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Setting up an array and sorting the elements by key
Arrays and dicts example from a Well House Consultants training course
More on Arrays and dicts [link]

This example is described in the following article(s):
   • User defined sorting and other uses of callbacks in Tcl and Tk - [link]

Source code: ar_rail Module: T208
# Setting up an array and sorting the elements by key

# 5337 FMR BN1 9PU TQ 346088 50.8621241499 -0.0873836155 Falmer 771095 838150 920259 1009988 1045586 1033392

set fh [open railstats.xyz r]

proc byquantity {a b} {
        global uses
        # Following line is useful as a demo of how sort works
        # puts "$a .... $b"
        return [expr $uses($a) - $uses($b)]

while {[set line [gets $fh]] != ""} {
        set fields [split $line "\t"]

        set placename [lindex $fields 6]
        set passengers [lindex $fields 8]

# NULL is not special in Tcl ... it just happens to be a value in
# our data file and we wish to elimitate data lines that have it in
# the passengers field

        if {$passengers != "NULL"} {
                set uses($placename) $passengers

foreach pl [lsort -command byquantity [array names uses South*]] {
        puts [format "%8d %s" $uses($pl) $pl]


# --------------- never gets past here in running
# sample results

munchkin:ta grahamellis$ tclsh ar_rail
    1942 South Bank
    6106 South Greenford
    7245 Southease
   35812 South Wigston
   42090 South Tottenham
   46146 South Hampstead
   50424 South Merton
   78239 South Milford
   80995 South Acton
  135017 Southminster
  185022 South Kenton
  200700 Southbourne
  245667 South Bermondsey
  252079 Southwick
  263038 Southbury
  265547 South Elmsall
  424306 South Gyle
  772355 South Croydon
  797470 Southend East
  859286 Southall
 1421305 Southampton Airport (Parkway)
 1582115 Southport
 1719370 Southend Victoria
 3018137 Southend Central
 4844998 Southampton Central
munchkin:ta grahamellis$
Learn about this subject
This module and example are covered on the following public courses:
 * Learning to program in Tcl
 * Tcl Programming
 * Tcl Programming
Also available on on site courses for larger groups

Books covering this topic
Yes. We have over 700 books in our library. Books covering Tcl, Tk and Expect are listed here and when you've selected a relevant book we'll link you on to Amazon to order.

Other Examples
This example comes from our "Arrays and dicts" training module. You'll find a description of the topic and some other closely related examples on the "Arrays and dicts" module index page.

Full description of the source code
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Many other training modules are available for download (for limited use) from our download centre under an Open Training Notes License.

Other resources
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This is a sample program, class demonstration or answer from a training course. It's main purpose is to provide an after-course service to customers who have attended our public private or on site courses, but the examples are made generally available under conditions described below.

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