Is a dictionary basically just a hash table?
Also bonus: In the Ruby code "Hash.new {0}" what is the "{0}" at the end for?
The words table, dictionary and map are often used synonymously (in the context of data structures). A hash table/hash map is one kind of table/dictionary/map.
The {0}
is a block (anonymous function) which ignores its argument and returns the number 0. The block given to Hash.new
is called to produce a default value when a key is not found in the hash map.
I.e. if I do h = Hash.new {0}
and then h["key that does not exist"]
, I get back 0, instead of nil
(which I'd get without the {0}
). Note that in this case where the default value is immutable and does not depend on the key, you don't need to use the block form of Hash.new
, you can just do Hash.new(0)
to set 0 as the default value.
In Ruby a Hash is a key, value store
h = Hash.new
h['one'] = 1
h['one'] #=> 1
h['two'] #=> nil
the {0} is a block that will be evaluated if you where to call a Key that did not exist, it's like a default value.
h = Hash.new {0}
h['one'] #=> 0
h = Hash.new {|hash,key| "#{key} has Nothing"}
h['one'] #=> "one has Nothing"
A dictionary just maps a key to a value. There are many ways to achieve this; a hash-table is one of them.
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With