In Julia, the value of a key in a hash (also known as a dictionary) can be obtained by using the square brackets [] with the key name as the index. Here is an example:
# Creating a hash with key-value pairs
julia> my_dict = Dict("apple" => 2, "orange" => 5, "banana" => 1)
Dict{String, Int64} with 3 entries:
"orange" => 5
"apple" => 2
"banana" => 1
# Getting the value of a specific key
julia> my_dict["orange"]
5
In the example above, we create a dictionary or a hash using the Dict() function with three key-value pairs. Then, to access the value of a specific key, we use the square brackets [] with the key name as the index - in this case "orange". The output is the value associated with this key, which is 5.
If the key does not exist in the hash, an error will be thrown. To prevent this from happening, we can use the get() function instead, which returns a default value if the key is not found. Here's an example:
# Using get() function to get the value of a key
julia> my_dict = Dict("apple" => 2, "orange" => 5, "banana" => 1)
Dict{String, Int64} with 3 entries:
"orange" => 5
"apple" => 2
"banana" => 1
julia> get(my_dict, "grape", 0)
0
In this example, we use the get() function to try to get the value associated with "grape". Since this key does not exist in our dictionary, it returns the default value of 0.