Convert a string based on hash values [closed] - ruby

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I am trying to write a method that takes in a string and a hash and "encodes" the string based on hash keys and values.
def encode(str,encoding)
end
str = "12#3"
encoding = {"1" => "one", "2"=> "two", "3"=> "three"}
I am expecting the output to be "one two three" any char in the string that is not a key in the hash is replaced with an empty string.
Right now my code looks like the following:
def encode(str, encoding)
output = ""
str.each_char do |ch|
if encoding.has_key?(ch)
output += encoding[ch]
else
output += ""
end
end
return output
end
Any help is appreciated

Answer 1

You can use use the form of String#gsub that uses a hash for substitutions, and a simple regex:
str = "12#3"
encoding = {"1"=>"one", "2"=>"two", "3"=>"three"}
First create a new hash that adds a space to each value in encoding:
adj_encoding = encoding.each_with_object({}) { |(k,v),h| h[k] = "#{v} " }
#=> {"1"=>"one ", "2"=>"two ", "3"=>"three "}
Now perform the substitutions and strip off the extra space if one of the keys of encoding is the last character of str:
str.gsub(/./, adj_encoding).rstrip
#=> "one two three"
Another example:
"1ab 2xx4cat".gsub(/./, adj_encoding).rstrip
#=> "one two"
Ruby determines whether each character of str (the /./ part) equals a key of adj_encodeing. If it does, she substitutes the key's value for the character; else she substitutes an empty string ('') for the character.

Answer 2

You can build a regular expression that matches your keys via Regexp.union:
re = Regexp.union(encoding.keys)
#=> /1|2|3/
scan the string for occurrences of keys using that regular expression:
keys = str.scan(re)
#=> ["1", "2", "3"]
fetch the corresponding values using values_at:
values = encoding.values_at(*keys)
#=> ["one", "two", "three"]
and join the array with a single space:
values.join(' ')
#=> "one two three"
As a "one-liner":
encoding.values_at(*str.scan(Regexp.union(encoding.keys))).join(' ')
#=> "one two three"

Answer 3

Try:
def encode(str, encoding)
output = ""
str.each_char do |ch|
if encoding.has_key?(ch)
output += encoding[ch] + " "
else
output += ""
end
end
return output.split.join(' ')
end
str = "12#3"
encoding = {"1" => "one", "2"=> "two", "3"=> "three"}
p encode(str, encoding) #=> "one two three"

Answer 4

If you are expecting "one two three" you just need to add an space to your concat line and before return, add .lstrip to remove the first space.
Hint: You don't need the "else" concatenating an empty string. If the "#" don't match the encoding hash, it will be ignored.
Like this:
#str = "12#3"
#encoding = {"1" => "one", "2"=> "two", "3"=> "three"}
def encode(str, encoding)
output = ""
str.each_char do |ch|
if encoding.has_key?(ch)
output += " " + encoding[ch]
end
end
return output.lstrip
end
# Output: "one two three"

Answer 5

I would do:
encoding = {"1" => "one", "2"=> "two", "3"=> "three"}
str = "12#3"
str.chars.map{|x|encoding.fetch(x,nil)}.compact.join(' ')
Or two lines like this:
in_encoding_hash = -> x { encoding.has_key? x }
str.chars.grep(in_encoding_hash){|x|encoding[x]}.join(' ')