Question

I am trying to populate an array dynamically rather than setting it manually by running a counter like below:

set all_list  { <my list>}
set num_pc_a_b 10

for {set i 0 ;set j 0 ; set k 0} {$j < $num_pc_a_b} {incr j; incr i ;incr k} {
    array set link_map  {[lindex $all_list $i] $j $k 0 }
}

and hoping to access the variables like below:

foreach {key value value1 value2} [array get link_map] {
    puts "key is $key"
    puts "value is $value"
    puts "value is $value1"
    puts "value is $value2"
}

But it doesn’t work . Am I doing something wrong here ?

Answer 1

It’s not immediately obvious to me what you really wanted to do, so I’ll make some guesses.

In either case note that your usage of array set ... appears to be wrong: this command takes the name of an array and a list which it interprets as alternating keys and values, creating an entry in that array for each key mapped to the value following that key. You seem to want to just set a specific key to a specific value on each iteration — this is done by set array(key) value syntax.

Also note that in your example the j, i and k variables seem to have the same values on each iteration. Supposedly it’s just a left-over from a real-world code, but otherwise just one variable would be enough.

Guess one: you want to map each key to a list of values. This won’t work like in your example as in Tcl an array maps each key to one value; this value might be a list though. If my guess is correct, the way to go is:

for {set i 0 ;set j 0 ; set k 0} {$j < $num_pc_a_b} {incr j; incr i ;incr k} {
    set link_map([lindex $all_list $i]) [list $j $k 0]
}
foreach {key val} [array get link_map] {
    foreach {v1 v2 v3} $val break ;# see a note below
    puts "key is $key"
    puts "value is $v1"
    puts "value is $v2"
    puts "value is $v3"
}

Guess two: judging from your usage of foreach for displaying, you might want to not use an array at all, but rather a list:

set links [list]
for {set i 0 ;set j 0 ; set k 0} {$j < $num_pc_a_b} {incr j; incr i ;incr k} {
    lappend links [lindex $all_list $i] $j $k 0
}
foreach {key v1 v2 v3} $links {
    puts "key is $key"
    puts "value is $v1"
    puts "value is $v2"
    puts "value is $v3"
}

You could as well make not a flat list but a list of alterating keys and values, with each value being a [list $j $k 0] as in the first guess example.

Update

Guess three. You tagged our question as multidimensional-array. I do not see any trace of multi-dimentionality in your snippets, but if you really wanted it, the usual paradigm in Tcl for this is to use compound keys. For instance, if you want to key your array by values of j, i and k these variables have on each iteration, use something like:

for {set i 0 ;set j 0 ; set k 0} {$j < $num_pc_a_b} {incr j; incr i ;incr k} {
    set link_map($i,$j,$k) ...
}

This creates a string concatenating three values using a comma and uses the result as the key.

---

The usage of foreach ... break to explode a list is a neat trick, but if you have Tcl 8.5 or later, use lassign $list v1 v2 v3 instead.