Ruby method conditions - ruby

Question

The instructions for my program are to make a method that takes a string and returns dashes around any odd numbers, but with the exception that the end result may not begin or end with a dash "-". For example, if I enter "95601137", it should return
"9 - 5 - 6 0 - 1 - 1 - 3 - 7"
Here's the code:
def dashes(number)
string = number.to_s
i=0
final = []
while i<string.length
digit = string[i].to_i
if ((digit)%2 != 0) && (i==0) && (string.length == 1) && ((string.length - 1) == 0)
final.push(string[i])
elsif ((digit)%2 != 0) && (i==0) && (string.length != 1) && ((string.length - 1) > 0)
final.push(string[i] + "-")
elsif ((digit)%2 != 0) && (i>0) && (i!=(string.length - 1)) && ((string.length != 1))
final.push("-" + string[i] + "-")
elsif ((digit)%2 != 0) && (i!=0) && (i==(string.length - 1))
final.push("-" + string[i])
else final.push(string[i])
end
i+=1
end
return final
end
puts("Give me any number.")
answer = gets
puts dashes(answer)
My program has two issues:
When I enter 9, it returns "9-". How come?
When I enter a string that ends with an odd number, it puts a dash at the end, which it's not expected. I thought I made my if conditions strict, too.

Answer 1

I'd like to propose another solution:
def dashes(num)
str = num.to_s
dashed_arr = str.chars.map.with_index do |digit, index|
next digit if digit.to_i.even?
if index.zero? # is it first digit?
"#{digit} -"
elsif index == str.length - 1 # is it last digit?
"- #{digit}"
else
"- #{digit} -"
end
end
dashed_arr.join(' ').gsub('- -', '-')
end
puts dashes(95601137)
puts dashes(909)
# => "9 - 5 - 6 0 - 1 - 1 - 3 - 7"
# => "9 - 0 - 9"
Let's review it step by step:
str = num.to_s - convert our number to a string representation, i.e. "95601137"
str.chars - split our string by chars. We get an array of chars, like this: ["9", "5", "6", "0", "1", "1", "3", "7"], because we want to iterate them, one by one.
map takes one array and converts it to another array by the code supplied in do ... end.
For example, let's take this code:
[1, 2, 3].map do |num|
num * 2
end
# => [2, 4, 6]
If you need also an index of your element, you can similarly use .map.with_index (index starts from zero):
[1, 2, 3].map.with_index do |num, index|
num * index # index takes values 0, 1, 2
end
# => [0, 2, 6]
So, in the block in code above, we have each digit from our number as digit and its 0-based position as index.
next digit if digit.to_i.even?. We don't need even digits, so we can skip them. .to_i is needed to convert digit to integer, so we can query is it even or odd. next digit just returns current digit and moves execution to next digit.
Now we're left only with odd digits, so we just need to put dashes correctly, depending on the digit position: if it's a first digit, append a dash, if it's a last digit then put the dash in front of the digit, otherwise just surround digit with dashes:
if index.zero? # first digit, index is zero-based
"#{digit} -"
elsif index == str.length - 1 # last digit
"- #{digit}"
else
"- #{digit} -"
end
We save intermediate result in dashed_arr variable to make code readable. Right now it contains the following: ["9 -", "- 5 -", "6", "0", "- 1 -", "- 1 -", "- 3 -", "- 7"]. As you can see, we're almost done, we just need to connect all the elements of array back to string.
dashed_arr.join(' '). Join back elements of array into a string with single space as a separator. We get this string: 9 - - 5 - 6 0 - 1 - - 1 - - 3 - - 7. Hmm, it seems we need to delete some consecutive dashes.
Let's do it with gsub: dashed_arr.join(' ').gsub('- -', '-'). gsub just searches all occurrences of first string and replaces them with the second string, which is exactly what we need: 9 - 5 - 6 0 - 1 - 1 - 3 - 7.
We're done! I hope it was also fun for you as for me.

Answer 2

One more implementation, inspired by Cary Swoveland's first implementation:
str = '95601137'
separators = str.each_char.map(&:to_i).each_cons(2).map do |pair|
pair.any?(&:odd?) ? ' - ' : ' '
end
str.chars.zip(separators).join
# => "9 - 5 - 6 0 - 1 - 1 - 3 - 7"

Answer 3

Here are two ways, for:
str = "95601137"
Use an enumerator
With this method you would use String#each_char to create an enumerator to which you would send the methods Enumerator#next and Enumerator#peek:
enum = str.each_char
s = ''
loop do
c = enum.next
s << c
n = enum.peek
s << ((c.to_i.odd? || n.to_i.odd?) ? ' - ' : ' ')
end
s #=> "9 - 5 - 6 0 - 1 - 1 - 3 - 7"
The key here is that when the enumerator is at the last element ('7') peek raises a StopIteration exception. The exception is handled by Kernel#loop by breaking out of the loop.
Use String#gsub
We can use gsub three times, each with a regular expression, to:
put the dashes in the correct locations
space as desired around the dashes
space as desired between even digits
r = /
(\A\d) # match beginning of string followed by a digit, save in group 1
| # or
(\d\z) # match a digit followed by end of string, save in group 2
| # or
(\d) # match a digit, save in capture group 3
/x # extended mode
str = "95601137"
str.gsub(r) do |s|
if $1
$1.to_i.odd? ? "#{$1}-" : $1
elsif $2
$2.to_i.odd? ? "-#{$2}" : $2
elsif $3
$3.to_i.odd? ? "-#{$3}-" : $3
else
raise ArgumentError, "'#{s}' is not a digit"
end
end.gsub(/-+/, ' - ').gsub(/(\d)(\d)/,'\1 \2')
#=> "9 - 5 - 6 0 - 1 - 1 - 3 - 7"

Answer 4

Replace:
answer = gets
with:
answer = gets.strip
Then, you will get the correct output for input: 9
Because, when you give 9 as input and hit enter, your input is actually: "9\n" which has length 2. That's why it was printing 9-.
Using: gets.strip you just strip out the \n.
To remove the last - (if any), you can use chomp:
final_result = final.join('').chomp('-')
And, to remove the first - (if any), you can use this logic:
if final_result[0] == '-'
final_result[1..-1]
else
final_result
end
Here is the full working version of the code (keeping as much as of your code):
def dashes(number)
string = number.to_s
i = 0
final = []
while i < string.length
digit = string[i].to_i
if ((digit)%2 != 0) && (i==0) && (string.length == 1) && ((string.length - 1) == 0)
final.push(string[i])
elsif ((digit)%2 != 0) && (i==0) && (string.length != 1) && ((string.length - 1) > 0)
final.push(string[i] + "-")
elsif ((digit)%2 != 0) && (i>0) && (i!=(string.length - 1)) && ((string.length != 1))
final.push("-" + string[i] + "-")
elsif ((digit)%2 != 0) && (i!=0) && (i==(string.length - 1))
final.push("-" + string[i])
else
final.push(string[i])
end
i += 1
end
final_result = final.join('').gsub('--', '-').chomp('-')
puts "final_result: #{final_result.inspect}"
if final_result[0] == '-'
final_result[1..-1]
else
final_result
end
end
puts("Give me any number.")
answer = gets.strip
puts dashes(answer)
# > Give me any number.
# > 95601137
# > "9-5-60-1-1-3-7"

Answer 5

A naive implementation, there's probably some smarter ways to do it:
def dashes(number)
number # => 95601137
.to_s # => "95601137"
.chars # => ["9", "5", "6", "0", "1", "1", "3", "7"]
.map(&:to_i) # => [9, 5, 6, 0, 1, 1, 3, 7]
.map {|i| i.odd? ? "-#{i}-" : i } # => ["-9-", "-5-", 6, 0, "-1-", "-1-", "-3-", "-7-"]
.join # => "-9--5-60-1--1--3--7-"
.gsub(/^-|-$/, '') # => "9--5-60-1--1--3--7"
.gsub('--', '-') # => "9-5-60-1-1-3-7"
end