Reading data into muti-dimentional array - in perl

Shell Programming and Scripting
1

Just want to learn how these are read into array but I don't seem to get it right what do I go wrong?
Below is the sample

Thanks

input

1 2 3 4
5 6 7 8
9 1 2 3
4 5 6 7

#!/usr/bin/perl

open (InFILE,"input");

while (<InFILE>) {

@ar = split ;

$arref = \@ar;

push(@multiarray,$arref);

}

for ($i=0;$i<=4;$i++){
for ($j=0;$j<=4;$j++){

print " $multiarray[$i][$j] ";
}

2

I don't really know why you put your program like this as it seems really awkward, but this seems like this may do you want:

Output:

1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7

Hint: the "my" is crucial here --- you have made your program unnecessarily complex that you have actually set for yourself a subtle trap without your realizing it that is tedious to locate. Why "my" is needed here is left for your exploration to encourage you to find out the answer yourself.

3

cbkihong,

Thanks it did work. I am very new to perl and I am trying to understand how multi-dimentiona array is read in.
Interesting about "my" I will investigate further!
Zap

4

what you might want to take a look at is:

Learning Perl Objects, References & Modules.
5.2. Viewing Complex Data with Data :: Dumper

I used data dumper on your script above and this is what i get.

$VAR1 = [
          '1',
          '2',
          '3',
          '4'
        ];
$VAR1 = [
          '5',
          '6',
          '7',
          '8'
        ];
$VAR1 = [
          '9',
          '1',
          '2',
          '3'
        ];
$VAR1 = [
          '4',
          '5',
          '6',
          '7'
        ];

i think i know what your asking and if that is the case this is what is happening.

LINE: 1 )while (<InFILE> ) {
LINE: 2 )
LINE: 3 )@ar = split ;
LINE: 4 )
LINE: 5 )$arref = \@ar;
LINE: 6 )
LINE: 7 )push(@multiarray,$arref);
.....
....

line 1 says read each line in the file.
line 3 says for each space add a new element to @ar for each items read in $_. (IE: for the first line read in @ar=qw(1 2 3 4):wink:
line 7 says for each entry to @ar create an anonymous array inside @multiarray. (IE:
@mulriarray=(
[1,2,3,4];
);
)

if you are trying to do something else be as detailed in your question as possable and i am sure we can get you sorted out and pointing in the right direction.

5

I decided to unveil the trap.

Without the "my", the result I got (with the original script) was

4 5 6 7 4 5 6 7 4 5 6 7 4 5 6 7

(4 5 6 7 printed four times). Shouldn't get the first three lines printed at all because all four references saved into @multiarray point to the same symbol table entry, which always refers to the most recent anonymous list read (each assignment to @ar overwrites the previous entry). That explains why four consecutive 4 5 6 7 is resulted. The line read from file is correct but the output doesn't.

With @ar declared "my", it becomes a lexical array variable which gets expired on each loop iteration (so at the time the block ends its reference count drops to 1 -- the only reference left is the one saved in @multiarray). Assignment to @ar in the next iteration no longer affects the previous saved reference because it is now a different variable from the earlier @ar.

That's why I said the trap is a subtle one that is not obvious from the surface. :wink:

6

Thanks for the response and expalination.

I kind of understand the scoping of the array using "my" and yes it seems incredably tricky with referencing.

I never have thought that it would use the same addresses eventhough the content changed.

I'll play around abit more to gain more understanding of it!