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lmap(3tcl) Tcl Built-In Commands lmap(3tcl) 





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







  

    
    Tcl