在 Ruby 中动态创建多维散列
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Dynamically creating a multi-dimensional hash in Ruby
提问by Chris Allen Lane
I'm a PHP developer who's trying to gain some proficiency in Ruby. One of the projects I'm cutting my teeth on now is a source-code auditing tool that scans webapp files for potentially dangerous functions in several web programming languages. When matches are found, the script saves the relevant information in a poi(point-of-interest) class for display later on.
我是一名 PHP 开发人员，正在尝试精通 Ruby。我现在正在研究的项目之一是一个源代码审计工具，它扫描 webapp 文件以查找几种 web 编程语言中的潜在危险功能。找到匹配项后，脚本会将相关信息保存在poi（兴趣点）类中以供稍后显示。
An example instance of that class would look something like this (modeled in YAML):
该类的示例实例如下所示（以 YAML 建模）：
poi:
file_type: "php"
file: "the-scanned-file.php"
line_number: 100
match: "eval()"
snippet: "echo eval()"
On display, I want to organize these points of interest like so:
在展示时，我想像这样组织这些兴趣点：
- file_type
-- file
--- match (the searched payload)
Thus, before presentation, I'm trying to structure a flat array of poiobjects into a hash mirroring the structure above. This will allow me to simply iterate over the items in the hash to produce the desired on-screen organization. (Or at least, that's the plan.)
因此，在演示之前，我试图将poi对象的平面数组构建为反映上述结构的哈希。这将允许我简单地迭代散列中的项目以生成所需的屏幕组织。（或者至少，这是计划。）
And now, for my question: how do I do that in Ruby?
现在，对于我的问题：我如何在 Ruby 中做到这一点？
In PHP, I could do something like this really easily:
在 PHP 中，我可以很容易地做这样的事情：
<?php
$sorted_pois = array();
foreach($points_of_interest as $point){
$sorted_pois[$point->file_type][$point->file][$point->match][] = $point;
}
?>
I've tried translating that thought from PHP to Ruby like this, but to no avail:
我试过像这样将这个想法从 PHP 翻译成 Ruby，但无济于事：
sorted_pois = {}
@points_of_interest.each_with_index do |point, index|
sorted_pois[point.file_type.to_sym][point.file.to_sym][point.match.to_sym].push point
end
I've spent a few hours on this, and I'm kind of banging my head against the wall at this point, so presumably I'm way off-base. What's the proper way to handle this in Ruby?
我在这上面花了几个小时，在这一点上我的头有点撞墙，所以大概我离基地很远。在 Ruby 中处理这个问题的正确方法是什么？
Update:
更新：
For reference, this is the precise method I have defined:
作为参考，这是我定义的精确方法：
# sort the points of interest into a structured hash
def sort
sorted_pois = {}
@points_of_interest.each_with_index do |point, index|
sorted_pois[point.file_type.to_sym][point.file.to_sym][point.match.to_sym].push point
end
end
This is the error I receive when I run the code:
这是我运行代码时收到的错误：
./lib/models/vulnscanner.rb:63:in `sort': undefined method `[]' for nil:NilClass (NoMethodError)
from /usr/lib/ruby/1.8/rubygems/custom_require.rb:31:in `each_with_index'
from ./lib/models/vulnscanner.rb:62:in `each'
from ./lib/models/vulnscanner.rb:62:in `each_with_index'
from ./lib/models/vulnscanner.rb:62:in `sort'
from ./webapp-vulnscan:69
Line 62 (as you can likely infer) is this line in particular:
第 62 行（您可能会推断出）特别是这一行：
@points_of_interest.each_with_index do |point, index|
As an additional reference, here's what (a snippet of) @points_of_interestlooks like when converted to YAML:
作为附加参考，以下是@points_of_interest转换为 YAML 时的（片段）外观：
- !ruby/object:PoI
file: models/couponkimoffer.php
file_type: php
group: :dangerous_functions
line_number: "472"
match: `
snippet: ORDER BY `created_at` DESC
- !ruby/object:PoI
file: models/couponkimoffer.php
file_type: php
group: :dangerous_functions
line_number: "818"
match: `
snippet: WHERE `company_slug` = '$company_slug'
- !ruby/object:PoI
file: models/couponkimoffer.php
file_type: php
group: :dangerous_functions
line_number: "819"
match: `
snippet: ORDER BY `created_at` DESC
回答by Phrogz
@John's Enumerable#group_bysuggestion is one good way to solve your needs. Another would be to create an auto-vivifying Hash (like you appear to have in PHP) like so:
@John 的Enumerable#group_by建议是解决您需求的一种好方法。另一种方法是创建一个自动激活的哈希（就像你在 PHP 中的样子），如下所示：
hash = Hash.new{ |h,k| h[k] = Hash.new(&h.default_proc) }
hash[:a][:b][:c] = 42
p hash
#=> {:a=>{:b=>{:c=>42}}}
Note that this sort of auto-vivification can be 'dangerous' if you access keys that don't exist, as it creates them for you:
请注意，如果您访问不存在的密钥，这种自动激活可能是“危险的”，因为它会为您创建它们：
p hash["does this exist?"]
#=> {}
p hash
#=> {:a=>{:b=>{:c=>42}}, "does this exist?"=>{}}
You can still use the vivifying default_procwithout hitting this danger if you use key?to test for the key first:
default_proc如果您先用于key?测试密钥，您仍然可以使用 viviifying而不会遇到这种危险：
val = hash["OH NOES"] if hash.key?("OH NOES")
#=> nil
p hash
#=> {:a=>{:b=>{:c=>42}}, "does this exist?"=>{}}
FWIW, the error you are getting says, "Hey, you put []after something that evaluated to nil, and nildoesn't have a []method."Specifically, your code...
FWIW，你得到的错误说，“嘿，你把[]评估为 的东西放在后面nil，并且nil没有[]方法。” 具体来说，您的代码...
sorted_pois[point.file_type.to_sym]
evaluated to nil(because the hash did not yet have a value for this key) and then you attempted to ask for
评估为nil（因为散列还没有这个键的值），然后你试图要求
nil[point.file.to_sym]
回答by John Ledbetter
You might be interested in group_by.
您可能对group_by感兴趣。
Sample usage:
示例用法：
birds = ["Golden Eagle", "Gyrfalcon", "American Robin",
"Mountain BlueBird", "Mountain-Hawk Eagle"]
grouped_by_first_letter = birds.group_by { |s| s[0] }
# { "G"=>["Golden Eagle", "Gyrfalcon"], "A"=>["American Robin"],
# "M"=>["Mountain BlueBird", "Mountain-Hawk Eagle"] }
回答by Lukas Stejskal
The obvious problem with the example above is that nested hashes and arrays you try to use don't exist. Try this:
上面示例的明显问题是您尝试使用的嵌套散列和数组不存在。尝试这个：
sorted_pois = {}
pois.each do |point|
# sanitize data - convert to hash of symbolized keys and values
poi = Hash[ %w{file_type file match}.map do |key|
[key.to_sym, point.send(key).to_sym]
end ]
# create nested hash/array if it doesn't already exist
sorted_pois[ poi[:file_type] ] ||= {}
sorted_pois[ poi[:file_type] ][ poi[:file] ] ||= {}
sorted_pois[ poi[:file_type] ][ poi[:file] ][ poi[:match] ] ||= []
sorted_pois[ poi[:file_type] ][ poi[:file] ][ poi[:match] ] << point
end
