就看懂一段perl代码

发布于 2024-12-21 07:52:22 字数 463 浏览 0 评论 0原文

对于以下代码段，

foreach my $Index1 (sort { $A <=> $B } keys %{$dat1->{dat1}->[$Index2]->{Vector}})
{
if($dat1->{dat1}->[$Index2]->{Vector}->{$Index1} == 2.0) { next }
    printf $sth
}

如何理解 my $Index1 (sort { $A <=> $B } keys %{$dat1->{dat1}->[$Index2]- >{Vector}}) 和($dat1->{dat1}->[$Index2]->{Vector}->{$Index1} == 2.0)

如何一块一块理解它们的底层逻辑？谢谢。

原文

With respect to the following code segment,

foreach my $Index1 (sort { $A <=> $B } keys %{$dat1->{dat1}->[$Index2]->{Vector}})
{
if($dat1->{dat1}->[$Index2]->{Vector}->{$Index1} == 2.0) { next }
    printf $sth
}

How to understand the my $Index1 (sort { $A <=> $B } keys %{$dat1->{dat1}->[$Index2]->{Vector}}) and ($dat1->{dat1}->[$Index2]->{Vector}->{$Index1} == 2.0)

How to understand their underlying logic piece by piece? Thanks.

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是伱的 2024-12-28 07:52:22

如果您将嵌套数据结构抽象出来，这会有所帮助：

my $VectorHashRef = $dat1->{dat1}->[$Index2]->{Vector};
foreach my $Index1 (sort { $A <=> $B } keys %$VectorHashRef ) {
    # This should be corrected to $a <=> $b - names are case sensitive
    if ($VectorHashRef->{$Index1} == 2.0) { 
         next;
    }
    printf $sth;
}

$dat1->{dat1}->[$Index2]->{Vector} 是访问某些数据（a hashref）位于嵌套数据结构的深处。它采用 hashref $dat1，访问哈希键 "dat1" 指向的数据结构 - 并且该键指向数组引用。您可以从带有索引 $Index2 的数组中获取值 - 该值是对下一个数据结构 (hashref) 的引用。您将该哈希值作为键 "Vector" - 这是另一个哈希引用。

现在，让我们使用 $VectorHashRef 变量为 Vector hashref 起别名（我宽松地使用了别名一词）。

现在，您正在迭代该 hashref 的键，按数字排序（有关其工作原理的详细信息，请参阅 Dan 的答案），并且对于每个键，将哈希值与 2.0 进行比较，仅在满足以下条件时才打印某些内容：值不是 2.0。

为了更好地理解这一点，您需要阅读一些 Perl 数据结构教程 - 例如 Data Structures Cookbook （又名 perldoc perldsc）

简而言之：

当您看到类似 EXPRESSION->{KEY_EXPRESSION} 的内容时，这意味着要访问该值（对于 KEY_EXPRESSION 指定的键）在哈希引用中，哈希引用是 EXPRESSION 的结果。
当您看到类似 EXPRESSION->[INDEX_EXPRESSION] 的内容时，这意味着访问数组引用中的值（对于 INDEX_EXPRESSION 指定的数组下标），数组引用是EXPRESSION 的结果。

It helps if you abstract the nested data structure away:

my $VectorHashRef = $dat1->{dat1}->[$Index2]->{Vector};
foreach my $Index1 (sort { $A <=> $B } keys %$VectorHashRef ) {
    # This should be corrected to $a <=> $b - names are case sensitive
    if ($VectorHashRef->{$Index1} == 2.0) { 
         next;
    }
    printf $sth;
}

$dat1->{dat1}->[$Index2]->{Vector} is a way to access some piece of data (a hashref) deep in a nested data structure. It takes a hashref $dat1, accesses the data structure that is pointed to by a hash key "dat1" - and that key points to an array reference. You take the value from that array with an index $Index2 - and that value is a reference to the next data structure (hashref). You take the value of that hash for the key "Vector" - which is another hashref.

Now, let's alias that Vector hashref with $VectorHashRef variable (I'm using the word alias loosely).

Now, you are iterating over the keys of that hashref, sorted numerically (see Dan's answer for details on how that works), and for each key, comparing the hash value to 2.0, printing something only if the value is NOT 2.0.

To understand this well, you need to read somee data structures in Perl tutorial - for example Data Structures Cookbook (aka perldoc perldsc)

In short:

When you see something that looks likie EXPRESSION->{KEY_EXPRESSION}, that means accessing the value (for a key specified by KEY_EXPRESSION) in a hashref, with the hash reference being the result of EXPRESSION.
When you see something that looks likie EXPRESSION->[INDEX_EXPRESSION], that means accessing the value (for a array subscript specified by INDEX_EXPRESSION) in an array reference, with the array reference being the result of EXPRESSION.

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