How to check if hash keys match value from array

Question

I have:

arr = ['test', 'testing', 'test123']
ht = {"test": "abc", "water": "wet", "testing": "fun"}

How can I select the values in ht whose key matches arr?

ht_new = ht.select {|hashes| arr.include? hashes}
ht_new # => "{"test": "abc", "testing": "fun"}"

Additionally, how can we return values from:

arr = ["abc", "123"]
ht = [{"key": "abc", "value": "test"}, {"key": "123", "value": "money"}, {"key": "doremi", "value": "rain"}}]
output # => [{"key": "abc", "value": "test"}, {"key": "123", "value": "money"}]

What is your code ht_new = ht.select {|hashes| arr.include? hashes} intended to stand for? Is it your failed attempt? Or are you claiming that it returns {"test": "abc", "testing": "fun"}, which is a lie, since a key-value pair is compared with arr, and furthermore, no key in ht matches arr unless you convert from string to symbol? — sawa
– sawa, Commented Jan 25, 2019 at 5:21
The second ht is not valid Ruby expression. Your second question is also not clear. — sawa
– sawa, Commented Jan 25, 2019 at 5:27

Cary Swoveland · Accepted Answer · 2019-01-24 19:38:22Z

4

Only a slight change is needed:

ht.select { |k,_| arr.include? k.to_s }
  ##=> {:test=>"abc", :testing=>"fun"}

See Hash#select.

The block variable _ (a valid local variable), which is the value of key k, signifies to the reader that it is not used in the block calculation. Some prefer writing that |k,_v|, or some-such.

answered Jan 24, 2019 at 19:38

Cary Swoveland

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iGian · Accepted Answer · 2019-01-24 21:50:45Z

2

One option is mapping (Enumerable#map) the keys in arr:

arr.map.with_object({}) { |k, h| h[k] = ht[k.to_sym] }

#=> {"test"=>"abc", "testing"=>"fun", "test123"=>nil}

If you want to get rid of pairs with nil value:

arr.map.with_object({}) { |k, h| h[k] = ht[k.to_sym] if ht[k.to_sym] }

#=> {"test"=>"abc", "testing"=>"fun"}

This is an option for the last request:

ht.select{ |h| h if h.values.any? { |v| arr.include? v} }
# or
arr.map { |e| ht.find { |h| h.values.any?{ |v| v == e } } }

#=> [{:key=>"abc", :value=>"test"}, {:key=>"123", :value=>"money"}]

edited Jan 24, 2019 at 21:50

answered Jan 24, 2019 at 19:32

iGian

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3 Comments

max pleaner Over a year ago

May be better to use reduce here because OP doesn't want the keys that aren't found in the array

iGian Over a year ago

@maxpleaner Thanks I see. I added a way to reject nil value. But I don't know how to with reduce?

iGian Over a year ago

Edit with an answer for the additional request

sawa · Accepted Answer · 2019-01-25 05:17:21Z

1

A straightforward way is:

 ht.slice(*arr.map(&:to_sym))
# => {:test => "abc", :testing => "fun"}

answered Jan 25, 2019 at 5:17

sawa

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