将“s”添加到数组中每个单词的末尾，除了给定数组中的第二个元素，只使用一行代码

Question

I have an array of single word strings, and I would like to add an 's' to the end of each single word strings except for the 2nd string(element) in the array. I can easily accomplish this using 9 lines of code, but would prefer to do it with 3 lines of code.

Here's my working code using 9 lines.

def add_s(array)
    array.each_with_index.collect do |element, index|
        if index == 1
            element
        else element[element.length] = "s"
            element
        end
    end
end

Here's my broken code while only trying to use 3 lines.

def add_s(array)
    array.each_with_index.map {|element, index| index == 1 ? element : element[element.length] = "s"}
end

Above will return...

array = ["hand", "feet", "knee", "table"]
add_s(array) => ["s", "feet", "s", "s"]

I'm trying to get...

array = ["hand", "feet", "knee", "table"]
add_s(array) => ["hands", "feet", "knees", "tables"]

Answer 1

You should clearly distinguish methods mutating the receiver (the variable they are called on) vs pure methods having no side effects. Also, you should care about what the method returns if you are to use the result of the method.

Here the method for all indices (but 1 ) returns "s" because it is what the block returns:

foo = "bar"
foo[foo.length] = "s"
#⇒ "s"

If you'll check your mutated array afterward, you'll see it was successfully modified to what you wanted.

input = %w[hand feet knee table]
def add_s(input)
  input.each_with_index.map do |element, index|
    index == 1 ? element : element[element.length] = "s"
  end
  input # ⇐ HERE :: return the mutated object
end
#⇒ ["hands", "feet", "knees", "tables"]

or even easier, do not map , just iterate and mutate:

input = %w[hand feet knee table]
def add_s(input)
  input.each_with_index do |element, index|
    element[element.length] = "s" unless index == 1
  end
end

---

Instead of mutating the array inplace, the preferred solution would be to return a modified version. For that you should return new values from a block:

def add_s(input)
  input.each_with_index.map do |element, index|
    index == 1 ? element : element + "s"
  end
end
#⇒ ["hands", "feet", "knees", "tables"]

---

If I were given such a task, I would maintain a list of elements to be skipped as well since sooner or later there will be more than one:

input = %w[hand feet knee scissors table]
to_skip = [1, 3]
def add_s(input)
  input.each_with_index.map do |element, index|
    next element if to_skip.include?(index)
    element + "s"
  end
end
#⇒ ["hands", "feet", "knees", "scissors", "tables"]

Answer 2

["hand", "feet", "knee", "table"].map.with_index{|v,i| i==1 ? v : v + 's'}
#=> ["hands", "feet", "knees", "tables"]

map.with_index helps.
Basically map.with_index equals to each_with_index.collect .
each with collect (same as map ) is superfluous.

If you want to mutate original array, you can change + to << , but not recommended.

Answer 3

I suggest following to achieve as per provided words,

arr = ['apple', 'knee', 'crab', 'jails']
arr.each_with_index.map { |x,i| i == 1  ? x : x + 's' }
=> ["apples", "knee", "crabs", "jailss"]

but to avoid unwanted extra 's' at the end of the strings,

arr = ['apple', 'knee', 'crab', 'jails']
arr.each_with_index.map { |x,i| i == 1 || x[-1] == 's' ? x : x + 's' }
=> ["apples", "knee", "crabs", "jails"]

Answer 4

Linebreaks in Ruby are completely optional, they can always be replaced by a keyword, a semicolon, or sometimes removed altogether. Therefore, it is always trivially possible to write any Ruby program, no matter how complex, in one line.

Here's your code in one line:

def add_s(array) array.each_with_index.collect do |element, index| if index == 1 then element else element[element.length] = "s"; element end end end

However, I am not entirely sure why you want that code on one line, because your original version is much more readable.

Answer 5

It's easy to achieve this using 'active_support'

arr = ["hand", "feet", "knee", "table"]

2.0.0-p648 :023 > require 'active_support/inflector'
 => true

arr.map { |a| arr.index(a) == 1 ? a : a.pluralize }
 => ["hands", "feet", "knees", "tables"]