Return index of duplicates in list of list in tcl 8.4

Question

I have this kind of list : { A D C } { D S D } { A S D } { Y D D }

I want to list all the index that have duplicates in the same index of the sublist. For example if I want to serach every "D" at index 2 in sublist, I want to know the index of the list (here 0 and 3)

here is the code :

proc findElement {lst idx value} {
    set i 0
    foreach sublist $lst {
        if {[string equal [lindex $sublist $idx] $value]} {
            return $i
        }
        incr i
    }
    return -1
}

When i call it findElement $toto 1 D

it returns only 0 !

Why ?

Answer 1

Because you have a return statement when it finds a match when $i = 0.

Try the following which instead returns a list of all the matching indexes

proc findElement {lst idx value} {
    set i 0
    set return_list [list]
    foreach sublist $lst {
       puts "i=$i sublist=$sublist"
        if {[string equal [lindex $sublist $idx] $value]} {
            puts "Found $i"
            lappend return_list $i
        }
        incr i
    }
    return $return_list
}

Answer 2

You can do a shorter and faster version with lsearch -all -exact -index.

proc findElement {lst idx value} {
   return [lsearch -all -exact -index $idx $lst $value]
}