CODEWITHSUNDEEP
ruby
rutvikpensionwar
rutvikpensionwar

Reputation: 21

How do I remove specific 'nil' values from a ruby hash?

Consider the following hash:

H = {"a" => 100, "b" => 200, "c" => nil, "d" => nil}

I want to preserve the nil value with "c", and remove the nil value with "d". How can I do that?

Applying compact will remove all nil values (i.e., with keys "c" and "d").

Question Removing all empty elements from a hash / YAML? addresses this issue, but I thought there could have been a function equivalent to .compact.

Upvotes: 1

Views: 2354

Answers (4)

Daniel
Daniel

Reputation: 11

If it is just one key, why not Hash#delete to remove the pair from the Hash instance?

h = {"a" => 100, "b" => 200, "c" => nil, "d" => nil}
h.delete("d") 
h # => {"a" => 100, "b" => 200, "c" => nil}

Upvotes: 1

Cary Swoveland
Cary Swoveland

Reputation: 110745

h = Hash["a" => 100, "b" => 200, "c" => nil, "d" => nil]

If the resulting key order is not important you could write:

h.compact.merge("c" => nil)
  #=> {"a"=>100, "b"=>200, "c"=>nil}

or

h.compact!.update("c" => nil)

if the hash is to be modified in place.

Upvotes: 1

iGian
iGian

Reputation: 11193

If I get the point, once you know that a specific key must be nil, for example "c" you could do something like:

h = {"a"=>100, "b"=>200, "c"=>nil, "d"=>nil}
h.compact!["c"] = nil

# => {"a"=>100, "b"=>200, "c"=>nil}

Now, if you call h["c"] you get nil.

Consider also that when you simply do h.compact! and call h["c"] you get nil anyway.

Upvotes: 0

tadman
tadman

Reputation: 211720

There's a method for that:

h.delete_if { |k,v| v.nil? }

Where k,v represents the key/value pair.

If you can quantify why you want the c key preserved you can incorporate that in the logic. Is it just the first nil that's saved?

If that's the case, you can try this:

count = 0
h.delete_if { |k,v| v.nil? && (count += 1) != 1 }

Note that Ruby is a case sensitive language and H is a constant by virtue of being a capital letter. For variables use lower-case only.

Additionally, the traditional way to declare a Ruby hash is:

h = { "a" => 100, "b" => 200, "c" => nil, "d" => nil }

Where that's only if you want string keys. With Symbol keys it's even more concise:

h = { a: 100, b: 200, c: nil, d: nil }

Upvotes: 2

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