66

I can easily add one element to an existing array:

arr = [1]
arr << 2
# => [1, 2]

How would I add multiple elements to my array?

I'd like to do something like arr << [2, 3], but this adds an array to my array #=> [1, [2, 3]]

davegson
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    `arr.push *another_arr` will add the `another_arr` as flattened values (will not add an array but each value) – MrYoshiji Dec 19 '13 at 16:00

7 Answers7

74

Using += operator:

arr = [1]
arr += [2, 3]
arr
# => [1, 2, 3]
falsetru
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    Note that this doesn't add to the array; it creates a new array which is a concatenation of the left and right sides, and assigns it to `arr`. – Barry Kelly Nov 13 '17 at 14:03
73

Make use of .push

arr = [1]
arr.push(2, 3)
# => [1, 2, 3]

You can also .push() all elements of another array

second_arr = [2, 3]
arr.push(*second_arr)
# => [1, 2, 3]

But take notice! without the * it will add the second_array to arr.

arr.push(second_arr)
# => [1, [2, 3]]

Inferior alternative:

You could also chain the << calls:

arr = [1]
arr << 2 << 3
# => [1, 2, 3]
davegson
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28

You can do also as below using Array#concat:

arr = [1]
arr.concat([2, 3]) # => [1, 2, 3]
Arup Rakshit
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10

There is several methods to achieve that:

array = [1, 2]

array += [3, 4] # => [1, 2, 3, 4]

# push: put the element at the end of the array
array.push([5, 6]) # =>  [1, 2, 3, 4, [5, 6]]
array.push(*[7, 8]) # => [1, 2, 3, 4, [5, 6], 7, 8]

array << 9 # => [1, 2, 3, 4, [5, 6], 7, 8, 9]

# unshift: put the element at the beginning of the array:
array.unshift(0) #=> [0, 1, 2, 3, 4, [5, 6], 7, 8, 9]

Some links:

MrYoshiji
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1

Use Array#insert can add an array to any position:

a = [1, 2, 3]
b = [4,5,6]
b.insert(0, *a)
=> [1, 2, 3, 4, 5, 6]
Fangxing
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0

just use .flatten

for example if you have this array

array = [1,2,3,4,5,6]

and you do this

array.push([123,456,789])
array.push([["abc","def"],["ghi","jkl"]])

your string would look something like 

array = [[1,2,3,4,5,6],[123,456,789],[["abc","def"],["ghi","jkl"]]]

all you need to do is

array.flatten!

and now your array would like this

array = [1,2,3,4,5,6,123,456,789,"abc","def","ghi","jkl"]
CRABOLO
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    Using `flatten` is not the preferred way to do this. Understanding how arrays are concatenated shows that using `+` or `+=` avoids the need to use `flatten` at all. `flatten` is for those times when we get arrays that we didn't generate, or were too lazy to build correctly. – the Tin Man Dec 19 '13 at 16:23
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    @theTinMan You're better off using a final `flatten` over an array of arrays built using `push` than using `+=` for every concatenation. You'll get more garbage and more copying with the latter. I'd also expect O(n^2) time from the latter, and O(n) from the former. – Barry Kelly Nov 13 '17 at 14:12
-1

One more, for building up an array with items n-times you can use the splat (AKA asterisk, *):

arr = [true] * 4           # => [true, true, true, true]

You can also use the splat for repeating multiple elements:

arr = [123,'abc'] * 3      # => [123,'abc',123,'abc',123,'abc']

Of course, you can use any array operators with that, such as +:

arr = [true] * 3 + [false] # => [true, true, true, false]

I use that in conjunction with #sample to generate random weighted results:

arr.sample                 # => true 3 out of 4 times
IAmNaN
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    I think the problem is that you didn't answer the question OP has asked? He specifically asked for adding values to an existing array, and you showed him how to create an array with repeated n elements. – Dirk von Grünigen Dec 04 '19 at 15:57