move array elements to hash

Hi,
I am trying to move array elements (populated from the ) into a
hash
as pairs [i] and [i + 1] and then print them out using the code below.
If I enter "bob" as the first element and hit enter I get the
error messages below. I guess there are multiple problems with my
code.
For one it appears that my $kv variable is supposed to take numeric
values. I'm not sure if this is the reason the program aborts once
I hit enter after my first entry (i.e. "bob").
Any hints on why I my $kv varible is expected to be numeric
or any other obvious problems with my code?

Thanks,
M


Useless use of array element in void context at L2_Q9.pl line 23.
input key/value pairs: first a key then return, then a value then
return, etc. To stop entering key/value pairs type 'stop'
jim
Argument "stop" isn't numeric in numeric eq (==) at L2_Q9.pl line 17,
line 1.
Argument "jim" isn't numeric in numeric eq (==) at L2_Q9.pl line 17,
line 1.
Odd number of elements in hash assignment at L2_Q9.pl line 23,
line 1.
Use of uninitialized value in concatenation (.) or string at L2_Q9.pl
line 28, line 1.
jim +>


#!/usr/bin/perl -w
use strict;

my %hash;
my $kv;
my @kv;
my @v;
my $i;
my $key;
my $value;

#create key - value pairs to go into a hash by first entering each
into a list @k or @v
print "input key/value pairs: first a key then return, then a value
then return, etc. To stop entering key/value pairs type 'stop'\n";
while ($kv = ) {
chomp($kv);
push(@kv, $kv);
last if ($kv == "stop");
}

# move each key or value located at each index of array @kv into a
hash so that they pair up e.g. $kv[i] with $kv[i +1] etc.

for($i = 0; $i < $#kv + 1; $i++) {
%hash = $kv[$i] => $kv[$i + 1];
$i++;
}

while ( ($key, $value) = each %hash ) {
print "$key +> $value\n";
}


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Re: move array elements to hash

On 11-04-14 03:29 PM, mark baumeister wrote:
> #create key - value pairs to go into a hash by first entering each
> into a list @k or @v
> print "input key/value pairs: first a key then return, then a value
> then return, etc. To stop entering key/value pairs type 'stop'\n";
> while ($kv =) {
> chomp($kv);
> push(@kv, $kv);
> last if ($kv == "stop");
> }
>

Have you tried:

%hash = @kv;


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Re: move array elements to hash

On 14/04/2011 20:29, mark baumeister wrote:
> Hi,
> I am trying to move array elements (populated from the) into a
> hash
> as pairs [i] and [i + 1] and then print them out using the code below.
> If I enter "bob" as the first element and hit enter I get the
> error messages below. I guess there are multiple problems with my
> code.
> For one it appears that my $kv variable is supposed to take numeric
> values. I'm not sure if this is the reason the program aborts once
> I hit enter after my first entry (i.e. "bob").
> Any hints on why I my $kv varible is expected to be numeric
> or any other obvious problems with my code?
>
> Thanks,
> M
>
>
> Useless use of array element in void context at L2_Q9.pl line 23.
> input key/value pairs: first a key then return, then a value then
> return, etc. To stop entering key/value pairs type 'stop'
> jim
> Argument "stop" isn't numeric in numeric eq (==) at L2_Q9.pl line 17,
> line 1.
> Argument "jim" isn't numeric in numeric eq (==) at L2_Q9.pl line 17,
> line 1.
> Odd number of elements in hash assignment at L2_Q9.pl line 23,
> line 1.
> Use of uninitialized value in concatenation (.) or string at L2_Q9.pl
> line 28, line 1.
> jim +>
>
>
> #!/usr/bin/perl -w
> use strict;
>
> my %hash;
> my $kv;
> my @kv;
> my @v;
> my $i;
> my $key;
> my $value;
>
> #create key - value pairs to go into a hash by first entering each
> into a list @k or @v
> print "input key/value pairs: first a key then return, then a value
> then return, etc. To stop entering key/value pairs type 'stop'\n";
> while ($kv =) {
> chomp($kv);
> push(@kv, $kv);
> last if ($kv == "stop");

The reason you are getting these errors is because you are using a
numeric comparison. Write

last if $kv eq "stop";

for a string comparison.

> }
>
> # move each key or value located at each index of array @kv into a
> hash so that they pair up e.g. $kv[i] with $kv[i +1] etc.
>
> for($i = 0; $i< $#kv + 1; $i++) {
> %hash = $kv[$i] => $kv[$i + 1];
> $i++;
> }
>
> while ( ($key, $value) = each %hash ) {
> print "$key +> $value\n";
> }

Your loop should read

for ($i = 0; $i < @kv; $i += 2) {
$hash{$kv[$i]} = $kv[$i + 1];
}

but, as Shawn says, it is a dreadful way to populate a Perl hash.

%hash = @kv;

works fine as long as the data in the array are ordered as you
describe, and there is an even number of elements.

Rob

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Re: move array elements to hash

mark baumeister wrote:
> Hi,

Hello,

> I am trying to move array elements (populated from the) into a
> hash
> as pairs [i] and [i + 1] and then print them out using the code below.
> If I enter "bob" as the first element and hit enter I get the
> error messages below. I guess there are multiple problems with my
> code.
> For one it appears that my $kv variable is supposed to take numeric
> values. I'm not sure if this is the reason the program aborts once
> I hit enter after my first entry (i.e. "bob").
> Any hints on why I my $kv varible is expected to be numeric
> or any other obvious problems with my code?
>
>
> Useless use of array element in void context at L2_Q9.pl line 23.

That is from the line:

> %hash = $kv[$i] => $kv[$i + 1];

You get that because the '=' operator has higher precedence than the
'=>' operator and perl sees it as:

( %hash = $kv[$i] ) => $kv[$i + 1];

And the array element $kv[$i + 1] is just sitting there in void context.

You need to use parentheses around a list on the right-hand side of the
'=' operator:

%hash = ( $kv[ $i ], $kv[ $i + 1 ] );


> input key/value pairs: first a key then return, then a value then
> return, etc. To stop entering key/value pairs type 'stop'
> jim
> Argument "stop" isn't numeric in numeric eq (==) at L2_Q9.pl line 17,
> line 1.
> Argument "jim" isn't numeric in numeric eq (==) at L2_Q9.pl line 17,
> line 1.

You get those to from this line:

> last if ($kv == "stop");

Where $ky contains "jim". You are trying to compare two non-numeric
values with a numeric comparison operator so perl warns you that they
are non-numeric. The result of this is that perl will convert "jim" and
"stop" to the number 0 before comparing.

You have to use the string comparison operators to compare two strings.


> Odd number of elements in hash assignment at L2_Q9.pl line 23,
> line 1.

That is also from the line:

> %hash = $kv[$i] => $kv[$i + 1];

Where you are only assigning $kv[$i] to %hash and 1 is an odd number.


> Use of uninitialized value in concatenation (.) or string at L2_Q9.pl
> line 28, line 1.

That is from the line:

> print "$key +> $value\n";

Because %hash has been assigned an odd number of elements that means
that one $value is uninitialized which gives this warning.


> #!/usr/bin/perl -w
> use strict;
>
> my %hash;
> my $kv;
> my @kv;
> my @v;
> my $i;
> my $key;
> my $value;
>
> #create key - value pairs to go into a hash by first entering each
> into a list @k or @v
> print "input key/value pairs: first a key then return, then a value
> then return, etc. To stop entering key/value pairs type 'stop'\n";
> while ($kv =) {
> chomp($kv);
> push(@kv, $kv);
> last if ($kv == "stop");
> }
>
> # move each key or value located at each index of array @kv into a
> hash so that they pair up e.g. $kv[i] with $kv[i +1] etc.
>
> for($i = 0; $i< $#kv + 1; $i++) {
> %hash = $kv[$i] => $kv[$i + 1];
> $i++;
> }
>
> while ( ($key, $value) = each %hash ) {
> print "$key +> $value\n";
> }



John
--
Any intelligent fool can make things bigger and
more complex... It takes a touch of genius -
and a lot of courage to move in the opposite
direction. -- Albert Einstein

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Re: move array elements to hash

At 12:29 PM -0700 4/14/11, mark baumeister wrote:
>Hi,
>I am trying to move array elements (populated from the ) into a
>hash
>as pairs [i] and [i + 1] and then print them out using the code below.
>If I enter "bob" as the first element and hit enter I get the
>error messages below. I guess there are multiple problems with my
>code.
>For one it appears that my $kv variable is supposed to take numeric
>values. I'm not sure if this is the reason the program aborts once
>I hit enter after my first entry (i.e. "bob").
>Any hints on why I my $kv varible is expected to be numeric
>or any other obvious problems with my code?
>
>Thanks,
>M
>
>
>Useless use of array element in void context at L2_Q9.pl line 23.
>input key/value pairs: first a key then return, then a value then
>return, etc. To stop entering key/value pairs type 'stop'
>jim
>Argument "stop" isn't numeric in numeric eq (==) at L2_Q9.pl line 17,
> line 1.
>Argument "jim" isn't numeric in numeric eq (==) at L2_Q9.pl line 17,
> line 1.
>Odd number of elements in hash assignment at L2_Q9.pl line 23,
>line 1.
>Use of uninitialized value in concatenation (.) or string at L2_Q9.pl
>line 28, line 1.
>jim +>
>
>
>#!/usr/bin/perl -w
>use strict;
>
>my %hash;
>my $kv;
>my @kv;
>my @v;
>my $i;
>my $key;
>my $value;
>
>#create key - value pairs to go into a hash by first entering each
>into a list @k or @v
>print "input key/value pairs: first a key then return, then a value
>then return, etc. To stop entering key/value pairs type 'stop'\n";
>while ($kv = ) {
> chomp($kv);
> push(@kv, $kv);
> last if ($kv == "stop");


You should reverse the order of the above two lines. You should be
testing $kv for 'stop' BEFORE pushing it onto the array. Otherwise,
you are left with 'stop' as the last element of the array, probably
not what you want.

>}
>
># move each key or value located at each index of array @kv into a
>hash so that they pair up e.g. $kv[i] with $kv[i +1] etc.
>
>for($i = 0; $i < $#kv + 1; $i++) {
> %hash = $kv[$i] => $kv[$i + 1];

You are overwriting the hash each iteration through the loop. Add
elements to your hash this way:
$hash{$kv[$i]} = $kv[$i+1];

> $i++;

You can put '$i += 2' in your for loop statement instead of $i++ and
eliminate this line.

>}

Or you can just try this:

%hash = @kv;

>
>while ( ($key, $value) = each %hash ) {
> print "$key +> $value\n";
>}


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