How to check if a specific key is present in a hash or not?

Question

I want to check whether the "user" key is present or not in the session hash. How can I do this?

Note that I don't want to check whether the key's value is nil or not. I just want to check whether the "user" key is present.

sepp2k · Accepted Answer · 2016-03-08T21:32:34.280

1124

Hash's key? method tells you whether a given key is present or not.

session.key?("user")

edited Mar 08 '16 at 21:32

answered Dec 24 '10 at 22:09

sepp2k

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nice: "string" accessor works for JSON.parse parsed objects, too :) – Bijan Aug 08 '16 at 14:32
3

This doesn't work for me, the :user method worked instead – Akash Agarwal Mar 22 '17 at 20:10
if(session["user"]) also work, but not sure about the efficiency – Katelynn ruan Oct 27 '22 at 13:22

score 341 · Answer 2 · edited Jun 12 '17 at 19:44

341

While Hash#has_key? gets the job done, as Matz notes here, it has been deprecated in favour of Hash#key?.

hash.key?(some_key)

edited Jun 12 '17 at 19:44

Andre Figueiredo

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answered Aug 21 '13 at 13:09

Bozhidar Batsov

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1

Nice reference to that change request and subsequent response from Matz. – Joshua Pinter Sep 10 '15 at 12:20
1

Does anybody know for sure? – codeforester Jan 13 '17 at 09:40
`#has_key` is actually not deprecated: https://github.com/rubocop/rubocop/issues/3224#issuecomment-226175176 – jayqui Jun 20 '23 at 17:22

installero · Answer 3 · 2022-01-25T10:41:40.697

55

Hash instance has a key? method:

{a: 1}.key?(:a)
=> true

Be sure to use the symbol key or a string key depending on what you have in your hash:

{'a' => 2}.key?(:a)
=> false

edited Jan 25 '22 at 10:41

answered Mar 13 '15 at 11:20

installero

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3

Apprently existed as early as Ruby 1.6: http://ruby-doc.com/docs/ProgrammingRuby/html/ref_c_hash.html#Hash.key_qm (perhaps earlier, dunno where to check documented) – Beni Cherniavsky-Paskin Jun 28 '16 at 14:36

score 37 · Answer 4 · edited May 25 '16 at 18:38

37

It is very late but preferably symbols should be used as key:

my_hash = {}
my_hash[:my_key] = 'value'

my_hash.has_key?("my_key")
 => false 
my_hash.has_key?("my_key".to_sym)
 => true 

my_hash2 = {}
my_hash2['my_key'] = 'value'

my_hash2.has_key?("my_key")
 => true 
my_hash2.has_key?("my_key".to_sym)
 => false

But when creating hash if you pass string as key then it will search for the string in keys.

But when creating hash you pass symbol as key then has_key? will search the keys by using symbol.

If you are using Rails, you can use Hash#with_indifferent_access to avoid this; both hash[:my_key] and hash["my_key"] will point to the same record

edited May 25 '16 at 18:38

the Tin Man

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answered Jun 17 '14 at 13:08

Abdul Baig

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If you are using Rails, you can use `Hash#with_indifferent_access` to avoid this; both `:my_key` and `"my_key"` will point to the same record – Devon Parsons Apr 06 '16 at 14:07
This is the best answer especially when you are looking for a key coming from a variable, e.g., `my_hash.has_key? my_key.to_sym` :) – q9f Dec 16 '21 at 18:44

score 9 · Answer 5 · answered Feb 07 '19 at 11:24

9

Another way is here

hash = {one: 1, two: 2}

hash.member?(:one)
#=> true

hash.member?(:five)
#=> false

answered Feb 07 '19 at 11:24

Arvind singh

1,312
15
15

score 5 · Answer 6 · answered Aug 14 '16 at 16:13

5

You can always use Hash#key? to check if the key is present in a hash or not.

If not it will return you false

hash =  { one: 1, two:2 }

hash.key?(:one)
#=> true

hash.key?(:four)
#=> false

answered Aug 14 '16 at 16:13

Deepak Mahakale

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score 4 · Answer 7 · answered Feb 04 '20 at 14:52

4

In Rails 5, the has_key? method checks if key exists in hash. The syntax to use it is:

YourHash.has_key? :yourkey

answered Feb 04 '20 at 14:52

Ahmad MOUSSA

2,729
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Antonina Sych · Answer 8 · 2023-02-02T11:00:38.743

0

h = {}
if h.respond_to?(:key?) && h.key?('text') #with respond_to method check if it's hash
   puts h['text'] 
end

edited Feb 02 '23 at 11:00

answered Feb 02 '23 at 10:44

Antonina Sych

41
4

Remember that Stack Overflow isn't just intended to solve the immediate problem, but also to help future readers find solutions to similar problems, which requires understanding the underlying code. This is especially important for members of our community who are beginners, and not familiar with the syntax. Given that, **can you [edit] your answer to include an explanation of what you're doing** and why you believe it is the best approach? – Jeremy Caney Feb 03 '23 at 00:18

How to check if a specific key is present in a hash or not?

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