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]]
7 Answers
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]
1 Comment
Philip Mutua
suppose you have to push a million items this would not be a good idea.
Using += operator:
arr = [1]
arr += [2, 3]
arr
# => [1, 2, 3]
1 Comment
Barry Kelly
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.You can do also as below using Array#concat:
arr = [1]
arr.concat([2, 3]) # => [1, 2, 3]
Comments
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:
- Array in Ruby 1.9.3: http://ruby-doc.org/stdlib-1.9.3/libdoc/csv/rdoc/Array.html
- Array in Ruby 2.0.0: http://www.ruby-doc.org/core-2.0.0/Array.html
Comments
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]
Comments
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"]
2 Comments
the Tin Man
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.Barry Kelly
@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.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
1 Comment
Dirk von Grünigen
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.
arr.push *another_arrwill add theanother_arras flattened values (will not add an array but each value)