Sorting the hash in Ruby

Question

If I have an input as below:

a b 703
o z 403
l p 550
d m 650

How can I make it to work so that the list sorts by the second column that is. The above list should print

a b 703
d m 650
l p 550
o z 403

Below is my code, what I thought was I could iterate through the first column and then sort the second column by key but it doesn't seem to be working.

hash = {}
lines = file.readlines
lines.each{|line|
 if line =~ /^([A-Za-z]+) ([A-Za-z]+) (\d+)$/
   hash[$1.to_s] = {} if hash[$1.to_s] == nil
   hash[$1.to_s][$2.to_s] = $3.to_i
 end
 }


hash.each{|k,v|
array = Hash[v.sort]
array.each{|x,y|
puts "#{k} #{x} #{y}"
 }
}

The code prints as the original one. I really want to do this using hashes as I am learning hashes.

Your example is not good because it does not make difference whether it is sorted by the first column or the second. — sawa
– sawa, Commented Mar 13, 2014 at 18:02

sawa · Accepted Answer · 2014-03-13 18:05:55Z

1

lines = [
  "a b 703",
  "o z 403",
  "l p 550",
  "d m 650",
]

lines.sort_by{|l| l.scan(/\w+/)[1]}
# =>
# [
# "a b 703",
# "d m 650",
# "l p 550",
# "o z 403"
#]

answered Mar 13, 2014 at 18:05

sawa

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1 Comment

Alok Anand Over a year ago

your solution is taking 2nd column in consideration. For that it is perfect.

Alok Anand · Accepted Answer · 2014-03-13 18:47:40Z

0

As Sawa says:--

lines = [
  "a b 703",
  "o z 403",
  "l p 550",
  "d m 650",
]

case 1: sort by 1st column

lines.sort_by{|l| l.scan(/^[A-Za-z]/).first}

case 2: sort by 2nd column

lines.sort_by{|l| l.scan(/\W+[A-Za-z]/).first}

case 3: by 3rd column in descending order

lines.sort_by{|l| l.scan(/\d+$/).first.to_i}.reverse

edited Mar 13, 2014 at 18:47

answered Mar 13, 2014 at 18:40

Alok Anand

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1 Comment

Alok Anand Over a year ago

there are 4 more possibilities 1) by 1st and 2nd column, 2) by 2nd and 3rd column in descending, 3) by 1st and 3rd column in descending order and 4) by all 3 columns with 3rd column in descending order. We can ignore last 3 possibilities and work on first possibility.

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