How to Set a Default Value for a Key in a Map in Ruby - Step by Step Examples

How to Set a Default Value for a Key in a Map in Ruby ?

Answer

To set a default value for a key in a hash in Ruby, you can use the fetch method with a default value, or the default_proc.

✐ Examples

1 Setting a Default Value Using fetch Method

We can set a default value for a key in a hash in Ruby using the fetch method, which returns the value for a given key or a specified default value if the key is not found.

For example,

We start by declaring and initializing a hash named my_map with some key-value pairs. In this example, the hash has string keys and integer values.
We use the fetch method to set a default value for a key. The fetch method takes the key and a default value to be returned if the key is not found in the hash.
We assign the result of the fetch method to the key in the hash to set the default value.
We print the updated hash to the console using the puts function.

Ruby Program

my_map = {
    'one' => 1,
    'two' => 2,
    'three' => 3
}

# Set a default value using fetch method
my_map['four'] = my_map.fetch('four', 4)

# Print the updated hash
puts my_map

Output

{'one' => 1, 'two' => 2, 'three' => 3, 'four' => 4}

2 Setting a Default Value Using default_proc

We can set a default value for a key in a hash in Ruby using the default_proc, which sets a block to be executed when a non-existent key is accessed.

For example,

We start by declaring and initializing a hash named my_map with some key-value pairs. In this example, the hash has string keys and integer values.
We use the default_proc method to set a default value for keys. The default_proc method sets a block that returns a default value when a non-existent key is accessed.
We access a non-existent key to trigger the default_proc and set the default value.
We print the updated hash to the console using the puts function.

Ruby Program

my_map = {
    'one' => 1,
    'two' => 2,
    'three' => 3
}

# Set a default value using default_proc
my_map.default_proc = proc { |hash, key| hash[key] = 4 }
my_map['four']

# Print the updated hash
puts my_map

Output

{'one' => 1, 'two' => 2, 'three' => 3, 'four' => 4}

3 Setting Multiple Default Values Using default_proc

We can set multiple default values for keys in a hash in Ruby using the default_proc, which sets a block to be executed when non-existent keys are accessed.

For example,

We start by declaring and initializing a hash named my_map with some key-value pairs. In this example, the hash has string keys and integer values.
We use the default_proc method to set multiple default values for keys. The default_proc method sets a block that returns default values when non-existent keys are accessed.
We access non-existent keys to trigger the default_proc and set the default values.
We print the updated hash to the console using the puts function.

Ruby Program

my_map = {
    'one' => 1,
    'two' => 2,
    'three' => 3
}

# Set multiple default values using default_proc
my_map.default_proc = proc { |hash, key| hash[key] = key == 'four' ? 4 : 5 }
my_map['four']
my_map['five']

# Print the updated hash
puts my_map

Output

{'one' => 1, 'two' => 2, 'three' => 3, 'four' => 4, 'five' => 5}

Summary

In this tutorial, we learned How to Set a Default Value for a Key in a Map in Ruby language with well detailed examples.

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