Array.any? / all? / none? / count

# Returns true if at least one element satisfies the condition.
array.any? { |element| condition }
array.any?  # Returns true if the array has at least one element

# Returns true if all elements satisfy the condition.
array.all? { |element| condition }
array.all?  # Returns true if no element is nil or false

# Returns true if no element satisfies the condition.
array.none? { |element| condition }

# Returns the number of elements matching the condition.
array.count
array.count(value)
array.count { |element| condition }

scores = [65, 82, 91, 78, 55]

# Use any? to check if at least one element satisfies the condition.
puts scores.any? { |s| s >= 90 }   # true (91 exists)
puts scores.any? { |s| s >= 100 }  # false

# Use all? to check if all elements satisfy the condition.
puts scores.all? { |s| s >= 50 }   # true (everyone is 50 or above)
puts scores.all? { |s| s >= 80 }   # false

# Use none? to check if no element satisfies the condition.
puts scores.none? { |s| s < 50 }   # true (no one is below 50)
puts scores.none? { |s| s > 90 }   # false (91 exists)

# Use count to count elements.
puts scores.count            # 5 (total elements)
puts scores.count(82)        # 1 (elements equal to 82)
puts scores.count { |s| s >= 80 }  # 2 (elements 80 or above)

# Practical example: validation check.
email_list = ["a@example.com", "b@example.com", "invalid-email"]
all_valid = email_list.all? { |m| m.include?("@") }
puts all_valid  # false

invalid_count = email_list.count { |m| !m.include?("@") }
puts "Invalid emails: #{invalid_count}"  # Invalid emails: 1

These methods let you write concise condition checks across an entire array. They improve readability compared to using an each loop with a flag variable.

all? always returns true for an empty array (based on the mathematical concept that a universal statement over an empty set is vacuously true). If the behavior on empty arrays matters for your use case, check with empty? first.

To extract elements that match a condition, use select / reject. To simply check for the presence of a value, include? is also available.