如何在 Perl 中组合哈希? [英] How can I combine hashes in Perl?

问题描述

将两个散列组合成 %hash1 的最佳方法是什么?我一直都知道 %hash2 和 %hash1 总是有唯一的键.如果可能的话，我也更喜欢一行代码.

$hash1{'1'} = 'red';$hash1{'2'} = '蓝色';$hash2{'3'} = '绿色';$hash2{'4'} = '黄色';

解决方案

Quick Answer (TL;DR)

<前>%hash1 = (%hash1, %hash2)## 要不然 ...@hash1{keys %hash2} = 值 %hash2;## 或参考...$hash_ref1 = { %$hash_ref1, %$hash_ref2 };

概述

• 上下文:Perl 5.x
• 问题:用户希望将两个哈希值¹合并为一个变量

解决方案

• 对简单变量使用上述语法
• 对复杂的嵌套变量使用 Hash::Merge

陷阱

• 当两个散列都包含一个或多个重复键时怎么办
  • (参见例如，Perl - 合并包含重复键的哈希)
  • (参见例如，Perl 哈希:如何处理重复键并获得可能的配对)
• 具有空值的键值对是否应该覆盖具有非空值的键值对?
  • 首先是什么构成空值与非空值?(例如 undef、零、空字符串、false、falsy ...)

另见

• 关于合并哈希的 PM 帖子
• PM 分类问答哈希联合
• Perl Cookbook 5.10.合并哈希
• websearch://perlfaq合并两个哈希"
• websearch://perl 合并哈希
• https://metacpan.org/pod/Hash::Merge

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脚注

¹ *(又名 associative-array，又名 字典)

What is the best way to combine both hashes into %hash1? I always know that %hash2 and %hash1 always have unique keys. I would also prefer a single line of code if possible.

$hash1{'1'} = 'red';
$hash1{'2'} = 'blue';
$hash2{'3'} = 'green';
$hash2{'4'} = 'yellow';

解决方案

Quick Answer (TL;DR)

    %hash1 = (%hash1, %hash2)

    ## or else ...

    @hash1{keys %hash2} = values %hash2;

    ## or with references ...

    $hash_ref1 = { %$hash_ref1, %$hash_ref2 };

Overview

• Context: Perl 5.x
• Problem: The user wishes to merge two hashes¹ into a single variable

Solution

• use the syntax above for simple variables
• use Hash::Merge for complex nested variables

Pitfalls

• What do to when both hashes contain one or more duplicate keys
  • (see e.g., Perl - Merge hash containing duplicate keys)
  • (see e.g., Perl hashes: how to deal with duplicate keys and get possible pair)
• Should a key-value pair with an empty value ever overwrite a key-value pair with a non-empty value?
  • What constitutes an empty vs non-empty value in the first place? (e.g. undef, zero, empty string, false, falsy ...)

See also

• PM post on merging hashes
• PM Categorical Q&A hash union
• Perl Cookbook 5.10. Merging Hashes
• websearch://perlfaq "merge two hashes"
• websearch://perl merge hash
• https://metacpan.org/pod/Hash::Merge

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Footnotes

¹ * (aka associative-array, aka dictionary)

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