perl - 将唯一元素推入数组并从唯一元素创建变量

Question

我正在使用 Perl。

我从一个包含两列的制表符分隔的 txt 文件开始。

cat1    val1
cat1    val2
cat2    val3 
cat3    val4
cat1    val5
cat4    val6

我想将第 1 列中的唯一类别推送到一个数组中并创建与这些唯一类别同名的空变量

所以最后我会：

@unique_categories = ("cat1", "cat2", "cat3", "cat4");

$cat1 = '';
$cat2 = '';
$cat3 = '';
$cat4 = '';

这是我尝试过的：

#! /usr/bin/perl
use strict;
use warnings;

open(my $file,'<',"file.txt") || die ("Could not open file $!"); #input file

my $categories = '';
my @categories_unique = '';

while(<$file>){
    chomp;
    my $line = $_;
    my @elements = split ("\t", $line);
    $categories = $elements[0]; #everything seems fine until here
    push(@categories_unique, $categories) unless grep{$_ eq $categories} @categories_unique; #with this line I want to store the unique values in an array
    #here I want to create the empty variables, but don't know how to
}

Answer 1

使用动态创建名称的变量很危险，请参阅 Why it's stupid to `use a variable as a variable name' 和 A More Direct Explanation of the Problem。

在 Perl 中，您可以使用散列来保留唯一值，也可以代替未知名称的变量。它也比每次迭代整个数组要快得多。

#! /usr/bin/perl
use strict;
use warnings;

open my $fh, '<', 'file.txt' or "Could not open file $!";
my %categories;

while (my $line = <$fh>) {
    chomp $line;
    my @elements = split /\t/, $line;
    ++$categories{ $elements[0] };
}
my @categories = keys %categories;

现在，%categories 哈希值只是该类别出现的次数。例如，$categories{cat1} 是 3。如果您决定要使用每个类别的值，则只需替换

++$categories{ $elements[0] };

与

push @{ $categories{ $elements[0] } }, $elements[1];

Answer 2

第一次尝试还不错。这就是你需要的

#! /usr/bin/perl
use strict;
use warnings;

open(my $file,'<',"file.txt") || die ("Could not open file $!"); #input file

my %categories_unique = ();
my @categories_unique = ();

while(<$file>){
    chomp;
    my $line = $_;
    my @elements = split ("\t", $line);
    $categories = $elements[0]; #everything seems fine until here
    $categories_unique{$categories} = 1; # Use the fact that keys in a hash are unique
}

@categories_unique = keys %categories_unique;
{
    no strict 'refs'; # allows access to symbol table
    *{$_} = undef() foreach @categories_unique; create a symbol table entry 
}