How to sort an alphanumeric array in ruby reverse

Question

I want to sort an array to keep the years in ascending order and continue in the right sequence.

It is for a simple ruby application.

Suppose my array is a = [ "Influenza - 2015", "Influenza - 2019", "Influenza - 2016", "Hepatite B", "Influenza - 2018", "Influenza - 2017"]

I want my output to be:

Hepatite B
Influenza - 2019
Influenza - 2018
Influenza - 2017
Influenza - 2016
Influenza - 2015

You need to edit to change “ascending” to “descending” to be consistent with the title and example. — Cary Swoveland
– Cary Swoveland, Commented Sep 5, 2019 at 14:37

lacostenycoder · Accepted Answer · 2019-09-05 14:14:02Z

1

You can sort by regex match on numeric at end of string and fallback to string if there's no regex match, then reverse it.

a = [ "Influenza - 2015", "Influenza - 2019", "Influenza - 2016", "Hepatite B", "Influenza - 2018", "Influenza - 2017"]

puts a.sort_by{|s| s[/\d+$/] || s}.reverse

will output:

Hepatite B
Influenza - 2019
Influenza - 2018
Influenza - 2017
Influenza - 2016
Influenza - 2015

edited Sep 5, 2019 at 14:14

answered Sep 5, 2019 at 14:08

lacostenycoder

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1 Comment

demir Over a year ago

It doesn't work correctly because it's sorting by years. Try it for this array: [ "Influenza - 2015", "Influenza - 2019", "Influenza - 2016", "Hepatite B", "Influenza - 2018", "Influenza - 2017", "A - 2019", "A - 2016", "A - 2014"]

iGian · Accepted Answer · 2019-09-05 17:59:58Z

1

Option using String#split:

"Influenza - 2015".split(' - ') #=> ["Influenza", "2015"]

So,

a.sort_by{ |e| e.split(' - ').last }.reverse
#=> ["Herpes 1", "Hepatite B", "Influenza - 2019", "Influenza - 2018", "Influenza - 2017", "Influenza - 2016", "Influenza - 2015"]

edited Sep 5, 2019 at 17:59

answered Sep 5, 2019 at 17:03

iGian

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2 Comments

Cary Swoveland Over a year ago

Are you aware that herpes was first documented as a disease (by Athenaeus of Attalia) in 1 AD?

iGian Over a year ago

I didn't. But I didn't have any "Herpes 1" string in my array. It popped up from nowhere while sorting! Maybe for that! :))

Cary Swoveland · Accepted Answer · 2019-09-05 14:32:29Z

0

a.sort_by do |s|
  yr = s[/\d{4}\z/]
  yr.nil? ? [0], [1, -yr.to_i]
end

Sorting is done by pairwise comparisons of arrays using the method Array#<=>. See especially the third paragraph of the doc.

edited Sep 5, 2019 at 14:32

answered Sep 5, 2019 at 14:22

Cary Swoveland

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