Ruby中嵌套哈希数组的输出处理及数据修改问题求助

Hey there! Let's work through these three tasks together—since you're a Ruby beginner, I'll break each step down clearly and point out common pitfalls that might be causing those "undefined method" errors you're seeing.

First, let's fix up your sample data to be valid Ruby (the unquoted stock symbols like GOOG would trigger a constant error otherwise):

companies = [
  {"id"=>"1", "properties"=>{"name"=>"Google", "stock_symbol"=>"GOOG", "primary_role"=>"company"}},
  {"id"=>"2", "properties"=>{"name"=>"Facebook", "stock_symbol"=>"FB", "primary_role"=>"company"}}
]

1. Output each company's name, ID, and stock symbol #

The key here is accessing the nested hash values correctly. Since these are string-keyed hashes (not Ruby objects), you need to use bracket notation (["key"]) instead of dot syntax (like company.id). Here's how to do it:

companies.each do |company|
  # Pull values from the nested hashes
  id = company["id"]
  name = company["properties"]["name"]
  stock_symbol = company["properties"]["stock_symbol"]
  
  # Format and print the result
  puts "#{name} - #{id} - #{stock_symbol}"
end

This will output:

Google - 1 - GOOG
Facebook - 2 - FB

If you were getting "undefined method" errors here, it's likely because you tried using dot syntax (e.g., company.id) instead of company["id"].

2. Remove the "primary_role" key-value pair from all companies #

You have two options here: modify the original array, or create a new array with the changes (safer if you want to keep the original data intact).

Option 1: Modify the original array

Use delete to remove the key directly from the properties hash:

companies.each do |company|
  company["properties"].delete("primary_role")
end

Option 2: Create a new array (no changes to original data)

Use map to generate a new array, and reject to filter out the unwanted key (pure Ruby, no extra libraries needed):

updated_companies = companies.map do |company|
  # Make a copy of the company hash to avoid modifying the original
  new_company = company.dup
  # Create a new properties hash without "primary_role"
  new_company["properties"] = company["properties"].reject { |key, _value| key == "primary_role" }
  new_company
end

3. Add an "industry" key-value pair to each company #

Again, use bracket notation to add the new key to the properties hash. You can set a static value, or use logic to assign different industries based on the company name:

Static industry value for all companies

companies.each do |company|
  company["properties"]["industry"] = "Technology"
end

Dynamic industry based on company name

companies.each do |company|
  industry = case company["properties"]["name"]
             when "Google" then "Internet & Software"
             when "Facebook" then "Social Media"
             else "Unknown"
             end
  company["properties"]["industry"] = industry
end

Common mistakes to avoid #

• Dot syntax vs bracket notation: Since these are plain hashes with string keys, always use ["key"] instead of .key (dot syntax works for symbol-keyed hashes or Ruby objects, not string-keyed hashes).
• Modifying original data: If you don't want to change your original array, use map and dup to create copies of the hashes before making changes.
• Nil errors: If some companies might not have a properties hash (unlikely with your API data), add a check like if company["properties"] before accessing its keys to avoid NoMethodError: undefined method [] for nil:NilClass.

内容的提问来源于stack exchange，提问作者J. Ballard