How to sort a mixed array by different elements in Ruby?

Question

I have an array similar to this:

a = [
  [0, {:a=>"31", :b=>"21"}],
  [1, {:a=>"32", :b=>"11"}],
  [1, {:a=>"25", :b=>"19"}],
  [0, {:a=>"12", :b=>"10"}]
]

And I want to sort it by the first element of each row or by the various elements of the hash (2nd element in the row).

Answer 1

to sort by the first item in the Array:

> a.sort_by{|x| x.first}
 => [[0, {:a=>"31", :b=>"21"}], 
     [0, {:a=>"12", :b=>"10"}], 
     [1, {:a=>"32", :b=>"11"}], 
     [1, {:a=>"25", :b=>"19"}]] 

to sort by the first item in the Hash:

> a.sort_by{|x| x.last.first}
 => [[0, {:a=>"12", :b=>"10"}],
     [1, {:a=>"25", :b=>"19"}], 
     [0, {:a=>"31", :b=>"21"}], 
     [1, {:a=>"32", :b=>"11"}]] 

or you could sort by a given key of the hash:

> sort_key = :b
> a.sort_by{|x| x.last[ sort_key ]}
 => [[0, {:a=>"12", :b=>"10"}],
     [1, {:a=>"32", :b=>"11"}],
     [1, {:a=>"25", :b=>"19"}],
     [0, {:a=>"31", :b=>"21"}]] 

If you want to sort by the first array value, and then by the first entry in the hash, as a secondary search criteria, the answer is:

> a.sort_by{|x| [x.first, x.last.first]}
 => [[0, {:a=>"12", :b=>"10"}], 
     [0, {:a=>"31", :b=>"21"}], 
     [1, {:a=>"25", :b=>"19"}], 
     [1, {:a=>"32", :b=>"11"}]]