Exercises, examples and other material relating to training module T208. This topic is presented on public courses Learning to program in Tcl, Tcl Basics

Arrays are variables that can contain a number of strings, and each one can be looked up by its index and key. Unlike arrays in other languages, array keys in Tcl are strings, not integers, and array members can contain strings of differing lengths. Dicts are an alternative to arrays that implement unordered, keyed collections through strings. You'll start this module learning about the basics of arraysi and dicts, and go on to learn some of the wider uses and extra power that's provided by their somewhat unusual specification, taught by example.

Articles and tips on this subject		updated
3582	Tcl collections - lists, dicts and array In Tcl, almost all variables are what is described as "pure" - which means that they hold data as strings of text which can be passed, substituted with a $ prefix, etc. Special interpretation on pure variables allows them to be treated as: • integers • floats • lists • dicts • ...	2012-01-28
3415	User defined sorting and other uses of callbacks in Tcl and Tk When I output a table of results, I usually want it to be sorted in some way. In Tcl, I can use lsort to sort a list - there's an example of it running in a default way [here]. However, there's often a need to order records according to a non-default algorithm, and there are switches such as -integer ...	2011-09-02
3192	Tcl - Some example of HOW TO in handling data files and formats During the Tcl course I was running earlier this week, we got involved in a number of interesting topics such as • How to clean up input lines into lists of fields (use split) • How to reformat awkward fields (use regexp and regsub) • How to combine files that vary in format from year ...	2011-03-04
1282	Stringing together Tcl scripts If you have a series of Tcl scripts that you want to run in a sequence, you can call all of them up in a master script using a series of source commands. This command switches input from the current script (sources) to the new source given as if the text of the sourced file was copied in to the original ...	2011-03-01
2466	Tcl - passing arrays and strings in and back out of procs When you want to pass data INTO a proc in Tcl from a regular variable, you write the variable name with a $ in front of it in the code and the value is substituted. But this doesn't work if (a) you are passing an array (which cannot be expanded into a string or (b) you want to change the value in a ...	2009-10-22
1614	When an array is not an array An array, I was taught, is a sequential series of memory locations in which values of some type are stored. In an array, each of the memory locations is the same size (number of bytes). And so, as I was taught, arrays can be used very efficiently using pointer arithmetic, BUT they need to: a) Be defined ...	2008-04-19
1427	Arrays in Tcl - a demonstration # Array in Tcl   set town(Wycombe) 120000 set town(Marlow) 32567 set town(Amersham) 17000 set town(Melksham) 24000 set town(1) xxxxxx set town(1.) yyyyyyy   # Note that you CAN use numbers as subscripts but you # must be careful because element "1" is different to # element "1." ... or element ...	2007-11-10
1405	Sorting in Tcl - lists and arrays Tcl's lsort command lets you sort a list - and that can be a list of the keys of an array. You can't sort the array, but once you have the list of keys you can sort that and use it to iterate through the array in any order that you like. As everything (except an array) is a string in Tcl, when you ...	2007-10-25
1283	Generating traffic for network testing "Why do you have a random number generator in a scientific language" ask some newcomers to the world of programming ... "shouldn't programming be an exact science?". Well yes, and no. It turns out that a random number generator is exceedingly useful in some instances. Here's a real, live example ...	2007-07-29
779	The fragility of pancakes - and better structures Have you ever hunted around a directory for a file ... you KNOW it's there, but you can't find it - can't see the wood for the trees, if you like, in a listing that spills over many pages? I call such directory structures "pancakes" as they're thin and flat, and they tend not to be very easy to work ...	2006-06-30
122	Passing arrays to procs in Tcl If you're writing a Tcl proc, you'll normally pass in parameters by value, specifying a $ in front of the variable whos contents you want to pass in in the calling sequence: dojob $passin If, however, passin is a Tcl array, tis won't work since $passin cannot be expanded to string. So you'll ...	2006-06-05

ar1	First use of arrays
ar2	Checking if an array key exists
ar3	looping though an array with array get
ar_rail	Setting up an array and sorting the elements by key
arr_log	Access log counter using arrays
arr_log_2	Selecting elements from an array - glob matching to keys
arr_log_3	Passing arrays in and out of procs - using upvar
dla	list, array, dict
ifinder	search for icon references; list icon names
ifinder2	search for icon references and count them
stfinal	final exercise - array of dialling codes
topskill	setting up an array of lists, sorting, listing out elements

Arrays in Tcl
A small group learns Tcl on a private course