How to sort array of hashes by value?

Question

I'm trying to sort an array of hashes based on the given key-value, and will return that value on top of the array first, then preceded by the remaining data.

Example would be:

students = [{name: "John Doe", age: 16, adviser: "Mrs. Robinson"},
            {name: "John Smith", age: 18, adviser: "Mrs. Williams"},
            {name: "Michael Rodriguez", age: 17, adviser: "Mr. Lee"}]

def sort_by_adviser(data, name)
  ...
end

> sort_by_adviser(students, "Mr. Lee")
=> [{name: "Michael Rodriguez", age: 17, adviser: "Mr. Lee"},
    {name: "John Doe", age: 16, adviser: "Mrs. Robinson"},
    {name: "John Smith", age: 18, adviser: "Mrs. Williams"}]

> sort_by_adviser(students, "Mrs. Williams")
=> [{name: "John Smith", age: 18, adviser: "Mrs. Williams"},
    {name: "Michael Rodriguez", age: 17, adviser: "Mr. Lee"},
    {name: "John Doe", age: 16, adviser: "Mrs. Robinson"}]

Here the output brings the adviser's name on top of the list, then preceded by other hashes in the array.

> sort_by_keyvalue(data, "Z")
=> [{letter: 'Z'},
    {letter: 'A'},
         .
         .
         .
    {letter: 'Y'}]

> sort_by_keyvalue(data, 5)
=> [{number: 5, value: 'value1'},
    {number: 5, value: 'value2'},
    {number: 5, value: 'value3'},
    {number: 9, value: 'value1'},
    {number: 9, value: 'value2'},
    {number: 8, value: 'value1'},
    {number: 8, value: 'value2'},
    {number: 7, value: 'value1'},
    {number: 6, value: 'value1'},
    {number: 4, value: 'value1'},
    {number: 3, value: 'value1'},
    {number: 2, value: 'value1'},
    {number: 1, value: 'value1'},
    {number: 1, value: 'value2'},
    {number: 0, value: 'value1'}]

Anyone knows how to do it?

do you want to do any sorting, or just to move the matched one to the first place? — davidrac
– davidrac, Commented Aug 3, 2012 at 19:39
move the matched on in the first place, then do a sort_by { |k,v| k[:key] } to sort the remaining hash in the array. — JB Juliano
– JB Juliano, Commented Aug 3, 2012 at 19:48

Pritesh Jain · Accepted Answer · 2012-08-03 20:21:25Z

3

Another implemention :)

def sort_by_adviser(data, name)
    data.each_with_index do |hash,index|
      if hash[:adviser]==name
         data.delete_at index #delete from array
         data.unshift hash
         break
      end
    end
   data
end

 > sort_by_adviser(students, "Mr. Lee")  
 #=> [{:name=>"Michael Rodriguez", :age=>17, :adviser=>"Mr. Lee"}, {:name=>"John Doe", :age=>16, :adviser=>"Mrs. Robinson"}, {:name=>"John Smith", :age=>18, :adviser=>"Mrs. Williams"}]

answered Aug 3, 2012 at 20:21

Pritesh Jain

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Abe Voelker · Accepted Answer · 2012-08-03 19:49:04Z

2

def creamy_sort(key, value, arr)
  top, bottom = arr.partition{|e| e[key] == value }
  top.concat(bottom.sort{|a,b| b[key] <=> a[key]})
end

creamy_sort(:adviser, "Mr. Lee", students)

answered Aug 3, 2012 at 19:49

Abe Voelker

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Comments

davidrac · Accepted Answer · 2012-08-03 19:52:52Z

1

You can do that:

def sort_by_adviser(data, name)
  data = data.sort{|x,y|x[:adviser] <=> y[:adviser]}
  i = data.index{|h|h[:adviser] = name}
  h = data.delete_at i
  data.unshift h
end

edited Aug 3, 2012 at 19:52

answered Aug 3, 2012 at 19:47

davidrac

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Comments

knut · Accepted Answer · 2012-08-03 19:52:08Z

I have this solution:

students = [{name: "John Doe", age: 16, adviser: "Mrs. Robinson"},
            {name: "John Smith", age: 18, adviser: "Mrs. Williams"},
            {name: "Michael Rodriguez", age: 17, adviser: "Mr. Lee"}]

def sort_by_adviser(data, *name)
  data.sort_by{| entry |    
    [ 
      name.index(entry[:adviser]) || 999,
      entry[:age], entry[:name] #2nd sort criteria
    ]
  }
end

p sort_by_adviser(students, "Mr. Lee")
#[{:name=>"Michael Rodriguez", :age=>17, :adviser=>"Mr. Lee"}, {:name=>"John Doe", :age=>16, :adviser=>"Mrs. Robinson"}, {:name=>"John Smith", :age=>18, :adviser=>"Mrs. Williams"}]

p sort_by_adviser(students, "Mrs. Williams")
# [{:name=>"John Smith", :age=>18, :adviser=>"Mrs. Williams"}, {:name=>"John Doe", :age=>16, :adviser=>"Mrs. Robinson"}, {:name=>"Michael Rodriguez", :age=>17, :adviser=>"Mr. Lee"}]

I didn't understand, what's the sorting of the remaining entry.

You wrote: then preceded by the remaining data. What's tho order criteria of the hash?

I selected age, followed by name. But you may adapt it for your need.

Anthony Alberto · Accepted Answer · 2012-08-03 20:03:44Z

1

def weird_sort(array, key, value)
  return array.sort_by{|d| 2 <=> (d[key] == value).object_id}
end

This is based on the fact that true.object_id equals 2 in ruby. Kind of a weird solution that's why it's a weird_sort :p It also messes around the other value ordering ... so it only guarantees you that values that are equal go on top!

answered Aug 3, 2012 at 20:03

Anthony Alberto

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