rails sort of 2 dimensional array does not work

Question

I have a 2d array which is supposed to be a user ranking, based on points. I first init it:

ranked_user = []

Then I do some points calculations and push some stuff into the array:

ranked_user.push([user.id, user.username, user.location, points])

which results in

=> [[8, "Jhonny", "Berlin", 11], [9, "Ben", "Hamburg", 3], [10, "Hugo", "Munich", 6]]

now I want to sort that array based on the 4th value (points) in order to show the ranking. I've tried two things:

ranked_user.sort_by{|k|k[3]}

and

ranked_user.sort { |a, b| b[3] <=> a[3] }

I expect this:

=> [[9, "Ben", "Hamburg", 3], [10, "Hugo", "Munich", 6], [8, "Jhonny", "Berlin", 11]]

but the array simply is not sorted.

What do I do wrong?

Somehow, if I put that into an each loop it does work. If I plot it out in plain, it remains unsorted. — DonMB
– DonMB, Commented Jul 29, 2014 at 22:54
What do you mean? You must also remember that this doesn't change the array, if that is what you want you can use sort_by! — Eyeslandic
– Eyeslandic, Commented Jul 29, 2014 at 23:00
Iceman is right, just use sort_by! or just save the sorted array to a new local variable. — Eki Eqbal
– Eki Eqbal, Commented Jul 29, 2014 at 23:03

Trip · Accepted Answer · 2014-07-29 23:31:24Z

2

Just to add on to Morgan Laco's answer :

If you do :

ranked_user.sort_by{|k|k[3]}

Then ranked_user would still be unordered. Only the return is ordered.

So in order to change ranked_user, you would have to do either of these :

ranked_user = ranked_user.sort_by{|k|k[3]}
ranked_user.sort_by!{|k|k[3]}

answered Jul 29, 2014 at 23:31

Trip

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1 Comment

ty - guess that was my mistake

Morgan Laco · Accepted Answer · 2014-07-29 23:11:01Z

2

You need to use sort_by! in order to modify the original array.

answered Jul 29, 2014 at 23:11

Morgan Laco

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