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
________________________________________________________________________________________________________________

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