遍历数组并存储为新数组-Ruby

Question

This is simple but I can't find anything. I have an array that I want to loop through, pull up a specific attribute for each, and then store those attributes in a new array.

Basically:

• store array2 = [Array1[0].attr, Array1[2].attr, Array1[3].attr]

What I have

<% storedArray = [] %>
<% @data = current_user.data_items %>
       <% @data.each do |data_item| %>
          <% storedArray[data_item.count] = data_item.url_metric.da %>
       <% end %>

Updated:

I got it to work but in a really bad way. Suggestions?

<% array = []; i = 0 %>

   <% @data = current_user.reports[0].data_items %>
   <% @data.each do |data_item| %>
      <% array[i] = data_item.url_metric.da %>
      <% i = i+1 %>
   <% end %>
   <%= array %>

Answer 1

Check out the method collect

It returns a new array with the values created after the loop through the source array. In your problem the code would be:

# Get initial array
<% @data_items = current_user.reports[0].data_items %>

# Iterate through original array and return value to new array
<% @array = @data_items.collect do | data_item | %>
    # Process item
    <% data_item.url_metric.da %>
<% end %>

# Now your new array is ready to go.
<%= @array %>

Answer 2

Use

<% @array= current_user.data_items.map {|data_item| data_item.url_metric.da} %>

You can directly use the resulting array by using each like the following:

<% current_user.data_items.map {|data_item| data_item.url_metric.da}.each |result| %>
# Do something with the result
<% end %>

See http://www.ruby-doc.org/core-2.0/Array.html for more list operations.