1.  Tables using *table

The *table utility provides compact definition of data tables wherein columns names are given in the first row.

If the first element of the initialing list is a single non-alphanumeric character, it specifies the table type, otherwise the table is a simple table. The currently supported types are "*", "#" and "^".

1.1  Simple Tables

A simple table is simply a list of rows where the first element is not a single non-alphanumeric character, eg.

  *table workers {
     { First Last     Age }
     { Bob   Brown    19  }
     { Tom   Wake     18  }
     { Tommy Smart    14  }
     { Bill  Williams 17  }
  }

  $workers  update 1  Age 21;  # Update Bobs age.
  set id [$workers find -name Tom -key First]
  $workers  incr $id  Age 2

  pack [*treeview .t -tree $workers -flat 1] -fill both -expand y

Records get inserted starting from node id 1. This form of table is less useful because it lacks symbolic indexes.

1.2  Indexed Tables

If the first element in the list is "*", then it is an indexed *table. The second element contains the column titles. The rest of the list contains index/row pairs.

Programatically, rows can be indexed with a 0-> preceding the index label. Note that no real checking is performed, eg. duplicate index labels are accepted. Also new column-keys may be created by the user.

  *table staff {
     *     { First Last     Age }
     bob   { Bob   Brown    19  }
     tom   { Tom   Wake     18  }
     tom   { Tommy Smart    14  }
     bill  { Bill  Williams 17  }
  }

  $staff  set  0->bob  Last Brown-Levy
  $staff  incr 0->tom  Age  2;  # Matches 1st entry "Tom Wake"
  $staff  set  0->bill Sex  M;  # Creates the new key Sex.

  toplevel .s
  pack [*treeview .s.t -tree $staff] -fill both -expand y

1.3  Validated Indexed Tables

If the first list element is a "#" then it is a validated indexed *table.

Programatically, elements can be indexed directly with the label (because it was also added as a tag). An error will be raised if a duplicate index is inserted. Also invalid is inserting new key names.

  *table managers {
     #     { First  Last     Age }
     bob   { Bob    Brown    19  }
     tom   { Tom    Wake     18  }
     bill  { Bill   Williams 17  }
  }

  $managers  incr   bob    Age 2
  $managers  update bill   Last Barry

  catch { $managers insert end -label bob }
  # This is an error as bob is already defined.

  catch { $managers set bob   Sex M }
  # This is an error as there is no key Sex.

  toplevel .m
  pack [*treeview .m.t -tree $managers] -fill both -expand y

 }

1.4  Struct Tables

If the first list element is a "^" then it is a struct *table. This is like a validated indexed table, but uses a struct definition to obtain field names, eg:

   *struct new user {
      { First     {}  "First name of user" }
      { Last      {}  "Last name of user" }
      { Age       0   "Age of user" -type Int }
  }

  *table managers {
     ^     user
     bob   { Bob    Brown    19  }
     tom   { Tom    Wake     18  }
     bill  { Bill   Williams 17  }
  }

  $managers update bill   Last Barry

A struct provides default values for ommitted data fields. It also supports typechecking. See *struct for details.

© 2008 Peter MacDonald