dictionaryVariable)
      mapped to the variable varName. There may be multiple
      key/varName pairs. If a key does not have a mapping,
      that corresponds to an unset varName. When body terminates,
      any changes made to the varNames is reflected back to the
      dictionary within dictionaryVariable (unless
      dictionaryVariable itself becomes unreadable, when all updates are
      silently discarded), even if the result of body is an error or some
      other kind of exceptional exit. The result of dict update is
      (unless some kind of error occurs) the result of the evaluation of
      body.






Each varName is mapped in the scope enclosing the dict
    update; it is recommended that this command only be used in a local
    scope (procedure or lambda term for apply). Because of this,
    the variables set by dict update will continue to exist after the
    command finishes (unless explicitly unset). Note that the mapping of
    values to variables does not use traces; changes to the
    dictionaryVariable's contents only happen when body
    terminates.





  

  
Return a list of all values in the given dictionary value. If a pattern is
      supplied, only those values that match it (according to the rules of
      string match) will be returned. The returned values will be in the
      order of that the keys associated with those values were inserted into the
      dictionary.

  

  
Execute the Tcl script in body with the value for each key in
      dictionaryVariable mapped (in a manner similarly to dict
      update) to a variable with the same name. Where one or more
      keys are available, these indicate a chain of nested dictionaries,
      with the innermost dictionary being the one opened out for the execution
      of body. As with dict update, making
      dictionaryVariable unreadable will make the updates to the
      dictionary be discarded, and this also happens if the contents of
      dictionaryVariable are adjusted so that the chain of dictionaries
      no longer exists. The result of dict with is (unless some kind of
      error occurs) the result of the evaluation of body.






The variables are mapped in the scope enclosing the dict
    with; it is recommended that this command only be used in a local scope
    (procedure or lambda term for apply). Because of this, the
    variables set by dict with will continue to exist after the command
    finishes (unless explicitly unset). Note that the mapping of values
    to variables does not use traces; changes to the dictionaryVariable's
    contents only happen when body terminates.


If the dictionaryVariable contains a value that is not a
    dictionary at the point when the body terminates (which can easily
    happen if the name is the same as any of the keys in dictionary) then an
    error occurs at that point. This command is thus not recommended for use
    when the keys in the dictionary are expected to clash with the
    dictionaryVariable name itself. Where the contained key does map to a
    dictionary, the net effect is to combine that inner dictionary into the
    outer dictionary; see the EXAMPLES below for an illustration of
  this.








DICTIONARY VALUES


Dictionaries are values that contain an efficient,
    order-preserving mapping from arbitrary keys to arbitrary values. Each key
    in the dictionary maps to a single value. They have a textual format that is
    exactly that of any list with an even number of elements, with each mapping
    in the dictionary being represented as two items in the list. When a command
    takes a dictionary and produces a new dictionary based on it (either
    returning it or writing it back into the variable that the starting
    dictionary was read from) the new dictionary will have the same order of
    keys, modulo any deleted keys and with new keys added on to the end. When a
    string is interpreted as a dictionary and it would otherwise have duplicate
    keys, only the last value for a particular key is used; the others are
    ignored, meaning that, “apple banana” and “apple carrot
    apple banana” are equivalent dictionaries (with different string
    representations).


Operations that derive a new dictionary from an old one (e.g.,
    updates like dict set and dict unset) preserve the order of
    keys in the dictionary. The exceptions to this are for any new keys they
    add, which are appended to the sequence, and any keys that are removed,
    which are excised from the order.






EXAMPLES


Basic dictionary usage:






# Make a dictionary to map extensions to descriptions
set filetypes [dict create .txt "Text File" .tcl "Tcl File"]
# Add/update the dictionary
dict set filetypes .tcl "Tcl Script"
dict set filetypes .tm  "Tcl Module"
dict set filetypes .gif "GIF Image"
dict set filetypes .png "PNG Image"
# Simple read from the dictionary
set ext ".tcl"
set desc [dict get $filetypes $ext]
puts "$ext is for a $desc"
# Somewhat more complex, with existence test
foreach filename [glob *] {


    set ext [file extension $filename]


    if {[dict exists $filetypes $ext]} {


        puts "$filename is a [dict get $filetypes $ext]"


    }
}




Constructing and using nested dictionaries:






# Data for one employee
dict set employeeInfo 12345-A forenames "Joe"
dict set employeeInfo 12345-A surname   "Schmoe"
dict set employeeInfo 12345-A street "147 Short Street"
dict set employeeInfo 12345-A city   "Springfield"
dict set employeeInfo 12345-A phone  "555-1234"
# Data for another employee
dict set employeeInfo 98372-J forenames "Anne"
dict set employeeInfo 98372-J surname   "Other"
dict set employeeInfo 98372-J street "32995 Oakdale Way"
dict set employeeInfo 98372-J city   "Springfield"
dict set employeeInfo 98372-J phone  "555-8765"
# The above data probably ought to come from a database...
# Print out some employee info
set i 0
puts "There are [dict size $employeeInfo] employees"
dict for {id info} $employeeInfo {


   puts "Employee #[incr i]: $id"


   dict with info {


      puts "   Name: $forenames $surname"


      puts "   Address: $street, $city"


      puts "   Telephone: $phone"


   }
}
# Another way to iterate and pick out names...
foreach id [dict keys $employeeInfo] {


   puts "Hello, [dict get $employeeInfo $id forenames]!"
}




A localizable version of string toupper:






# Set up the basic C locale
set capital [dict create C [dict create]]
foreach c [split {abcdefghijklmnopqrstuvwxyz} ""] {


   dict set capital C $c [string toupper $c]
}
# English locales can luckily share the "C" locale
dict set capital en [dict get $capital C]
dict set capital en_US [dict get $capital C]
dict set capital en_GB [dict get $capital C]
# ... and so on for other supported languages ...
# Now get the mapping for the current locale and use it.
set upperCaseMap [dict get $capital $env(LANG)]
set upperCase [string map $upperCaseMap $string]




Showing the detail of dict with:






proc sumDictionary {varName} {


   upvar 1 $varName vbl


   foreach key [dict keys $vbl] {


      # Manufacture an entry in the subdictionary


      dict set vbl $key total 0


      # Add the values and remove the old


      dict with vbl $key {


         set total [expr {$x + $y + $z}]


         unset x y z


      }


   }


   puts "last total was $total, for key $key"
}
set myDict {


   a {x 1 y 2 z 3}


   b {x 6 y 5 z 4}
}
sumDictionary myDict
#    prints: last total was 15, for key b
puts "dictionary is now \"$myDict\""
#    prints: dictionary is now "a {total 6} b {total 15}"




When dict with is used with a key that clashes with the
    name of the dictionary variable:






set foo {foo {a b} bar 2 baz 3}
dict with foo {}
puts $foo
#    prints: a b foo {a b} bar 2 baz 3








SEE ALSO


append(n), array(n), foreach(n), incr(n), list(n), lappend(n),
    set(n)






KEYWORDS


dictionary, create, update, lookup, iterate, filter







  

    8.5
    Tcl