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

Tcl                                                                                                   lmap(3tcl)