Ruby sorting array order by integer in string

Question

I've got a file that I read in the values from and place into an array so I can sort them:

input.txt

#75 - Hamilton Ave.
#12A - Long Road
#12B - Long Road
#120 - Curvy Road

My ruby:

result = []
file = open("input.txt").each do | line |
  result << line
end
puts result.sort_by {|x| x.to_i}.reverse

I want to sort by the integer value in the string. However the order comes out as:

#12A - Long Road
#12B - Long Road
#120 - Curvy Road
#75 - Hamilton Ave.

Instead of:

#12A - Long Road
#12B - Long Road    
#75 - Hamilton Ave.
#120 - Curvy Road

Should I be using some sort of regex to eval the string when sorting?

Is "#" the first character of each line? If not you should edit that out. "# 123anything" will always be zero. — Cary Swoveland
– Cary Swoveland, Commented Aug 2, 2016 at 18:50
Then you want result.sort_by {|x| x[1..-1].to_i}.reverse. For example "#74 - Hamilton Ave."[1..-1] #=> "74 - Hamilton Ave.". — Cary Swoveland
– Cary Swoveland, Commented Aug 2, 2016 at 18:53
@CarySwoveland this will put 12B ahead of 12A without the reverse and with the reverse will not come out in the requested order instead result.sort_by {|x| [x[1..-1].to_i,x]} so the full string can be used as the tie breaker. — engineersmnky
– engineersmnky, Commented Aug 2, 2016 at 19:06
@engineersmnky, yes, I initially missed that, as well as the errant reversel. By the time I noticed those two things Mr. Jordan had posted his solution. — Cary Swoveland
– Cary Swoveland, Commented Aug 2, 2016 at 19:34

Jordan Running · Accepted Answer · 2016-08-02 19:12:45Z

5

Use a regular expression like /\d+/ to extract the digits from the string and to_i to turn it into an integer, e.g.:

input.each_line.sort_by {|line| line[/\d+/].to_i }

To keep 12A before 12B, return an array from the block, e.g. [ line[/\d+/].to_i, line ]. This way, if two lines have the same integer, it will order those two lines alphabetically. This assumes there will only be a # before the digits in question, and that each line will have at least one digit.

input = <<END
#75 - Hamilton Ave.
#12A - Long Road
#12B - Long Road
#120 - Curvy Road
END

result = input.each_line.sort_by do |line|
  [ line[/\d+/].to_i, line ]
end

p result
# => [ "#12A - Long Road\n",
#      "#12B - Long Road\n",
#      "#75 - Hamilton Ave.\n",
#      "#120 - Curvy Road\n" ]

Throw map(&:chomp) in there if you want to get rid of the \ns.

edited Aug 2, 2016 at 19:12

answered Aug 2, 2016 at 19:07

Jordan Running

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4 Comments

engineersmnky Over a year ago

This is precisely what I was thinking. Although instead of iteration and then map I would just go with input.split("\n").sort_by....

porterhaus Over a year ago

This worked great. @engineersmnky your previous suggestion also worked as well. Is one approach more sound than the other? Asking for future reference... I am going to mark this as answer and will upvote the answer above as well if I can do that.

Jordan Running Over a year ago

@porterhaus I often prefer each_line because it simply iterates over the lines instead of loading them all into memory as split("\n") does. In this case, however, it doesn't make a difference since sort_by will load them all into memory anyway. (Also watch out for Windows-style line endings, i.e. \r\n, when you use split.)

Cary Swoveland Over a year ago

Very nice solution!

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