How do I sort an array of hashes by a value in the hash?

Question

This Ruby code is not behaving as I would expect:

# create an array of hashes
sort_me = []
sort_me.push({"value"=>1, "name"=>"a"})
sort_me.push({"value"=>3, "name"=>"c"})
sort_me.push({"value"=>2, "name"=>"b"})

# sort
sort_me.sort_by { |k| k["value"]}

# same order as above!
puts sort_me

I'm looking to sort the array of hashes by the key "value", but they are printed unsorted.

score 249 · Accepted Answer · edited Jul 16 '20 at 21:21

249

Ruby's sort doesn't sort in-place. (Do you have a Python background, perhaps?)

Ruby has sort! for in-place sorting, but there's no in-place variant for sort_by in Ruby 1.8. In practice, you can do:

sorted = sort_me.sort_by { |k| k["value"] }
puts sorted

As of Ruby 1.9+, .sort_by! is available for in-place sorting:

sort_me.sort_by! { |k| k["value"]}

edited Jul 16 '20 at 21:21

Nowaker

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answered Jun 30 '10 at 23:29

Stéphan Kochen

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Actually, `Array#sort_by!` is new in Ruby 1.9.2. Available today to all Ruby version by requiring my `backports` gem too :-) – Marc-André Lafortune Jul 01 '10 at 04:19
1

Hi, is there a way to sort in descending order too? I figure I might want to go `3,2,1`... – tekknolagi Oct 28 '12 at 06:53
2

You can't do that with `sort_by`, but use `sort` or `sort!` and simply flip the operands: `a.sort! {|x,y| y <=> x }` (http://www.ruby-doc.org/core-1.9.3/Array.html#method-i-sort) – Stéphan Kochen Oct 28 '12 at 10:39
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Or: `puts sorted = sort_me.sort_by{ |k,v| v }` – Zaz Jul 28 '13 at 14:51
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@tekknolagi: Just append `.reverse`. – Zaz Jul 28 '13 at 14:52
@Shtééf It is doable via both methods. – Islam Azab Oct 31 '14 at 00:35
good source of information. Thanks, your answer really help me – AMIC MING Dec 15 '15 at 18:40
For reverse you can check: https://stackoverflow.com/a/38362351/1770571 – Salma Gomaa Dec 12 '17 at 13:36

score 21 · Answer 2 · edited Jul 18 '16 at 17:01

21

As per @shteef but implemented with the sort! variant as suggested:

sort_me.sort! { |x, y| x["value"] <=> y["value"] }

edited Jul 18 '16 at 17:01

the Tin Man

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answered Jun 30 '10 at 23:41

bjg

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score 8 · Answer 3 · edited Jul 18 '16 at 17:01

8

Although Ruby doesn't have a sort_by in-place variant, you can do:

sort_me = sort_me.sort_by { |k| k["value"] }

Array.sort_by! was added in 1.9.2

edited Jul 18 '16 at 17:01

the Tin Man

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answered Nov 22 '12 at 04:10

AG_

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This "Array.sort_by! was added in 1.9.2" answer worked for me – web spider26 Nov 19 '16 at 06:02

score 2 · Answer 4 · answered Nov 13 '17 at 16:30

2

You can use sort_me.sort_by!{ |k| k["value"]}. This should work.

answered Nov 13 '17 at 16:30

Mukesh Kumar Gupta

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How do I sort an array of hashes by a value in the hash?

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