NAME

       lmap - Iterate over all elements in one or more lists and collect results

SYNOPSIS

       lmap varname list body
       lmap varlist1 list1 ?varlist2 list2 ...? body
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DESCRIPTION

       The  lmap  command implements a loop where the loop variable(s) take on values from one or
       more lists, and the loop returns a list of results collected from each iteration.

       In the simplest case there is one loop variable, varname, and one list, list,  that  is  a
       list  of  values to assign to varname. The body argument is a Tcl script. For each element
       of list (in order from first to last), lmap assigns the contents of the element to varname
       as  if  the  lindex  command  had  been  used  to  extract the element, then calls the Tcl
       interpreter to execute body. If execution of the body completes normally then  the  result
       of the body is appended to an accumulator list. lmap returns the accumulator list.

       In  the  general  case  there can be more than one value list (e.g., list1 and list2), and
       each value list can be associated with a  list  of  loop  variables  (e.g.,  varlist1  and
       varlist2).  During  each  iteration of the loop the variables of each varlist are assigned
       consecutive values from the corresponding list. Values in each list are used in order from
       first to last, and each value is used exactly once. The total number of loop iterations is
       large enough to use up all the values from all the value lists. If a value list  does  not
       contain enough elements for each of its loop variables in each iteration, empty values are
       used for the missing elements.

       The break and continue statements may be invoked inside body, with the same effect  as  in
       the  for  and foreach commands. In these cases the body does not complete normally and the
       result is not appended to the accumulator list.

EXAMPLES

       Zip lists together:

              set list1 {a b c d}
              set list2 {1 2 3 4}
              set zipped [lmap a $list1 b $list2 {list $a $b}]
              # The value of zipped is "{a 1} {b 2} {c 3} {d 4}"

       Filter a list to remove odd values:

              set values {1 2 3 4 5 6 7 8}
              proc isEven {n} {expr {($n % 2) == 0}}
              set goodOnes [lmap x $values {expr {
                  [isEven $x] ? $x : [continue]
              }}]
              # The value of goodOnes is "2 4 6 8"

       Take a prefix from a list based on the contents of the list:

              set values {8 7 6 5 4 3 2 1}
              proc isGood {counter} {expr {$n > 3}}
              set prefix [lmap x $values {expr {
                  [isGood $x] ? $x : [break]
              }}]
              # The value of prefix is "8 7 6 5 4"

SEE ALSO

       break(3tcl), continue(3tcl), for(3tcl), foreach(3tcl), while(3tcl)

KEYWORDS

       foreach, iteration, list, loop, map