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lmap(n)			     Tcl Built-In Commands		       lmap(n)

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NAME
       lmap  -	Iterate	over all elements in one or more lists and collect re-
       sults

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 nor-
       mally 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	 accu-
       mulator 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(n),  continue(n),	for(n),	 foreach(n),  while(n),	 list(n), lap-
       pend(n),	 lassign(n),  lindex(n),  linsert(n),	llength(n),   lpop(n),
       lrange(n),    lremove(n),    lrepeat(n),	   lreplace(n),	  lreverse(n),
       lsearch(n), lset(n), lsort(n)

KEYWORDS
       foreach,	iteration, list, loop, map

Tcl								       lmap(n)

NAME | SYNOPSIS | DESCRIPTION | EXAMPLES | SEE ALSO | KEYWORDS

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