I have a Ruby array [1, 4]. I want to insert another array [2, 3] in the middle so that it becomes [1, 2, 3, 4]. I can achieve that with [1, 4].insert(1, [2, 3]).flatten, but is there a better way to do this?
4 Answers
You could do it the following way.
[1,4].insert(1,*[2,3])
The insert() method handles multiple parameters. Therefore you can convert your array to parameters with the splat operator *.
2 Comments
Andree
All answers I got are great, but I think yours are the easiest to read. Thanks!
Cary Swoveland
It's perhaps worth noting that
[1,4].insert(2,*[2,3]) #=> [1,4,2,3], which allows the elements of the second array to be inserted after the last element of the first array.One form of the method Array#[]= takes two arguments, index and length. When the latter is zero and the rvalue is an array, the method inserts the elements of the rvalue into the receiver before the element at the given index (and returns the rvalue). Therefore, to insert the elements of:
b = [2,3]
into:
a = [1,4]
before the element at index 1 (4), we write:
a[1,0] = b
#=> [2,3]
a #=> [1,2,3,4]
Note:
a=[1,4]
a[0,0] = [2,3]
a #=> [2,3,1,4]
a=[1,4]
a[2,0] = [2,3]
a #=> [1,4,2,3]
a=[1,4]
a[4,0] = [2,3]
a #=> [1,4,nil,nil,2,3]]
which is why the insertion location is before the given index.
1 Comment
Stefan
This is a very concise way to insert another array's elements. Maybe you should add some explanation (and some whitespace).
def insert_array receiver, pos, other
receiver.insert pos, *other
end
insert_array [1, 4], 1, [2, 3]
#⇒ [1, 2, 3, 4]
or, the above might be achieved by monkeypatching the Array class:
class Array
def insert_array pos, other
insert pos, *other
end
end
I believe, this is short enough notation to have any additional syntax sugar. BTW, flattening the result is not a good idea, since it will corrupt an input arrays, already having arrays inside:
[1, [4,5]].insert 1, *[2,3]
#⇒ [1, 2, 3, [4,5]]
but:
[1, [4,5]].insert(1, [2,3]).flatten
#⇒ [1, 2, 3, 4, 5]
answered Jan 27, 2016 at 9:18
Aleksei Matiushkin
121k12 gold badges109 silver badges173 bronze badges
Comments
My option without array#insert method
array = [1,2,3,6,7,8]
new_array = [4,5]
array[0...array.size/2] + new_array + array[array.size/2..-1]
[1,1,4,4]input, should[2,3]be inserted where?