Loop through an array of grouped data in ruby (rails)

Question

Say you have an ordered array like this, generated from a database of addresses:

[
  { city: Sacramento, state: CA },
  { city: San Francisco, state: CA },
  { city: Seattle, state: WA }
]

And you want to generate HTML with it like this:

<p>CA</p>
<ul>
    <li>Sacramento</li>
    <li>San Francisco</li>
</ul>
<p>WA</p>
<ul>
    <li>Seattle</li>
</ul>

So you're grouping by state. One approach to doing this would be to remember the last row on each iteration of the loop and to display the state and bookending UL tags only if the current row's state is the same as the last rows state. That seems kind of nasty and non Ruby-y.

Anyone have any advice on an elegant Ruby/Rails approach to this?

Jonas Elfström · Accepted Answer · 2011-03-23 22:01:26Z

9

Enumerable has group_by

cities = [
  { city: "Sacramento", state: "CA" },
  { city: "San Francisco", state: "CA" },
  { city: "Seattle", state: "WA" }]

cities.group_by {|c| c[:state]}


=> {"CA"=>[{:city=>"Sacramento", :state=>"CA"}, 
           {:city=>"San Francisco", :state=>"CA"}], 
    "WA"=>[{:city=>"Seattle", :state=>"WA"}]}

I'm kind of rusty on ERB but I think it would be something like this

<% @cities_by_state.each do |state, cities| %>
<p><%= state %></p>
<ul>
  <% cities.each do |city| %>
    <li><%= city[:city] %></li>
  <% end %>
</ul>
<% end %>

edited Mar 23, 2011 at 22:01

answered Mar 23, 2011 at 21:37

Jonas Elfström

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Comments

Mladen Jablanović · Accepted Answer · 2011-03-23 21:32:31Z

8

Enumerable#group_by ?

array = [
  {city: 'Sacramento', state: 'CA'},
  {city: 'San Francisco', state: 'CA'},
  {city: 'Seattle', state: 'WA'}
]

array.group_by{|elem| elem[:state]}
# => {"CA"=>[{:city=>"Sacramento", :state=>"CA"}, {:city=>"San Francisco", :state=>"CA"}], "WA"=>[{:city=>"Seattle", :state=>"WA"}]}

answered Mar 23, 2011 at 21:32

Mladen Jablanović

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Comments

Shiv · Accepted Answer · 2011-03-23 21:39:31Z

0

You can use the group_by function in Rails

@records.group_by{|x| x[:state]}

This will return you a Hash where the key is the state and the values are an array of the records

This link should help you figure out how it works a little more.

edited Mar 23, 2011 at 21:39

answered Mar 23, 2011 at 21:33

Shiv

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3 Comments

coreyward Over a year ago

You can't use Symbol#to_proc to reference a symbol hash key. ;)

Mladen Jablanović Over a year ago

@coreyward: You can if your elements are AR objects, not Hashes. ;)

coreyward Over a year ago

@Mladen Jablanović Yes, then they are methods, not symbol hash keys. Short of the missing quotation marks delimiting the hash values as strings, the question shows a valid Ruby hash definition.

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