rspec expect compare two hash that by excluding specified keys

Question

Is there any spec expect which will compare two hashes by excluding specified keys alone.

H1 = {'name' => 'XXXXx', 'age' => 29, 'DOB' => 'dd/mm/yyyy'}
H2 = {'name' => 'XXXXX', 'age' => 29, 'DOB' => 'dd/mm/yyyy'}

Compare the above two hashes by excluding DOB key alone.

[`Hash#values_at`](https://ruby-doc.org/core/Hash.html#method-i-values_at) and `match_array` expectation? — Aleksei Matiushkin, Mar 29 '19 at 09:47
values_at will return an array of values based on the keys specified in values_at. But I want to exclude specific set of keys alone — Munish Prabhu, Mar 29 '19 at 09:51
Names are different (`"XXXXX"` and `"XXXXx"`)? Or is this typo? — mechnicov, Mar 29 '19 at 12:02
No it's deliberated. Henceforth I should get a result as Name is differing in H2 when comparing with H1 — Munish Prabhu, Mar 30 '19 at 18:06
Or can anyone suggest me a better solution(or approach) to compare two hashes? Hash may also contain array in value. It would be nice to have the hash in the result which may contain all mismatch keys along with values when comparing H1 with H2 — Munish Prabhu, Mar 30 '19 at 19:53

mechnicov · Answer 1 · 2019-03-29T13:29:50.737

2

I don't understand why do you need so, but you can use Hash#delete_if

RSpec.describe do
  let(:hash1) { {'name' => 'XXXXX', 'age' => 29, 'DOB' => 'dd/mm/yyyy'} }
  let(:hash2) { {'name' => 'XXXXX', 'age' => 29, 'DOB' => 'dd/mm/yyyy'} }

  it 'should correctly compare two subhashes' do
    expect(hash1.delete_if { |k,_| k == 'DOB' }).to eql(hash2.delete_if { |k,_| k == 'DOB' })
  end
end

If you want to make your expect more neatly you can convert hashes before.

Also you can use Hash#reject

RSpec.describe do
  it 'should correctly compare two subhashes' do
    hash1 = {'name' => 'XXXXX', 'age' => 29, 'DOB' => 'dd/mm/yyyy'}
    hash2 = {'name' => 'XXXXX', 'age' => 29, 'DOB' => 'dd/mm/yyyy'}
    hash1, hash2 = [hash1, hash2].map { |h| h.reject { |k,_| k == 'DOB' } }

    expect(hash1).to eql(hash2)
  end
end

edited Mar 29 '19 at 13:29

answered Mar 29 '19 at 10:58

mechnicov

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I think you mistook 'DOB' for 'name'. – sawa Mar 29 '19 at 11:50
@sawa, thanks. I noticed the names are different (`"XXXXX"` and `"XXXXx"`) and misled myself.. – mechnicov Mar 29 '19 at 12:01
Wouldn't it be handy to have a hash method `delete2`, such that `{ a:1, b:2, c:3, d:4 }.delete2(:b, :d) #=> { a:1, c:3 }` without mutating the receiver? – Cary Swoveland Mar 29 '19 at 20:55
@CarySwoveland Good idea. Looks beautiful. Maybe someday appear in Ruby. – mechnicov Mar 29 '19 at 21:14

Cary Swoveland · Answer 2 · 2019-03-29T21:11:39.517

1

Rather than comparing two temporary hashes that equal H1 and H2 with the key 'DOB' (if present) removed, one could compare two temporary hashes that have keys 'DOB' with the same value. That value is arbitrary; I've used nil.

expect(H1.merge('DOB'=>nil).to eq(H2.merge('DOB'=>nil)))

Another way is:

expect((H1.keys|H2.keys).all? do |k| 
  k=='DOB' || (H1.key?(k) && H2.key?(k) && H1[k]==H2[k])
end.to eq(true)

H1.key?(k) && H2.key?(k) is there in case one of the hashes has a key k with value nil and the other hash does not have a key k.

This has the redeeming feature that it has a more modest memory requirement than do the two approaches I mentioned above.

edited Mar 29 '19 at 21:11

answered Mar 29 '19 at 16:38

Cary Swoveland

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The assymmetry decreases the beauty. I think you can just merge `{'DOB' => nil}` to both hashes. – sawa Mar 29 '19 at 19:25
@sawa, agreed. I made the change. Thanks. – Cary Swoveland Mar 29 '19 at 19:53
You got to switch the receiver and the argment for merge regarding H1. Otherwise, if H1 had a value for DOB other than nil, ... – sawa Mar 29 '19 at 20:06
1

Let's hope I finally have it right. :-) (Note my smileys have noses.) – Cary Swoveland Mar 29 '19 at 20:41

rspec expect compare two hash that by excluding specified keys

2 Answers2