How to Filter a Map Based on Keys in Ruby

How to Filter a Map Based on Keys in Ruby ?

Answer

To filter a hash based on keys in Ruby, you can use the `select` method to create a new hash containing only the key-value pairs that meet the filter criteria. This method allows you to create a subset of the original hash based on specific key conditions.

✐ Examples

1 Filtering a Hash Based on Key Range

We can filter a hash based on a range of keys in Ruby by using the `select` method to create a new hash containing only the key-value pairs that fall within the specified range.

For example,

We start by declaring and initializing a hash named my_hash with some key-value pairs. In this example, the hash has integer keys and string values.
We use the select method to filter the hash based on the specified key range.
We print the filtered hash to the console using the puts function to verify the filtering.

Ruby Program

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

# Define the key range
lower_bound = 2
upper_bound = 4

# Filter the hash based on the key range
filtered_hash = my_hash.select { |k, _| k >= lower_bound && k <= upper_bound }

# Print the filtered hash
puts 'Filtered Hash by Key Range:'
filtered_hash.each { |key, value| puts "#{key}: #{value}" }

Output

Filtered Hash by Key Range:
2: two
3: three
4: four

2 Filtering a Hash Based on Specific Keys

We can filter a hash based on specific keys in Ruby by using the `select` method to create a new hash containing only the key-value pairs that match the specified keys.

For example,

We start by declaring and initializing a hash named my_hash with some key-value pairs. In this example, the hash has integer keys and string values.
We define a set of specific keys that we want to filter the hash by.
We use the select method to filter the hash based on the specified keys.
We print the filtered hash to the console using the puts function to verify the filtering.

Ruby Program

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

# Define the specific keys to filter by
keys_to_filter = [1, 3, 5]

# Filter the hash based on the specific keys
filtered_hash = my_hash.select { |k, _| keys_to_filter.include?(k) }

# Print the filtered hash
puts 'Filtered Hash by Specific Keys:'
filtered_hash.each { |key, value| puts "#{key}: #{value}" }

Output

Filtered Hash by Specific Keys:
1: one
3: three
5: five

3 Filtering a Hash with String Keys Based on Prefix

We can filter a hash with string keys based on a specific prefix in Ruby by using the `select` method to create a new hash containing only the key-value pairs that have keys starting with the given prefix.

For example,

We start by declaring and initializing a hash named my_hash with some key-value pairs. In this example, the hash has string keys and string values.
We define a prefix string that we want to filter the hash by.
We use the select method to filter the hash based on the specified prefix.
We print the filtered hash to the console using the puts function to verify the filtering.

Ruby Program

my_hash = { 'apple' => 'fruit', 'banana' => 'fruit', 'carrot' => 'vegetable', 'apricot' => 'fruit', 'blueberry' => 'fruit' }

# Define the prefix to filter by
prefix = 'ap'

# Filter the hash based on the prefix
filtered_hash = my_hash.select { |k, _| k.start_with?(prefix) }

# Print the filtered hash
puts 'Filtered Hash by Prefix:'
filtered_hash.each { |key, value| puts "#{key}: #{value}" }

Output

Filtered Hash by Prefix:
apple: fruit
apricot: fruit

Summary

In this tutorial, we learned How to Filter a Map Based on Keys in Ruby language with well detailed examples.

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How to Filter a Map Based on Keys in Ruby