Amiga Magazin: Amiga-CD 1996 July/AMIGA_1996_7.BIN/ausgabe_7_96/pd-programmierung/perl5_002bin.lha/man/catp/perllol.0

Text File | 1996-03-02 | 24KB | 463 lines

PERLLOL(1)     User Contributed Perl Documentation     PERLLOL(1)


NNNNAAAAMMMMEEEE
       perlLoL - Manipulating Lists of Lists in Perl

DDDDEEEESSSSCCCCRRRRIIIIPPPPTTTTIIIIOOOONNNN
DDDDeeeeccccllllaaaarrrraaaattttiiiioooonnnn aaaannnndddd AAAAcccccccceeeessssssss ooooffff LLLLiiiissssttttssss ooooffff LLLLiiiissssttttssss
       The simplest thing to build is a list of lists (sometimes
       called an array of arrays).  It's reasonably easy to
       understand, and almost everything that applies here will
       also be applicable later on with the fancier data
       structures.

       A list of lists, or an array of an array if you would, is
       just a regular old array @@@@LLLLooooLLLL that you can get at with two
       subscripts, like $$$$LLLLooooLLLL[3][2].  Here's a declaration of the
       array:

           #### aaaassssssssiiiiggggnnnn ttttoooo oooouuuurrrr aaaarrrrrrrraaaayyyy aaaa lllliiiisssstttt ooooffff lllliiiisssstttt rrrreeeeffffeeeerrrreeeennnncccceeeessss
           @@@@LLLLooooLLLL ==== ((((
                  [[[[ """"ffffrrrreeeedddd"""",,,, """"bbbbaaaarrrrnnnneeeeyyyy"""" ]]]],,,,
                  [[[[ """"ggggeeeeoooorrrrggggeeee"""",,,, """"jjjjaaaannnneeee"""",,,, """"eeeellllrrrrooooyyyy"""" ]]]],,,,
                  [[[[ """"hhhhoooommmmeeeerrrr"""",,,, """"mmmmaaaarrrrggggeeee"""",,,, """"bbbbaaaarrrrtttt"""" ]]]],,,,
           ))));;;;

           pppprrrriiiinnnntttt $$$$LLLLooooLLLL[[[[2222]]]][[[[2222]]]];;;;
         bbbbaaaarrrrtttt

       Now you should be very careful that the outer bracket type
       is a round one, that is, parentheses.  That's because
       you're assigning to an @@@@lllliiiisssstttt, so you need parens.  If you
       wanted there _n_o_t to be an @@@@LLLLooooLLLL, but rather just a
       reference to it, you could do something more like this:

           #### aaaassssssssiiiiggggnnnn aaaa rrrreeeeffffeeeerrrreeeennnncccceeee ttttoooo lllliiiisssstttt ooooffff lllliiiisssstttt rrrreeeeffffeeeerrrreeeennnncccceeeessss
           $$$$rrrreeeeffff____ttttoooo____LLLLooooLLLL ==== [[[[
               [[[[ """"ffffrrrreeeedddd"""",,,, """"bbbbaaaarrrrnnnneeeeyyyy"""",,,, """"ppppeeeebbbbbbbblllleeeessss"""",,,, """"bbbbaaaammmmbbbbaaaammmm"""",,,, """"ddddiiiinnnnoooo"""",,,, ]]]],,,,
               [[[[ """"hhhhoooommmmeeeerrrr"""",,,, """"bbbbaaaarrrrtttt"""",,,, """"mmmmaaaarrrrggggeeee"""",,,, """"mmmmaaaaggggggggiiiieeee"""",,,, ]]]],,,,
               [[[[ """"ggggeeeeoooorrrrggggeeee"""",,,, """"jjjjaaaannnneeee"""",,,, """"aaaallllrrrrooooyyyy"""",,,, """"jjjjuuuuddddyyyy"""",,,, ]]]],,,,
           ]]]];;;;

           pppprrrriiiinnnntttt $$$$rrrreeeeffff____ttttoooo____LLLLooooLLLL---->>>>[[[[2222]]]][[[[2222]]]];;;;

       Notice that the outer bracket type has changed, and so our
       access syntax has also changed.  That's because unlike C,
       in perl you can't freely interchange arrays and references
       thereto.  $$$$rrrreeeeffff____ttttoooo____LLLLooooLLLL is a reference to an array, whereas
       @@@@LLLLooooLLLL is an array proper.  Likewise, $$$$LLLLooooLLLL[2] is not an
       array, but an array ref.  So how come you can write these:

           $$$$LLLLooooLLLL[[[[2222]]]][[[[2222]]]]
           $$$$rrrreeeeffff____ttttoooo____LLLLooooLLLL---->>>>[[[[2222]]]][[[[2222]]]]

       instead of having to write these:





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PERLLOL(1)     User Contributed Perl Documentation     PERLLOL(1)


           $$$$LLLLooooLLLL[[[[2222]]]]---->>>>[[[[2222]]]]
           $$$$rrrreeeeffff____ttttoooo____LLLLooooLLLL---->>>>[[[[2222]]]]---->>>>[[[[2222]]]]

       Well, that's because the rule is that on adjacent brackets
       only (whether square or curly), you are free to omit the
       pointer dereferencing array.  But you need not do so for
       the very first one if it's a scalar containing a
       reference, which means that $$$$rrrreeeeffff____ttttoooo____LLLLooooLLLL always needs it.

GGGGrrrroooowwwwiiiinnnngggg YYYYoooouuuurrrr OOOOwwwwnnnn
       That's all well and good for declaration of a fixed data
       structure, but what if you wanted to add new elements on
       the fly, or build it up entirely from scratch?

       First, let's look at reading it in from a file.  This is
       something like adding a row at a time.  We'll assume that
       there's a flat file in which each line is a row and each
       word an element.  If you're trying to develop an @@@@LLLLooooLLLL list
       containing all these, here's the right way to do that:

           wwwwhhhhiiiilllleeee ((((<<<<>>>>)))) {{{{
               @@@@ttttmmmmpppp ==== sssspppplllliiiitttt;;;;
               ppppuuuusssshhhh @@@@LLLLooooLLLL,,,, [[[[ @@@@ttttmmmmpppp ]]]];;;;
           }}}}

       You might also have loaded that from a function:

           ffffoooorrrr $$$$iiii (((( 1111 ........ 11110000 )))) {{{{
               $$$$LLLLooooLLLL[[[[$$$$iiii]]]] ==== [[[[ ssssoooommmmeeeeffffuuuunnnncccc(((($$$$iiii)))) ]]]];;;;
           }}}}

       Or you might have had a temporary variable sitting around
       with the list in it.

           ffffoooorrrr $$$$iiii (((( 1111 ........ 11110000 )))) {{{{
               @@@@ttttmmmmpppp ==== ssssoooommmmeeeeffffuuuunnnncccc(((($$$$iiii))));;;;
               $$$$LLLLooooLLLL[[[[$$$$iiii]]]] ==== [[[[ @@@@ttttmmmmpppp ]]]];;;;
           }}}}

       It's very important that you make sure to use the [[[[]]]] list
       reference constructor.  That's because this will be very
       wrong:

           $$$$LLLLooooLLLL[[[[$$$$iiii]]]] ==== @@@@ttttmmmmpppp;;;;

       You see, assigning a named list like that to a scalar just
       counts the number of elements in @@@@ttttmmmmpppp, which probably
       isn't what you want.

       If you are running under uuuusssseeee ssssttttrrrriiiicccctttt, you'll have to add
       some declarations to make it happy:






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           uuuusssseeee ssssttttrrrriiiicccctttt;;;;
           mmmmyyyy((((@@@@LLLLooooLLLL,,,, @@@@ttttmmmmpppp))));;;;
           wwwwhhhhiiiilllleeee ((((<<<<>>>>)))) {{{{
               @@@@ttttmmmmpppp ==== sssspppplllliiiitttt;;;;
               ppppuuuusssshhhh @@@@LLLLooooLLLL,,,, [[[[ @@@@ttttmmmmpppp ]]]];;;;
           }}}}

       Of course, you don't need the temporary array to have a
       name at all:

           wwwwhhhhiiiilllleeee ((((<<<<>>>>)))) {{{{
               ppppuuuusssshhhh @@@@LLLLooooLLLL,,,, [[[[ sssspppplllliiiitttt ]]]];;;;
           }}}}

       You also don't have to use _p_u_s_h_(_).  You could just make a
       direct assignment if you knew where you wanted to put it:

           mmmmyyyy ((((@@@@LLLLooooLLLL,,,, $$$$iiii,,,, $$$$lllliiiinnnneeee))));;;;
           ffffoooorrrr $$$$iiii (((( 0000 ........ 11110000 ))))
               $$$$lllliiiinnnneeee ==== <<<<>>>>;;;;
               $$$$LLLLooooLLLL[[[[$$$$iiii]]]] ==== [[[[ sssspppplllliiiitttt '''' '''',,,, $$$$lllliiiinnnneeee ]]]];;;;
           }}}}

       or even just

           mmmmyyyy ((((@@@@LLLLooooLLLL,,,, $$$$iiii))));;;;
           ffffoooorrrr $$$$iiii (((( 0000 ........ 11110000 ))))
               $$$$LLLLooooLLLL[[[[$$$$iiii]]]] ==== [[[[ sssspppplllliiiitttt '''' '''',,,, <<<<>>>> ]]]];;;;
           }}}}

       You should in general be leary of using potential list
       functions in a scalar context without explicitly stating
       such.  This would be clearer to the casual reader:

           mmmmyyyy ((((@@@@LLLLooooLLLL,,,, $$$$iiii))));;;;
           ffffoooorrrr $$$$iiii (((( 0000 ........ 11110000 ))))
               $$$$LLLLooooLLLL[[[[$$$$iiii]]]] ==== [[[[ sssspppplllliiiitttt '''' '''',,,, ssssccccaaaallllaaaarrrr((((<<<<>>>>)))) ]]]];;;;
           }}}}

       If you wanted to have a $$$$rrrreeeeffff____ttttoooo____LLLLooooLLLL variable as a
       reference to an array, you'd have to do something like
       this:

           wwwwhhhhiiiilllleeee ((((<<<<>>>>)))) {{{{
               ppppuuuusssshhhh @@@@$$$$rrrreeeeffff____ttttoooo____LLLLooooLLLL,,,, [[[[ sssspppplllliiiitttt ]]]];;;;
           }}}}

       Actually, if you were using strict, you'd not only have to
       declare $$$$rrrreeeeffff____ttttoooo____LLLLooooLLLL as you had to declare @@@@LLLLooooLLLL, but you'd
       _a_l_s_o having to initialize it to a reference to an empty
       list.  (This was a bug in 5.001m that's been fixed for the
       5.002 release.)





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PERLLOL(1)     User Contributed Perl Documentation     PERLLOL(1)


           mmmmyyyy $$$$rrrreeeeffff____ttttoooo____LLLLooooLLLL ==== [[[[]]]];;;;
           wwwwhhhhiiiilllleeee ((((<<<<>>>>)))) {{{{
               ppppuuuusssshhhh @@@@$$$$rrrreeeeffff____ttttoooo____LLLLooooLLLL,,,, [[[[ sssspppplllliiiitttt ]]]];;;;
           }}}}

       Ok, now you can add new rows.  What about adding new
       columns?  If you're just dealing with matrices, it's often
       easiest to use simple assignment:

           ffffoooorrrr $$$$xxxx ((((1111 ........ 11110000)))) {{{{
               ffffoooorrrr $$$$yyyy ((((1111 ........ 11110000)))) {{{{
                   $$$$LLLLooooLLLL[[[[$$$$xxxx]]]][[[[$$$$yyyy]]]] ==== ffffuuuunnnncccc(((($$$$xxxx,,,, $$$$yyyy))));;;;
               }}}}
           }}}}

           ffffoooorrrr $$$$xxxx (((( 3333,,,, 7777,,,, 9999 )))) {{{{
               $$$$LLLLooooLLLL[[[[$$$$xxxx]]]][[[[22220000]]]] ++++==== ffffuuuunnnncccc2222(((($$$$xxxx))));;;;
           }}}}

       It doesn't matter whether those elements are already there
       or not: it'll gladly create them for you, setting
       intervening elements to uuuunnnnddddeeeeffff as need be.

       If you just wanted to append to a row, you'd have to do
       something a bit funnier looking:

           #### aaaadddddddd nnnneeeewwww ccccoooolllluuuummmmnnnnssss ttttoooo aaaannnn eeeexxxxiiiissssttttiiiinnnngggg rrrroooowwww
           ppppuuuusssshhhh @@@@{{{{ $$$$LLLLooooLLLL[[[[0000]]]] }}}},,,, """"wwwwiiiillllmmmmaaaa"""",,,, """"bbbbeeeettttttttyyyy"""";;;;

       Notice that I _c_o_u_l_d_n_'_t just say:

           ppppuuuusssshhhh $$$$LLLLooooLLLL[[[[0000]]]],,,, """"wwwwiiiillllmmmmaaaa"""",,,, """"bbbbeeeettttttttyyyy"""";;;;  #### WWWWRRRROOOONNNNGGGG!!!!

       In fact, that wouldn't even compile.  How come?  Because
       the argument to _p_u_s_h_(_) must be a real array, not just a
       reference to such.

AAAAcccccccceeeessssssss aaaannnndddd PPPPrrrriiiinnnnttttiiiinnnngggg
       Now it's time to print your data structure out.  How are
       you going to do that?  Well, if you only want one of the
       elements, it's trivial:

           pppprrrriiiinnnntttt $$$$LLLLooooLLLL[[[[0000]]]][[[[0000]]]];;;;

       If you want to print the whole thing, though, you can't
       just say

           pppprrrriiiinnnntttt @@@@LLLLooooLLLL;;;;         #### WWWWRRRROOOONNNNGGGG

       because you'll just get references listed, and perl will
       never automatically dereference things for you.  Instead,
       you have to roll yourself a loop or two.  This prints the
       whole structure, using the shell-style _f_o_r_(_) construct to
       loop across the outer set of subscripts.



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PERLLOL(1)     User Contributed Perl Documentation     PERLLOL(1)


           ffffoooorrrr $$$$aaaarrrreeeeffff (((( @@@@LLLLooooLLLL )))) {{{{
               pppprrrriiiinnnntttt """"\\\\tttt [[[[ @@@@$$$$aaaarrrreeeeffff ]]]],,,,\\\\nnnn"""";;;;
           }}}}

       If you wanted to keep track of subscripts, you might do
       this:

           ffffoooorrrr $$$$iiii (((( 0000 ........ $$$$####LLLLooooLLLL )))) {{{{
               pppprrrriiiinnnntttt """"\\\\tttt eeeelllltttt $$$$iiii iiiissss [[[[ @@@@{{{{$$$$LLLLooooLLLL[[[[$$$$iiii]]]]}}}} ]]]],,,,\\\\nnnn"""";;;;
           }}}}

       or maybe even this.  Notice the inner loop.

           ffffoooorrrr $$$$iiii (((( 0000 ........ $$$$####LLLLooooLLLL )))) {{{{
               ffffoooorrrr $$$$jjjj (((( 0000 ........ $$$$####{{{{$$$$LLLLooooLLLL[[[[$$$$iiii]]]]}}}} )))) {{{{
                   pppprrrriiiinnnntttt """"eeeelllltttt $$$$iiii $$$$jjjj iiiissss $$$$LLLLooooLLLL[[[[$$$$iiii]]]][[[[$$$$jjjj]]]]\\\\nnnn"""";;;;
               }}}}
           }}}}

       As you can see, it's getting a bit complicated.  That's
       why sometimes is easier to take a temporary on your way
       through:

           ffffoooorrrr $$$$iiii (((( 0000 ........ $$$$####LLLLooooLLLL )))) {{{{
               $$$$aaaarrrreeeeffff ==== $$$$LLLLooooLLLL[[[[$$$$iiii]]]];;;;
               ffffoooorrrr $$$$jjjj (((( 0000 ........ $$$$####{{{{$$$$aaaarrrreeeeffff}}}} )))) {{{{
                   pppprrrriiiinnnntttt """"eeeelllltttt $$$$iiii $$$$jjjj iiiissss $$$$LLLLooooLLLL[[[[$$$$iiii]]]][[[[$$$$jjjj]]]]\\\\nnnn"""";;;;
               }}}}
           }}}}

       Hm... that's still a bit ugly.  How about this:

           ffffoooorrrr $$$$iiii (((( 0000 ........ $$$$####LLLLooooLLLL )))) {{{{
               $$$$aaaarrrreeeeffff ==== $$$$LLLLooooLLLL[[[[$$$$iiii]]]];;;;
               $$$$nnnn ==== @@@@$$$$aaaarrrreeeeffff ---- 1111;;;;
               ffffoooorrrr $$$$jjjj (((( 0000 ........ $$$$nnnn )))) {{{{
                   pppprrrriiiinnnntttt """"eeeelllltttt $$$$iiii $$$$jjjj iiiissss $$$$LLLLooooLLLL[[[[$$$$iiii]]]][[[[$$$$jjjj]]]]\\\\nnnn"""";;;;
               }}}}
           }}}}


SSSSlllliiiicccceeeessss
       If you want to get at a slide (part of a row) in a
       multidimensional array, you're going to have to do some
       fancy subscripting.  That's because while we have a nice
       synonym for single elements via the pointer arrow for
       dereferencing, no such convenience exists for slices.
       (Remember, of course, that you can always write a loop to
       do a slice operation.)

       Here's how to do one operation using a loop.  We'll assume
       an @@@@LLLLooooLLLL variable as before.





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PERLLOL(1)     User Contributed Perl Documentation     PERLLOL(1)


           @@@@ppppaaaarrrrtttt ==== (((())));;;;
           $$$$xxxx ==== 4444;;;;
           ffffoooorrrr (((($$$$yyyy ==== 7777;;;; $$$$yyyy <<<< 11113333;;;; $$$$yyyy++++++++)))) {{{{
               ppppuuuusssshhhh @@@@ppppaaaarrrrtttt,,,, $$$$LLLLooooLLLL[[[[$$$$xxxx]]]][[[[$$$$yyyy]]]];;;;
           }}}}

       That same loop could be replaced with a slice operation:

           @@@@ppppaaaarrrrtttt ==== @@@@{{{{ $$$$LLLLooooLLLL[[[[4444]]]] }}}} [[[[ 7777........11112222 ]]]];;;;

       but as you might well imagine, this is pretty rough on the
       reader.

       Ah, but what if you wanted a _t_w_o_-_d_i_m_e_n_s_i_o_n_a_l _s_l_i_c_e, such
       as having $$$$xxxx run from 4..8 and $$$$yyyy run from 7 to 12?  Hm...
       here's the simple way:

           @@@@nnnneeeewwwwLLLLooooLLLL ==== (((())));;;;
           ffffoooorrrr (((($$$$ssssttttaaaarrrrttttxxxx ==== $$$$xxxx ==== 4444;;;; $$$$xxxx <<<<==== 8888;;;; $$$$xxxx++++++++)))) {{{{
               ffffoooorrrr (((($$$$ssssttttaaaarrrrttttyyyy ==== $$$$yyyy ==== 7777;;;; $$$$xxxx <<<<==== 11112222;;;; $$$$yyyy++++++++)))) {{{{
                   $$$$nnnneeeewwwwLLLLooooLLLL[[[[$$$$xxxx ---- $$$$ssssttttaaaarrrrttttxxxx]]]][[[[$$$$yyyy ---- $$$$ssssttttaaaarrrrttttyyyy]]]] ==== $$$$LLLLooooLLLL[[[[$$$$xxxx]]]][[[[$$$$yyyy]]]];;;;
               }}}}
           }}}}

       We can reduce some of the looping through slices

           ffffoooorrrr (((($$$$xxxx ==== 4444;;;; $$$$xxxx <<<<==== 8888;;;; $$$$xxxx++++++++)))) {{{{
               ppppuuuusssshhhh @@@@nnnneeeewwwwLLLLooooLLLL,,,, [[[[ @@@@{{{{ $$$$LLLLooooLLLL[[[[$$$$xxxx]]]] }}}} [[[[ 7777........11112222 ]]]] ]]]];;;;
           }}}}

       If you were into Schwartzian Transforms, you would
       probably have selected map for that

           @@@@nnnneeeewwwwLLLLooooLLLL ==== mmmmaaaapppp {{{{ [[[[ @@@@{{{{ $$$$LLLLooooLLLL[[[[$$$$____]]]] }}}} [[[[ 7777........11112222 ]]]] ]]]] }}}} 4444 ........ 8888;;;;

       Although if your manager accused of seeking job security
       (or rapid insecurity) through inscrutable code, it would
       be hard to argue. :-) If I were you, I'd put that in a
       function:

           @@@@nnnneeeewwwwLLLLooooLLLL ==== sssspppplllliiiicccceeee____2222DDDD(((( \\\\@@@@LLLLooooLLLL,,,, 4444 ====>>>> 8888,,,, 7777 ====>>>> 11112222 ))));;;;
           ssssuuuubbbb sssspppplllliiiicccceeee____2222DDDD {{{{
               mmmmyyyy $$$$llllrrrrrrrr ==== sssshhhhiiiifffftttt;;;;        #### rrrreeeeffff ttttoooo lllliiiisssstttt ooooffff lllliiiisssstttt rrrreeeeffffssss!!!!
               mmmmyyyy (((($$$$xxxx____lllloooo,,,, $$$$xxxx____hhhhiiii,,,,
                   $$$$yyyy____lllloooo,,,, $$$$yyyy____hhhhiiii)))) ==== @@@@____;;;;

               rrrreeeettttuuuurrrrnnnn mmmmaaaapppp {{{{
                   [[[[ @@@@{{{{ $$$$llllrrrrrrrr---->>>>[[[[$$$$____]]]] }}}} [[[[ $$$$yyyy____lllloooo ........ $$$$yyyy____hhhhiiii ]]]] ]]]]
               }}}} $$$$xxxx____lllloooo ........ $$$$xxxx____hhhhiiii;;;;
           }}}}


SSSSEEEEEEEE AAAALLLLSSSSOOOO
       _p_e_r_l_d_a_t_a(1), _p_e_r_l_r_e_f(1), _p_e_r_l_d_s_c(1)



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PERLLOL(1)     User Contributed Perl Documentation     PERLLOL(1)


AAAAUUUUTTTTHHHHOOOORRRR
       Tom Christiansen <[e-mail]>

       Last udpate: Sat Oct  7 19:35:26 MDT 1995





















































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