How can I join an array with from and to?

Question

I have an array, I would like to concat all values except the first one element.

For example: Doing it on the array [1,2,3,4,5] should output 2345

I tried to do it with row.join("") but I could not figure out how to do it.

Answer 1

Your question almost certainly just suffers from poor formatting, but if you actually want a number back rather than a string, you could do something like:

irb(main):018:0> a = [1, 2, 3, 4, 5]
irb(main):019:0> num = 0
irb(main):020:0> a.drop(1).reverse.each_with_index { |digit, i| num += digit * 10 ** i }
=> [5, 4, 3, 2]
irb(main):021:0> num
=> 2345

Or perhaps:

irb(main):033:0> a = [1, 2, 3, 4, 5]
irb(main):034:0> a.drop(1).reverse.each_with_index.reduce(0) { |acc, (x, i)| acc + x * 10 ** i }
=> 2345

Answer 2

Here's another approach using the * or "splat" operator and multiple_assignments:

dropped, *kept =  [1,2,3,4,5]
kept.join
#=>  "2345"

The splat can be used to deconstruct the array in a plethora of other ways as well such as:

drop, drop, *keep =  [1,2,3,4,5]
keep  #=>  [3, 4, 5]

*keep, drop =  [1,2,3,4,5]
keep  #=>  [1, 2, 3, 4]

first,*middle, last =  [1,2,3,4,5]
first #=>  1
middle  #=>  [2, 3, 4]
last  #=>  5

...just to name a few

Answer 3

You can use:

yourList = [1,2,3,4,5]
yourList.shift
puts "#{yourList.join("")}\n\n"

OUTPUT: 2345