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# Syntax Question

Posted on 2004-12-01
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What is the meaning of the line below:

my \$hh=join('+',sort {\$a <=> \$b} @l) ; \$f[\$t]=\$hh ;

Also could you explain :

foreach my \$m (split(/\+/,\$f[\$t])) {
push @cl,\$mbd[\$m] ;
}
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Question by:Cosine_Consultants

LVL 18

Expert Comment

ID: 12717346
have you considered reading the documentation that comes with Perl?
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LVL 13

Expert Comment

ID: 12717488
What algorithm was the file encrypted with?

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LVL 13

Expert Comment

ID: 12717503
Argh, damn quickpost. :)

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LVL 6

Accepted Solution

sstouk earned 2000 total points
ID: 12717976
This portion:

my \$hh=join('+',sort {\$a <=> \$b} @l) ;  \$f[\$t]=\$hh ;

Array @l contains elements that are sorted from lowest to highest value and joined with the '+' sign
The result is a scalar, assigned to variable \$hh, which is in turn assigned to the element \$t or the array @f;

For example,
let's say
@l = ('222','333','111');
After:
\$hh=join('+',sort {\$a <=> \$b} @l) ;

\$hh will be equal to  '1+2+3'
and if We have an array with elements
@f = ('first','second','third');
and \$t = 1, then after
\$f[\$t]=\$hh ;

\$f[\$t] will be '1+2+3';
And
@f will be equal to ('first','1+2+3','third');

##########################################################
The Next process takes the value
'1+2+3' and splits it in places where the character '+' is into elements.
It loops though the elements, assigning each current value to variable \$m

foreach my \$m (split(/\+/,\$f[\$t]))
{
push @cl,\$mbd[\$m] ;
}

For each iteration, variable \$m will take a value of  '1', then '2', then '3' because we split the Scalar into these elements.

There is an array @mbd with some elements in it;
If For Example
@mbd = ('First','Second','Third','Fourth');

Then element \$mbd[1] is "Second";
Element \$mbd[2] is "Thurd"; etc.

So when we loop though the splitted elements of the scalar variable \$f[\$t] (which is just one element of an array @f) we get
\$mbd[1] then \$mbd[2]  then \$mbd[3]  because \$m = 1, then \$m = 2, then \$m = 3
Command 'push'; pushes the values of the array \$mbd into a new array - @cl

After the loop finishes, @cl = ('Second','Third','Fourth');

###################################################################

There is nothing more to it.

0

LVL 6

Expert Comment

ID: 12718109
Change
#################
For example,
let's say
@l = ('222','333','111');
#################
To:
#################
For example,
let's say
@l = ('2','3','1');
#################
0

LVL 5

Expert Comment

ID: 12718138
a. as some has pointed, you're gonna have to buy a good Perl book (I recommend on "Learning Perl" if you're new to programming and or perl. Also, "Programming Perl". Both of them are 3rd edtioins from O'reilly.

b. Here is a sample code for your first question:
my @l = (4,2,8,4,10);
my \$hh=join('+',sort {\$a <=> \$b} @l) ;
print "\$hh\n";

sort {\$a <=> \$b} @l

sort function gets as parameters
a. sorting function (which defaults to asciibetically)
b. a list to sort
Here the sorting function is to sort numerically. This is the meaning of the "Spaceship" operator (<=>). \$a and \$b are special variables to sort, which tells it, in that case to sort in ascending order.

join gets as parameters
a. a joiner character
b. a list to join.
It returns as result the string.

Run this code to see what I mean.

\$f[\$t]=\$hh ;

This is a simple assignment of the result to the \$t element in @f array.

c.
foreach my \$m (split(/\+/,\$f[\$t])) {
push @cl,\$mbd[\$m] ;
}

split(/\+/,\$f[\$t])

split is the reverse of join.
It gets
a. the character to split according to
b. the string to split
It returns a list.

This loop iterates on each element of this list, (which seems like a list of array's indices) in each iteration pushing the result to @cl array.
0

LVL 85

Expert Comment

ID: 12723840
c. could also be
push @cl,@mbd[split(/\+/,\$f[\$t]];
or, combining the two:
push @cl,@mbd[sort {\$a <=> \$b} @l];

see
perldoc -f sort
perldoc -f join
perldoc -f split
perldoc -f push
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