Consider the following input:
input = [:a, :b, :c]
# output = input.join_array(:x)
What is a readable and concise way to get the following output (in Ruby):
[:a, :x, :b, :x, :c]
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possible duplicate of How to insert a new element in between all elements of a Ruby array?tokland– tokland2013-10-30 15:06:46 +00:00Commented Oct 30, 2013 at 15:06
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2the name of the abstraction is "intersperse", you'll find some existing questions by that name.tokland– tokland2013-10-30 15:07:34 +00:00Commented Oct 30, 2013 at 15:07
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Thanks, the name "intersperse" is exactly what I was looking for!jnorris– jnorris2013-10-30 15:09:25 +00:00Commented Oct 30, 2013 at 15:09
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5 Answers
A naive approach:
input = [:a, :b, :c]
input.flat_map{|elem| [elem, :x]}[0...-1] # => [:a, :x, :b, :x, :c]
Without cutting last element:
res = input.reduce([]) do |memo, elem|
memo << :x unless memo.empty?
memo << elem
end
res # => [:a, :x, :b, :x, :c]
answered Oct 30, 2013 at 14:49
Sergio Tulentsev
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4 Comments
Beat Richartz
Upvoted, I think
.flat_map{|elem| [elem, :x]}[0...-1] would be a little bit more readable though.
Sergio Tulentsev
You can't use
[0..-1], it'll include trailing :x.Beat Richartz
Notice the third dot
... which makes the range exclusiveSergio Tulentsev
@BeatRichartz: ah! So you see, for some people it's just more confusing :)
Flatten a Product
You can use Array#product to distribute :x throughout your array, and then flatten the result. For example:
input = [:a, :b, :c]
input.product([:x]).flatten
#=> [:a, :x, :b, :x, :c, :x]
Trimming an Array
Assuming your desired result wasn't just a typo that accidentally excluded the last element, you can use Array#pop, Array#slice, or other similar methods to trim the last element from the array. Some examples include:
input.product([:x]).flatten[0...-1]
#=> [:a, :x, :b, :x, :c]
output = input.product([:x]).flatten
output.pop
output
#=> [:a, :x, :b, :x, :c]
Comments
What about:
input = [:a, :b, :c]
p input.zip([:x].cycle).flatten[0..-2] #=> [:a, :x, :b, :x, :c]
Comments
For fun, we could use join. Not necessarily readable or concise though!
[:a, :b, :c].join('x').chars.map(&:to_sym) # => [:a, :x, :b, :x, :c]
# Or, broken down:
input = [:a, :b, :c]
output = input.join('x') # => "axbxc"
output = output.chars # => ["a", "x", "b", "x", "c"]
output = output.map(&:to_sym) # => [:a, :x, :b, :x, :c]
1 Comment
Sergio Tulentsev
It's not robust. Will break down on longer symbols :)
How is this ?
input = [:a, :b, :c]
p input.each_with_object(:x).to_a.flatten[0..-2]
# >> [:a, :x, :b, :x, :c]
