What is the equivalent hash function of "push' arrays in perl? - arrays

Question

I am a beginner programmer who is writing a program using perl that will eventually allow me to search for name, and have it tell me the early steps. So far (with the help of many nice people on here) I have this code for array format.
#!/usr/local/bin/perl
use strict;
use warnings;
my #M_array;
my #F_array;
open (my $input, "<", 'ssbn1898.txt');
while ( <$input> ) {
chomp;
my ( $name, $id ) = split ( /,/ );
if ( $id eq "M" ) {
push ( #M_array, $name );
}
else {
push ( #F_array, $name );
}
}
close ( $input );
print 'M: ' . join("\t", #M_array) . "\n";
print 'F: ' . join("\t", #F_array) . "\n";
And I attempted to use the same code to put it into a hash.
#!/usr/local/bin/perl
use strict;
use warnings;
my %M_hash;
my %F_hash;
open (my $input, "<", 'ssbn1898.txt');
while ( <$input> ) {
chomp;
my ( $name, $id ) = split ( /,/ );
if ( $id eq "M" ) {
push ( %M_hash, $name );
}
else {
push ( %F_hash, $name );
}
}
close ( $input );
print 'M: ' . join("\t", %M_hash) . "\n";
print 'F: ' . join("\t", %F_hash) . "\n";
But I get an error on the "push" function. I would assume then that this function is just for arrays. Is there an equivalent function for a hash? And what does the "push" function really do?
Thank you all for your help
http://www.ourbabynamer.com/popular-baby-names.php?year=1898&top=1000&country=US&order=0&page=1
This is the data I am working with

Answer 1

Push adds an element to the back of an array.
#a = ( 1, 2, 3 );
push #a, 4; # #a is now ( 1, 2, 3, 4 )
Insert adds an element to a hash.
%h = ( foo => 1, bar => 2 );
$h{ qux } = 3; # %h is now ( foo => 1, bar => 2, qux => 3 );
Take a look at perldoc perlintro
http://perldoc.perl.org/perlintro.html

Answer 2

push adds an element at the end of an array. Hashes don't have an end, so there's no equivalent for hashes. You need to specify the key of the element you wish to set.
$hash{$key} = $val;
I don't know why you changed the array into a hash. It makes no sense to use a hash here. The solution is to revert your change.

Answer 3

In a comment, you say that you "must use this data as an array and a hash". I'm not really sure what you mean, but one possible interpretation is that your teacher wants you do use both hashes and arrays in your code.
One way to do that would be to store your data in an hash of arrays. It would look something like this.
#!/usr/local/bin/perl
use strict;
use warnings;
use 5.010;
my %data;
while ( <> ) { # Use <> to read from STDIN. Makes life easier :-)
chomp;
my ( $name, $gender ) = split /,/;
push #{$data{$gender}}, $name;
}
foreach (keys %data) {
say "$_: " . join("\t", #{$data{$_}_);
}
But that would involve using array references, which sounds like it might be a little advanced for your current course.
One advantage of this approach is that it will continue to work (without code changes) should you wish to add new genders to your input data!

Answer 4

push works on arrays, read more at: http://perldoc.perl.org/functions/push.html
Hashes are different than arrays, they are like associate arrays. They are un-ordered group of key-value pairs. To add some key to hash you do something like below:
my %hash = (key1 => "value1", key2 => "value2");
$hash{"key3"} = "value3";
Note that keys must be unique.
See also:
Hashes in Perl - Gabor's blog
keys - perldoc
values - perldoc

Answer 5

There is no specific function to push the element to the hash, you just need assign the value to hash key as below -
$hash{key} = 'value';
Though it will not sure that this item will be appended as the last element as the hash stores it keys in random fashion,