从对象数组中提取红宝石哈希元素值

Question

I've got the following array

[#<Attachment id: 73, container_id: 1, container_type: "Project", filename: "Eumna.zip", disk_filename: "140307233750_Eumna.zip", filesize: 235303, content_type: nil, digest: "9a10843635b9e9ad4241c96b90f4d331", downloads: 0, author_id: 1, created_on: "2014-03-07 17:37:50", description: "", disk_directory: "2014/03">, #<Attachment id: 74, container_id: 1, container_type: "Project", filename: "MainApp.cs", disk_filename: "140307233750_MainApp.cs", filesize: 1160, content_type: nil, digest: "6b985033e19c5a88bb5ac4e87ba4c4c2", downloads: 0, author_id: 1, created_on: "2014-03-07 17:37:50", description: "", disk_directory: "2014/03">]

I need to extract the value 73 and 74 from this string which is Attachment id.

is there any way to extract this value

Answer 1

just in case author meant he has an actual String instance:

string = '[#<Attachment id: 73, container_id: 1, container_type: "Project", filename: "Eumna.zip", disk_filename: "140307233750_Eumna.zip", filesize: 235303, content_type: nil, digest: "9a10843635b9e9ad4241c96b90f4d331", downloads: 0, author_id: 1, created_on: "2014-03-07 17:37:50", description: "", disk_directory: "2014/03">, #<Attachment id: 74, container_id: 1, container_type: "Project", filename: "MainApp.cs", disk_filename: "140307233750_MainApp.cs", filesize: 1160, content_type: nil, digest: "6b985033e19c5a88bb5ac4e87ba4c4c2", downloads: 0, author_id: 1, created_on: "2014-03-07 17:37:50", description: "", disk_directory: "2014/03">]'

string.scan(/\\sid: (\\d+)/).flatten => ["73", "74"]

Answer 2

Do as below using Array#collect :

array.collect(&:id)

In case it is a string use JSON::parse to get the array back from the string first, then use Array#collect method as below :

require 'json'
array = JSON.parse(string)
array.collect(&:id)

Answer 3

The elements of the array (I'll call it a ) look like instances of the class Attachment (not strings). You can confirm that by executing e.class in IRB, where e is any element a (eg, a.first ). My assumption is correct if it returns Attachment . The following assumes that is the case.

@Arup shows how to retrieve the values of the instance variable @id when it has an accessor (for reading):

a.map(&:id)

(aka collect ). You can see if @id has an accessor by executing

e.instance_methods(false)

for any element e of a . This returns an array which contains all the instance methods defined for the class Attachment . (The argument false causes Ruby's built-in methods to be excluded.) If @id does not have an accessor, you will need to use Object@instance_variable_get :

a.map { |e| e.instance_variable_get(:@id) }

(You could alternatively write the argument as a string: "@id" ).

If

s = '[#<Attachment id: 73, container_id: 1,..]'

in fact a string, but you neglected to enclose it in (single) quotes, then you must execute

a = eval(s)

to convert it to an array of instances of Attachment before you can extract the values of :@a .

Hear that 'click'? That was me starting my stop watch. I want to see how long it will take for a comment to appear that scolds me for suggesting the use of (the much-maligned) eval .

Two suggestions: shorten code to the essentials and avoid the need for readers to scroll horizontally to read it. Here, for example, you could have written this:

a = [#<Attachment id: 73, container_id: 1>, #<Attachment id: 74, container_id: 1>]

All the instance variables I've removed are irrelevant to the question.

If that had been too long to fit on one lines (without scrolling horizontally, write it as:

a = [#<Attachment id: 73, container_id: 1>,
     #<Attachment id: 74, container_id: 1>]

Lastly, being new to SO, have a look at this guide .