Rails - Aug 2005 - For Loops and the first or last element

Hey all,

A few times in my application I need to print out a comma-delimited 
list.  The easy way is something like:

<% for keyword in @keywords -%>
    <% keyword.text %>,
<% end -%>

Which would produce something like:

keyword1, keyword2, keyword3,

And that trailing comma is starting to get to me.  I hacked up a working 
solution that looks like this:

<% previous_keyword = nil -%>
<% for next_keyword in keywords -%>
  <% if previous_keyword -%>
       <%= previous_keyword.text %>,
  <% end %>
  <% previous_keyword = next_keyword -%>
<% end -%>
<%= previous_keyword.text %>

This method produces a list like:

keyword1, keyword2, keyword3

So it works, but it feels wrong.  Is there any built-in way to treat 
elements of an enumeration differently?  I would love something like:

<% for keyword in @keywords -%>
    <% keyword.text %>
    <% if @keyword.hasMoreElements %>
        ,
    <% end %>
<% end -%>

Thanks,
Jeff

<%= @keywords.map{|k| k.text}.join('','') %>

array = [''keyword1'', ''keyword2'',
''keyword3'']
array.join('', '') #=> keyword1, keyword2, keyword3

That, something very similar, should do the trick :-)

- Aaron ''Jomdom'' Ransley
- Web: www.jomdom.net
- Mail: jomdom-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org 

-----Original Message-----
From: rails-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
[mailto:rails-bounces-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org] On
Behalf Of Jeff Casimir
Sent: Thursday, August 04, 2005 10:24 AM
To: rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
Subject: [Rails] For Loops and the first or last element

Hey all,

A few times in my application I need to print out a comma-delimited 
list.  The easy way is something like:

<% for keyword in @keywords -%>
    <% keyword.text %>,
<% end -%>

Which would produce something like:

keyword1, keyword2, keyword3,

And that trailing comma is starting to get to me.  I hacked up a working 
solution that looks like this:

<% previous_keyword = nil -%>
<% for next_keyword in keywords -%>
  <% if previous_keyword -%>
       <%= previous_keyword.text %>,
  <% end %>
  <% previous_keyword = next_keyword -%>
<% end -%>
<%= previous_keyword.text %>

This method produces a list like:

keyword1, keyword2, keyword3

So it works, but it feels wrong.  Is there any built-in way to treat 
elements of an enumeration differently?  I would love something like:

<% for keyword in @keywords -%>
    <% keyword.text %>
    <% if @keyword.hasMoreElements %>
        ,
    <% end %>
<% end -%>

Thanks,
Jeff
_______________________________________________
Rails mailing list
Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
http://lists.rubyonrails.org/mailman/listinfo/rails

Jeff,
> Hey all,
> 
> A few times in my application I need to print out a comma-delimited 
> list.  The easy way is something like:
> 
> <% for keyword in @keywords -%>
>     <% keyword.text %>,
> <% end -%>
> 
> Which would produce something like:
> 
> keyword1, keyword2, keyword3,
> 
> And that trailing comma is starting to get to me.
Ruby''s Array#join method to the rescue!

<%= @keywords.collect {|k| h(k.text) }.join('', '') %>

This calls the code h(k.text) for every element of @keywords and collects that 
into a new array. The join() method is called for that array, and it outputs 
each member separated by its argument.

Jim
-- 
Jim Menard, jimm-Xhj3G7Rj6JI@public.gmane.org, http://www.io.com/~jimm
"Don''t let what you can''t do stand in the way of what you
can." -- John Wooden

Jim, Steve, and Matt,

Thanks for the responses.  I should have known better than to 
over-simplify my example.  I have used .join for simple situations like 
that and should have thought of it.  My real case, however, looks a 
little something like this:

<% for keyword in @keywords -%> 
  <%= link_to "#{keyword.keyword_readable.gsub(''
'',''&nbsp;'')}",
                { :action => ''by_keyword'',
                  :id => keyword
                },
                {
                  :class => ''keyword_forest_'' <<
keyword.magnitude.to_s
                }
   %>,
<% end -%>

Would it be best to go with Matt''s suggestion to use .each_with_index
to
do something like this:

<% @keywords.each_with_index{|keyword, index| -%> 
  <%= link_to "#{keyword.keyword_readable.gsub(''
'',''&nbsp;'')}",
                { :action => ''by_keyword'',
                  :id => keyword
                },
                {
                  :class => ''keyword_forest_'' <<
keyword.magnitude.to_s
                }
   %>
   <% unless index == @keywords.size - 1 -%>
    ,
   <% end -%>
<% } -%>

Thanks,
Jeff
> Ruby''s Array#join method to the rescue!
>
> <%= @keywords.collect {|k| h(k.text) }.join('', '')
%>
>
> This calls the code h(k.text) for every element of @keywords and 
> collects that into a new array. The join() method is called for that 
> array, and it outputs each member separated by its argument.
>
> Jim

Check out http://www.ruby-doc.org/core/classes/Enumerable.html#M001873  
each_with_index would let you detect when you are at the last keyword if 
you know how many keywords you have.

-Matt Margolis

Jeff Casimir wrote:
> Hey all,
>
> A few times in my application I need to print out a comma-delimited 
> list.  The easy way is something like:
>
> <% for keyword in @keywords -%>
>    <% keyword.text %>,
> <% end -%>
>
> Which would produce something like:
>
> keyword1, keyword2, keyword3,
>
> And that trailing comma is starting to get to me.  I hacked up a 
> working solution that looks like this:
>
> <% previous_keyword = nil -%>
> <% for next_keyword in keywords -%>
>  <% if previous_keyword -%>
>       <%= previous_keyword.text %>,
>  <% end %>
>  <% previous_keyword = next_keyword -%>
> <% end -%>
> <%= previous_keyword.text %>
>
> This method produces a list like:
>
> keyword1, keyword2, keyword3
>
> So it works, but it feels wrong.  Is there any built-in way to treat 
> elements of an enumeration differently?  I would love something like:
>
> <% for keyword in @keywords -%>
>    <% keyword.text %>
>    <% if @keyword.hasMoreElements %>
>        ,
>    <% end %>
> <% end -%>
>
> Thanks,
> Jeff
> _______________________________________________
> Rails mailing list
> Rails-1W37MKcQCpIf0INCOvqR/iCwEArCW2h5@public.gmane.org
> http://lists.rubyonrails.org/mailman/listinfo/rails

Jeff Casimir <jeff-+RlNNtFrnNmT15sufhRIGw@public.gmane.org> writes:
> <% for keyword in @keywords -%> 
>  <%= link_to "#{keyword.keyword_readable.gsub(''
'',''&nbsp;'')}",
>                { :action => ''by_keyword'',
>                  :id => keyword
>                },
>                {
>                  :class => ''keyword_forest_'' <<
keyword.magnitude.to_s
>                }
>   %>,
> <% end -%>
I''d still use join.  That''s what it''s there for.

<%= @keywords.collect { |keyword| link_to ....... }.join(", ")
%>
-- 
doug-jGAhs73c5XxeoWH0uzbU5w@public.gmane.org