CODEWITHSUNDEEP
rubysortingalphabetical
user11113981
user11113981

Reputation:

Ruby: Sorting except one element

I am trying to sort string elements in array. Let's say I want to sort it [b, e, f, t, g], but want to keep e in first in ruby. So the result should be [e, b, f, g, t]. How can I write a code in ruby that sort the array that way.

Upvotes: 3

Views: 1295

Answers (4)

engineersmnky
engineersmnky

Reputation: 29373

You could partition the Array into all the "e"'s and all the not "e"'s then reduce them back together like so 

  arr = ["b", "e", "f", "t", "e","g"]
  arr.partition {|e| e == 'e'}.reduce {|e,not_e| e.concat(not_e.sort)}
  #=> ["e", "e", "b", "f", "g", "t"]

Additional credit to @iGian for 

  arr.sort.partition {|e| e == 'e'}.flatten
  #=> ["e", "e", "b", "f", "g", "t"]

Upvotes: 2

iGian
iGian

Reputation: 11193

Just to add one option more, converting to an Hash:

ary = [:b, :e, :f, :t, :g, :e]
ary.sort.group_by(&:itself).then { |h| h.delete(:e) + h.values.flatten }

It returns the array keeping all :e in front. :e must exist.

#=> [:e, :e, :b, :f, :g, :t]

The first part is returning the sorted grouping hash:

ary.sort.group_by(&:itself) #=> {:b=>[:b], :e=>[:e, :e], :f=>[:f], :g=>[:g], :t=>[:t]}

For the method to work even when :e is not present:

ary.sort.group_by(&:itself).then { |h| h.delete(:e).to_a + h.values.flatten }

Since nil.to_a #=> []

Upvotes: 1

Pragya Sriharsh
Pragya Sriharsh

Reputation: 559

You can try this: 

 arr.sort.reject{|x| x=="e"}.unshift('e')

If you have more than "e" in the array then it will ignore all 'e'.

Upvotes: 0

Cary Swoveland
Cary Swoveland

Reputation: 110685

["b", "e", "f", "t", "g"] .sort_by { |s| [s == 'e' ? 0 : 1, s] }
  #=> ["e", "b", "f", "g", "t"]

Here Enumerable#sort_by uses Array#<=> to compare each pair of elements computed by the block, such as [0, "e"] and [1, "b"]. See the third paragraph of the doc for Array#<=>.

Upvotes: 5

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