Array.insert / delete / delete_at / compact

Since:		Ruby 1.8(2003)

Methods for inserting and removing elements at arbitrary positions in an array, and for removing nil values.

Syntax

array.insert(index, element, ...)

# Removes all elements matching the specified value.
array.delete(value)
array.delete(value) { return_value_if_not_found }

# Removes the element at the specified index.
array.delete_at(index)

# Returns a new array with nil elements removed.
array.compact

# Removes nil elements in place (destructive).
array.compact!

Method List

Method	Description
insert(idx, elem, ...)	Inserts one or more elements at the specified index. A negative index counts from the end of the array.
delete(val)	Removes all elements equal to the specified value and returns that value. Returns `nil` if no match is found.
delete_at(idx)	Removes the element at the specified index and returns it.
compact	Returns a new array with all `nil` elements removed. The original array is not modified.
compact!	Removes `nil` elements from the array in place. Returns the array if any changes were made, or `nil` if there was nothing to remove.

Sample Code

sample_array_insert_delete_compact.rb

members = ["member_1", "member_2", "member_3"]

# Insert "member_4" at index 1 using insert.
members.insert(1, "member_4")
puts members.inspect # ["member_1", "member_4", "member_2", "member_3"]

# Multiple elements can be inserted at once.
members.insert(2, "member_5", "member_4")
puts members.inspect # ["member_1", "member_4", "member_5", "member_4", "member_2", "member_3"]

# Remove a value using delete (removes all occurrences).
members.delete("member_4")
puts members.inspect # ["member_1", "member_5", "member_2", "member_3"]

# Use a block to specify a default return value when the element is not found.
result = members.delete("member_6") { "not found" }
puts result # not found

# Remove by index using delete_at.
removed = members.delete_at(0)
puts removed # member_1
puts members.inspect # ["member_5", "member_2", "member_3"]

# Remove nil values using compact.
data = [1, nil, 2, nil, 3, nil]
puts data.compact.inspect # [1, 2, 3]
puts data.inspect # [1, nil, 2, nil, 3, nil] (original unchanged)

# Modify the array in place using compact!.
data.compact!
puts data.inspect # [1, 2, 3]

Running the code produces the following output:

ruby array_insert_delete_compact.rb
["member_1", "member_4", "member_2", "member_3"]
["member_1", "member_4", "member_5", "member_4", "member_2", "member_3"]
["member_1", "member_5", "member_2", "member_3"]
not found
member_1
["member_5", "member_2", "member_3"]
[1, 2, 3]
[1, nil, 2, nil, 3, nil]
[1, 2, 3]

Notes

Use insert to add elements in the middle of an array. For appending to the end, push or << is faster. Use delete to remove elements by value, and delete_at to remove an element by index.

delete removes all elements that match the given value, so if the same value appears multiple times, every occurrence will be deleted. Use delete_at when you need to remove only the element at a specific position.

Use compact to clean up unwanted nil values that appear as a result of array processing. To remove duplicate elements, use uniq. For operations at the end or beginning of an array, use push / pop / shift / unshift.

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