How to sort a two-dimensional array (2d array) by date in ruby on rails?

Question

I have a two dimensional array which has following structure

array = [
          ["2019-03-11","00986587","LBP"],
          ["2019-02-23","00462421","USD"],
          ["2019-05-26","00357853","EUR"],
          ["2019-09-15","00357382","LBP"]
        ]

I want to sort the array based on the date (first element of each row).

Looking for the following result:

array = [
          ["2019-09-15","00357382","LBP"],
          ["2019-05-26","00357853","EUR"],
          ["2019-03-11","00986587","LBP"],
          ["2019-02-23","00462421","USD"]
        ]

After my research on sort and sort_by i didn't find any solution. Can anyone please help me to solve my problem ? and thank you

demir · Accepted Answer · 2019-09-17T11:14:26.037

5

You can sort 2d arrays with sort_by method: sort_by sorts in ascending order by default. If you want it to be in descending order, just reverse the result.

array.sort_by{ |a| a.first }.reverse

edited Sep 17 '19 at 11:14

answered Sep 17 '19 at 10:56

demir

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I tried it now, but it didn't work, nothing changed in the array, still having the same. @demir – iamzouz Sep 17 '19 at 11:14
@JosephNehme This code returns an array. You need to reassign the returned value to the `array` variable. Try this: `array = array.sort_by{ |a| a.first }.reverse` – demir Sep 17 '19 at 11:20
@JosephNehme If you want to mutate the current array use `sort_by!` and `reverse!` instead. – 3limin4t0r Sep 17 '19 at 11:56
1

`sort_by { |a| a.first }` could also be written as `sort_by(&:first)` – 3limin4t0r Sep 17 '19 at 11:57
2

You don't even need to use `sort_by`. Arrays are sorted by their first elements anyway (and then by their second elements, ...). – Eric Duminil Sep 17 '19 at 12:28
^ Meaning `array.sort.reverse` would be enough. – 3limin4t0r Sep 17 '19 at 12:35

score 2 · Answer 2 · answered Sep 17 '19 at 12:24

Two important notes:

your dates are written in YYYY-MM-DD format, so sorting them alphabetically will also sort them chronologically.
your dates are the first element in the arrays, and array are sorted by their first element first.

It means that all you need is:

array.sort.reverse
#=> => [["2019-09-15", "00357382", "LBP"], ["2019-05-26", "00357853", "EUR"], ["2019-03-11", "00986587", "LBP"], ["2019-02-23", "00462421", "USD"]]

If you want to save modify array in place, you can write:

array.sort!.reverse!

iGian · Answer 3 · 2019-09-17T12:12:05.380

I suggest to convert the string to a Date object and use it for sorting:

Date.strptime("2019-09-15", '%Y-%m-%d').class
#=> Sun, 15 Sep 2019

See Rails ActiveSupport Time Parsing?

So, if you want to change the original array, use Array#sort!, note the bang (!):

array.sort! { |(date_1, *rest_1), (date_2, *rest_2)| Date.strptime(date_2, '%Y-%m-%d') <=> Date.strptime(date_1, '%Y-%m-%d') }
array
#=> [["2019-09-15", "00357382", "LBP"], ["2019-05-26", "00357853", "EUR"], ["2019-03-11", "00986587", "LBP"], ["2019-02-23", "00462421", "USD"]]

Change the block for inverse order:

Date.strptime(date_1, '%Y-%m-%d') <=> Date.strptime(date_2, '%Y-%m-%d')

Note that for the block variables I used the *splat operator which works like this:

ary = [1,2,3]
a, *b = ary
p a, b
# 1
# [2, 3]

How to sort a two-dimensional array (2d array) by date in ruby on rails?

3 Answers3