Ruby two dimensional array sort based on first element

Question

I have a two dimensional array which has following structure

a = [["5/2013", 20.0, 6.0, 6.0], 
["7/2013", 73.0, 66.0, 66.0], 
["50/2013", 11530.0, 12625.27, 12087.75], 
["2/2014", 5926.0, 6058.0, 5876.4], 
["3/2013", 15.0, 0.0, 0.0], 
["4/2013", 15.0, 0.0, 0.0]]

I want to sort the array based on first element, first element of each array presents the week no in year(i.e. "2/2014" means 2nd week in 2014, which is greater than "50/2013") the result will be like this

["3/2013", 15.0, 0.0, 0.0], 
["4/2013", 15.0, 0.0, 0.0],
["5/2013", 20.0, 6.0, 6.0], 
["7/2013", 73.0, 66.0, 66.0], 
["50/2013", 11530.0, 12625.27, 12087.75], 
["2/2014", 5926.0, 6058.0, 5876.4], 
]

I tried with this one

a.sort{|a,b| a[0].split('/')[1].to_i <=> b[0].split('/')[1].to_i  && a[0].split('/')  [0].to_i <=> b[0].split('/')[0].to_i}

but it does not help. I am new in ruby and rails. Can anyone please help me to solve my problem.

If you sort as is, "2/2014" should come first and "7/2013" should come last, unlike what you have (dismissing the fact that your expected output is not a valid Ruby expression at all). Your question as is is contradictory. — sawa
– sawa, Commented Dec 10, 2013 at 9:00
It is not, @sawa. The question maker appears to want things ordered as if they where months of a given year. — paradoja
– paradoja, Commented Dec 10, 2013 at 9:17
is "50/2013" a mistake or does the 50 mean week of the year? — benjaminjosephw
– benjaminjosephw, Commented Dec 10, 2013 at 9:20
@paradoja That could not be the case. There is no month 50. You are absolutely wrong. — sawa
– sawa, Commented Dec 10, 2013 at 10:09

Santhosh · Accepted Answer · 2013-12-10 09:03:22Z

10

a.sort_by {|i| i.first.split('/').map(&:to_i).reverse }

#[
#  ["3/2013", 15.0, 0.0, 0.0],
#  ["4/2013", 15.0, 0.0, 0.0],
#  ["5/2013", 20.0, 6.0, 6.0],
#  ["7/2013", 73.0, 66.0, 66.0],
#  ["50/2013", 11530.0, 12625.27, 12087.75],
#  ["2/2014", 5926.0, 6058.0, 5876.4]
#]

answered Dec 10, 2013 at 9:03

Santhosh

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3 Comments

Saleh Enam Shohag Over a year ago

Thanks. It is exactly the answer i was looking

Liping Huang Over a year ago

Pretty cool, but what's the exact meaning of &:to_i in the map method?

Santhosh Over a year ago

@LeoHuang &:to_i is a shortcut for { |x| x.to_i }. This will give you more insight stackoverflow.com/questions/1217088/…

jvnill · Accepted Answer · 2013-12-10 09:22:41Z

2

Assuming you have a properly formed first element, meaning Date.parse will not raise any exception, use the following

>> array = [["5/2013", 20.0, 6.0, 6.0], ["7/2013", 73.0, 66.0, 66.0], ["50/2013", 11530.0, 12625.27, 12087.75], ["2/2014", 5926.0, 6058.0, 5876.4], ["3/2013", 15.0, 0.0, 0.0], ["4/2013", 15.0, 0.0, 0.0]]
>> array.sort_by { |date, _| Date.parse(date) }

To handle improperly formed date like 50/2013 (in your question), you need to decide the default value. Say you want to set the default value to today's date, change the second line to

>> array.sort_by { |date, _| Date.parse(date) rescue Date.today}

EDIT

I assumed that the first element is like a date. Looking at your question a second time leads me to believe that it isn't a date. If this isn't a date, I'll have to agree with sawa's comment. If you really want to sort this though, use the following

array.sort do |a,b|
  num1, year1 = a[0].split('/')
  num2, year2 = b[0].split('/')

  if year1 == year2
    num1.to_i <=> num2.to_i
  else
    year1.to_i <=> year2.to_i
  end
end

EDIT ignore the big method above, use Santosh's answer.

edited Dec 10, 2013 at 9:22

answered Dec 10, 2013 at 9:01

jvnill

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1 Comment

Saleh Enam Shohag Over a year ago

Thanks. Actually by 50/2013 i mean week of the year

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