somearray = ["some", "thing"]
anotherarray = ["another", "thing"]
somearray.push(anotherarray.flatten!)
I expected
["some","thing","another","thing"]
You've got a workable idea, but the #flatten!
is in the wrong place -- it flattens its receiver, so you could use it to turn [1, 2, ['foo', 'bar']]
into [1,2,'foo','bar']
.
I'm doubtless forgetting some approaches, but you can concatenate:
a1.concat a2
a1 + a2 # creates a new array, as does a1 += a2
or prepend/append:
a1.push(*a2) # note the asterisk
a2.unshift(*a1) # note the asterisk, and that a2 is the receiver
or splice:
a1[a1.length, 0] = a2
a1[a1.length..0] = a2
a1.insert(a1.length, *a2)
or append and flatten:
(a1 << a2).flatten! # a call to #flatten instead would return a new array
You can just use the +
operator!
irb(main):001:0> a = [1,2]
=> [1, 2]
irb(main):002:0> b = [3,4]
=> [3, 4]
irb(main):003:0> a + b
=> [1, 2, 3, 4]
You can read all about the array class here: http://ruby-doc.org/core/classes/Array.html
The cleanest approach is to use the Array#concat method; it will not create a new array (unlike Array#+ which will do the same thing but create a new array).
Straight from the docs (http://www.ruby-doc.org/core-1.9.3/Array.html#method-i-concat):
concat(other_ary)
Appends the elements of other_ary to self.
So
[1,2].concat([3,4]) #=> [1,2,3,4]
Array#concat will not flatten a multidimensional array if it is passed in as an argument. You'll need to handle that separately:
arr= [3,[4,5]]
arr= arr.flatten #=> [3,4,5]
[1,2].concat(arr) #=> [1,2,3,4,5]
Lastly, you can use our corelib gem (https://github.com/corlewsolutions/corelib) which adds useful helpers to the Ruby core classes. In particular we have an Array#add_all method which will automatically flatten multidimensional arrays before executing the concat.
Here are two ways, notice in this case that the first way assigns a new array ( translates to somearray = somearray + anotherarray )
somearray = ["some", "thing"]
anotherarray = ["another", "thing"]
somearray += anotherarray # => ["some", "thing", "another", "thing"]
somearray = ["some", "thing"]
somearray.concat anotherarray # => ["some", "thing", "another", "thing"]
a = ["some", "thing"]
b = ["another", "thing"]
To append b
to a
and store the result in a
:
a.push(*b)
or
a += b
In either case, a
becomes:
["some", "thing", "another", "thing"]
but in the former case, the elements of b
are appended to the existing a
array, and in the latter case the two arrays are concatenated together and the result is stored in a
.
Try this, it will combine your arrays removing duplicates
array1 = ["foo", "bar"]
array2 = ["foo1", "bar1"]
array3 = array1|array2
http://www.ruby-doc.org/core/classes/Array.html
Further documentation look at "Set Union"
Elaborating on @Pilcrow's answer the only suitable answer for huge arrays is concat
(+
) since is fast and does not allocate a new object to be garbage-collected when operating inside a loop.
Here's the benchmark:
require 'benchmark'
huge_ary_1 = Array.new(1_000_000) { rand(5_000_000..30_000_00) }
huge_ary_2 = Array.new(1_000_000) { rand(35_000_000..55_000_00) }
Benchmark.bm do |bm|
p '-------------------CONCAT ----------------'
bm.report { huge_ary_1.concat(huge_ary_2) }
p '------------------- PUSH ----------------'
bm.report { huge_ary_1.push(*huge_ary_2) }
end
Results:
user system total real
"-------------------CONCAT ----------------"
0.000000 0.000000 0.000000 ( 0.009388)
"------------------- PUSH ----------------"
example/array_concat_vs_push.rb:13:in `block (2 levels) in <main>': stack level too deep (SystemStackError)
As you can see using push
throws an ERROR: stack level too deep (SystemStackError)
when the arrays are big enough.
The question, essentially, is "how to concatenate arrays in Ruby". Naturally the answer is to use concat
or +
as mentioned in nearly every answer.
A natural extension to the question would be "how to perform row-wise concatenation of 2D arrays in Ruby". When I googled "ruby concatenate matrices", this SO question was the top result so I thought I would leave my answer to that (unasked but related) question here for posterity.
In some applications you might want to "concatenate" two 2D arrays row-wise. Something like,
[[a, b], | [[x], [[a, b, x],
[c, d]] | [y]] => [c, d, y]]
This is something like "augmenting" a matrix. For example, I used this technique to create a single adjacency matrix to represent a graph out of a bunch of smaller matrices. Without this technique I would have had to iterate over the components in a way that could have been error prone or frustrating to think about. I might have had to do an each_with_index
, for example. Instead I combined zip and flatten as follows,
# given two multi-dimensional arrays that you want to concatenate row-wise
m1 = [[:a, :b], [:c, :d]]
m2 = [[:x], [:y]]
m1m2 = m1.zip(m2).map(&:flatten)
# => [[:a, :b, :x], [:c, :d, :y]]
If the new data could be an array or a scalar, and you want to prevent the new data to be nested if it was an array, the splat operator is awesome! It returns a scalar for a scalar, and an unpacked list of arguments for an array.
1.9.3-p551 :020 > a = [1, 2]
=> [1, 2]
1.9.3-p551 :021 > b = [3, 4]
=> [3, 4]
1.9.3-p551 :022 > c = 5
=> 5
1.9.3-p551 :023 > a.object_id
=> 6617020
1.9.3-p551 :024 > a.push *b
=> [1, 2, 3, 4]
1.9.3-p551 :025 > a.object_id
=> 6617020
1.9.3-p551 :026 > a.push *c
=> [1, 2, 3, 4, 5]
1.9.3-p551 :027 > a.object_id
=> 6617020
I find it easier to push or append arrays and then flatten them in place, like so:
somearray = ["some", "thing"]
anotherarray = ["another", "thing"]
somearray.push anotherarray # => ["some", "thing", ["another", "thing"]]
#or
somearray << anotherarray # => ["some", "thing", ["another", "thing"]]
somearray.flatten! # => ["some", "thing", "another", "thing"]
somearray # => ["some", "thing", "another", "thing"]
ri Array@flatten!
Why this question is getting so many votes? The doc is explicitArray#flatten!
Flattens self in place. Returns nil if no modifications were made (i.e., the array contains no subarrays.) – yeyoflatten!
doesn't work like that. Finally, the question reflects a logic problem rather than an optimization problem. See pilcrow's answer below for more. – yeyo