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Task I want to solve:
Write a program that takes a string, will perform a transformation and return it.
For each of the letters of the parameter string switch it by the next one in alphabetical order.
'z' becomes 'a' and 'Z' becomes 'A'. Case remains unaffected.
def rotone(param_1)
a = ""
param_1.each_char do |x|
if x.count("a-zA-Z") > 0
a << x.succ
else
a << x
end
end
a
end
And I take this:
Input: "AkjhZ zLKIJz , 23y "
Expected Return Value: "BlkiA aMLJKa , 23z "
Return Value: "BlkiAA aaMLJKaa , 23z "
When iterators find 'z' or 'Z' it increment two times z -> aa or Z -> AA
input = "AkjhZ zLKIJz , 23y"
Code
p input.tr('a-yA-YzZ','b-zB-ZaA')
Output
"BlkiA aMLJKa , 23z"
Your problem is that String#succ (aka String#next) has been designed in a way that does not serve your purpose when the receiver is 'z' or 'Z':
'z'.succ #=> 'aa'
'Z'.succ #=> 'AA'
If you replaced a << x.succ with a << x.succ[0] you would obtain the desired result.
You might consider writing that as follows.
def rotone(param_1)
param_1.gsub(/./m) { |c| c.match?(/[a-z]/i) ? c.succ[0] : c }
end
String#gsub's argument is a regular expression that matches every character (so every character is passed to gsub's block)1.
See also String#match?. The regular expression /[a-z]/i matches every character that is one of the characters in the character class [a-z]. The option i makes the match case-independent, so uppercase letters are matched as well.
Here is alternative way to write the method that employs two hashes that are defined as constants.
CODE = [*'a'..'z', *'A'..'Z'].each_with_object({}) do |c,h|
h[c] = c.succ[0]
end.tap { |h| h.default_proc = proc { |_h,k| k } }
#=> {"a"=>"b", "b"=>"c",..., "y"=>"z", "z"=>"a",
# "A"=>"B", "B"=>"C",..., "Y"=>"Z", "Z"=>"A"}
DECODE = CODE.invert.tap { |h| h.default_proc = proc { |_h,k| k } }
#=> {"b"=>"a", "c"=>"b", ..., "z"=>"y", "a"=>"z",
# "B"=>"A", "C"=>"B", ..., "Z"=>"Y", "A"=>"Z"}
For example,
CODE['e'] #=> "f"
CODE['Z'] #=> "A"
CODE['?'] #=> "?"
DECODE['f'] #=> "e"
DECODE['A'] #=> "Z"
DECODE['?'] #=> "?"
Let's try using gsub, CODE and DECODE with an example string.
str = "The quick brown dog Zelda jumped over the lazy fox Arnie"
rts = str.gsub(/./m, CODE)
#=> "Uif rvjdl cspxo eph Afmeb kvnqfe pwfs uif mbaz gpy Bsojf"
rts.gsub(/./m, DECODE)
#=> "The quick brown dog Zelda jumped over the lazy fox Arnie"
See Hash#merge, Object#tap, Hash#default_proc=, Hash#invert and the form of Sting#gsub that takes a hash as its optional second argument.
Adding the default proc to the hash h causes h[k] to return k if h does not have a key k. Had CODE been defined without the default proc,
CODE = [*'a'..'z', *'A'..'Z'].each_with_object({}) { |c,h| h[c] = c.succ[0] }
#=> {"a"=>"b", "b"=>"c",..., "y"=>"z", "z"=>"a",
# "A"=>"B", "B"=>"C",..., "Y"=>"Z", "Z"=>"A"}
gsub would skip over characters that are not letters:
rts = str.gsub(/./m, CODE)
#=> "UifrvjdlcspxoephAfmebkvnqfepwfsuifmbazgpyBsojf"
Without the default proc we would have to write
rts = str.gsub(/./m) { |s| CODE.fetch(s, s) }
#=> "Uif rvjdl cspxo eph Afmeb kvnqfe pwfs uif mbaz gpy Bsojf"
See Hash#fetch.
1. The regular expression /./ matches every character other than line terminators. Adding the option m (/./m) causes . to match line terminators as well.
I've been attempting a coding exercise to mask all but the last four digits or characters of any input.
I think my solution works but it seems a bit clumsy. Does anyone have ideas about how to refactor it?
Here's my code:
def mask(string)
z = string.to_s.length
if z <= 4
return string
elsif z > 4
array = []
string1 = string.to_s.chars
string1[0..((z-1)-4)].each do |s|
array << "#"
end
array << string1[(z-4)..(z-1)]
puts array.join(", ").delete(", ").inspect
end
end
positive lookahead
A positive lookahead makes it pretty easy. If any character is followed by at least 4 characters, it gets replaced :
"654321".gsub(/.(?=.{4})/,'#')
# "##4321"
Here's a description of the regex :
r = /
. # Just one character
(?= # which must be followed by
.{4} # 4 characters
) #
/x # free-spacing mode, allows comments inside regex
Note that the regex only matches one character at a time, even though it needs to check up to 5 characters for each match :
"654321".scan(r)
# => ["6", "5"]
/(.)..../ wouldn't work, because it would consume 5 characters for each iteration :
"654321".scan(/(.)..../)
# => [["6"]]
"abcdefghij".scan(/(.)..../)
# => [["a"], ["f"]]
If you want to parametrize the length of the unmasked string, you can use variable interpolation :
all_but = 4
/.(?=.{#{all_but}})/
# => /.(?=.{4})/
Code
Packing it into a method, it becomes :
def mask(string, all_but = 4, char = '#')
string.gsub(/.(?=.{#{all_but}})/, char)
end
p mask('testabcdef')
# '######cdef'
p mask('1234')
# '1234'
p mask('123')
# '123'
p mask('x')
# 'x'
You could also adapt it for sentences :
def mask(string, all_but = 4, char = '#')
string.gsub(/\w(?=\w{#{all_but}})/, char)
end
p mask('It even works for multiple words')
# "It even #orks for ####iple #ords"
Some notes about your code
string.to_s
Naming things is very important in programming, especially in dynamic languages.
string.to_s
If string is indeed a string, there shouldn't be any reason to call to_s.
If string isn't a string, you should indeed call to_s before gsub but should also rename string to a better description :
object.to_s
array.to_s
whatever.to_s
join
puts array.join(", ").delete(", ").inspect
What do you want to do exactly? You could probably just use join :
[1,2,[3,4]].join(", ").delete(", ")
# "1234"
[1,2,[3,4]].join
# "1234"
delete
Note that .delete(", ") deletes every comma and every whitespace, in any order. It doesn't only delete ", " substrings :
",a b,,, cc".delete(', ')
# "abcc"
["1,2", "3,4"].join(', ').delete(', ')
# "1234"
Ruby makes this sort of thing pretty trivial:
class String
def asteriskify(tail = 4, char = '#')
if (length <= tail)
self
else
char * (length - tail) + self[-tail, tail]
end
end
end
Then you can apply it like this:
"moo".asteriskify
# => "moo"
"testing".asteriskify
# => "###ting"
"password".asteriskify(5, '*')
# => "***sword"
Try this one
def mask(string)
string[0..-5] = '#' * (string.length - 4)
string
end
mask("12345678")
=> "####5678"
I will add my solution to this topic too :)
def mask(str)
str.match(/(.*)(.{4})/)
'#' * ($1 || '').size + ($2 || str)
end
mask('abcdef') # => "##cdef"
mask('x') # => "x"
I offer this solution mainly to remind readers that String#gsub without a block returns an enumerator.
def mask(str, nbr_unmasked, mask_char)
str.gsub(/./).with_index { |s,i| i < str.size-nbr_unmasked ? mask_char : s }
end
mask("abcdef", 4, '#')
#=> "##cdef"
mask("abcdef", 99, '#')
#=> "######"
Try using tap
def mask_string(str)
str.tap { |p| p[0...-4] = '#' * (p[0...-4].length) } if str.length > 4
str
end
mask_string('ABCDEF') # => ##CDEF
mask_string('AA') # => AA
mask_string('S') # => 'S'
Here is my code in ruby for a word compression.
For any given word (e.g. abbbcca) the compressed word/output should be in the format as "letter+repetition" (for above example, output: a1b3c2a1).
Here I'm so close to the completion but my result isn't in the expected format. It's counting the whole letters in string.chars.each thus resulting output as a2b3c2a2.
Any help?
def string_compressor(string)
new_string = []
puts string.squeeze
string.squeeze.chars.each { |s|
count = 0
string.chars.each { |w|
if [s] == [w]
count += 1
end
}
new_string << "#{s}#{count}"
puts "#{new_string}"
}
if new_string.length > string.length
return string
elsif new_string.length < string.length
return new_string
else "Equal"
end
end
string_compressor("abbbcca")
'abbbcca'.chars.chunk{|c| c}.map{|c, a| [c, a.size]}.flatten.join
Adapted from a similar question.
Similar:
'abbbcca'.chars.chunk{|c| c}.map{|c, a| "#{c}#{a.size}"}.join
See chunk documentation
You can use a regular expression for that.
'abbbcca'.gsub(/(.)\1*/) { |m| "%s%d" % [m[0], m.size] }
#=> "a1b3c2a1"
The regular expression reads, "match any character, capturing it in group 1. Then match the contents of capture group 1 zero or more times".
As you said, your code counts every letter in the string, not just the one grouped next to one another.
Here's a modified version :
def display_count(count)
if count == 1
""
else
count.to_s
end
end
def string_compressor(string)
new_string = ''
last_char = nil
count = 0
string.chars.each do |char|
if char == last_char
count += 1
else
new_string << "#{last_char}#{display_count(count)}" if last_char
last_char = char
count = 1
end
end
new_string << "#{last_char}#{display_count(count)}" if last_char
new_string
end
p string_compressor('abbbcca') #=> "ab3c2a"
p string_compressor('aaaabbb') #=> "a4b3"
p string_compressor('aabb') #=> "a2b2"
p string_compressor('abc') #=> "abc"
Note that with display_count removing 1s from the string, new_string can never be longer than string. It also probably isn't a good idea to return Equal as a supposedly compressed string.
To decompress the string :
def string_decompressor(string)
string.gsub(/([a-z])(\d+)/i){$1*$2.to_i}
end
p string_decompressor("a5b11") #=> "aaaaabbbbbbbbbbb"
p string_decompressor("ab3c2a") #=> "abbbcca"
I have a Caesar Cipher script in Ruby that is working but it returns the string as all upper-case letters instead of preserving the cases of the original string.
I could use capitalize to make it look good enough but I would like a more concrete way of preserving the cases.
Here is the script:
BASE_ORD = 'A'.ord
def caesar_cipher(phrase, key)
cipher = phrase.gsub(/[a-z]/i) do |c|
orig_pos = c.upcase.ord - BASE_ORD
new_pos = (orig_pos + key) % 26
(new_pos + BASE_ORD).chr
end
puts cipher
end
caesar_cipher("What a string!", 5)
Any help or insight would be appreciated.
The simplest solution, given your existing code, is to check whether the character is uppercase or lowercase and set base_ord accordingly. Since the lowercase letters come after the uppercase letters in UTF-8 (as in ASCII), we can just test letter >= 'a', e.g.:
base_ord = (letter >= 'a' ? 'a' : 'A').ord
Here's the whole method with this change (you no longer need the BASE_ORD constant):
def caesar_cipher(phrase, key)
phrase.gsub(/[a-z]/i) do |letter|
base_ord = (letter >= 'a' ? 'a' : 'A').ord
orig_pos = letter.ord - base_ord
new_pos = (orig_pos + key) % 26
(new_pos + base_ord).chr
end
end
puts caesar_cipher("What a string!", 5) # => Bmfy f xywnsl!
Edit
Amadan makes a good point about using String#tr. Here's a somewhat more concise implementation:
ALPHABET = "aAbBcCdDeEfFgGhHiIjJkKlLmMnNoOpPqQrRsStTuUvVwWxXyYzZ"
# Or if you want to be fancy: ALPHABET = (?a..?z).flat_map {|c| [ c, c.upcase ] }.join
def caesar_cipher(phrase, key)
to_alphabet = ALPHABET.dup
to_alphabet << to_alphabet.slice!(0, key * 2)
phrase.tr(ALPHABET, to_alphabet)
end
puts caesar_cipher("What a string!", 5) # => Bmfy f xywnsl!
As said in comments, tr is easier to use for Caesar Cypher (once you prepare the two alphabets), and should also be much faster:
class CaesarCypher
def initialize(key, alphabet=nil)
#from_alphabet = alphabet || (?a..?z).to_a.join
#to_alphabet = #from_alphabet[key..-1] + #from_alphabet[0...key]
#from_alphabet += #from_alphabet.upcase
#to_alphabet += #to_alphabet.upcase
end
def encode(str)
str.tr(#from_alphabet, #to_alphabet)
end
def encode!(str)
str.tr!(#from_alphabet, #to_alphabet)
end
def decode(str)
str.tr(#to_alphabet, #from_alphabet)
end
def decode(str)
str.tr!(#to_alphabet, #from_alphabet)
end
end
cc = CaesarCypher.new(1)
puts cc.encode("Caesar, huh?")
puts cc.decode("Dbftbs, ivi?")
I am trying to change numbers up to 100 from integers into words, but have run into some trouble, can anyone point out what is missing with my code:
def in_words(integer)
numWords = {
0=>"zero",
1=>"one",
2=>"two",
3=>"three",
4=>"four",
5=>"five",
6=>"six",
7=>"seven",
8=>"eight",
9=>"nine",
10=>"ten",
11=>"eleven",
12=>"twelve",
13=>"thirteen",
14=>"fourteen",
15=>"fifteen",
16=>"sixteen",
17=>"seventeen",
18=>"eighteen",
19=>"nineteen",
20=>"twenty",
30=>"thirty",
40=>"fourty",
50=>"fifty",
60=>"sixty",
70=>"seventy",
80=>"eighty",
90=>"ninety",
100=>"one hundred"
}
array = integer.to_s.split('')
new_array = []
numWords.each do |k,v|
array.each do |x|
if x = k
new_array.push(v)
end
end
end
new_array.join('')
end
Right now when I do:
inwords(0)
I get the following:
=>"zeroonetwothreefourfivesixseveneightnineteneleventwelvethirteenfourteenfiftee nsixteenseventeeneighteennineteentwentythirtyfourtyfiftysixtyseventyeightyninetyone hundred"
Edit
I noticed your code iterates through the array a lot of times and uses the = instead of the == in your if statements.
Your code could be more efficient using the Hash's #[] method in combination with the #map method.., here's a one-line alternative:
integer.to_s.split('').map {|i| numWords[i.to_i]} .join ' '
Also, notice that the integer.to_s.split('') will split the array into one-digit strings, so having numbers up to a hundred isn't relevant for the code I proposed.
To use all the numbers in the Hash, you might want to use a Regexp to identify the numbers you have. One way is to do the following (I write it in one line, but it's easy to break it down using variable names for each step):
integer.to_s.gsub(/(\d0)|([1]?\d)/) {|v| v + " "} .split.map {|i| numWords[i.to_i]} .join ' '
# or:
integer.to_s.gsub(/(#{numWords.keys.reverse.join('|')})/) {|v| v + " "} .split.map {|i| numWords[i.to_i]} .join ' '
# out = integer.to_s
# out = out.gsub(/(#{numWords.keys.reverse.join('|')})/) {|v| v + " "}
# out = out.split
# out = out.map {|i| numWords[i.to_i]}
# out = out.join ' '
Edit 2
Since you now mention that you want the method to accept numbers up to a hundred and return the actual number (23 => twenty three), maybe a different approach should be taken... I would recommend that you update your question as well.
def in_words(integer)
numWords = {
0=>"zero",
1=>"one",
2=>"two",
3=>"three",
4=>"four",
5=>"five",
6=>"six",
7=>"seven",
8=>"eight",
9=>"nine",
10=>"ten",
11=>"eleven",
12=>"twelve",
13=>"thirteen",
14=>"fourteen",
15=>"fifteen",
16=>"sixteen",
17=>"seventeen",
18=>"eighteen",
19=>"nineteen",
20=>"twenty",
30=>"thirty",
40=>"fourty",
50=>"fifty",
60=>"sixty",
70=>"seventy",
80=>"eighty",
90=>"ninety",
100=>"one hundred"
}
raise "cannot accept such large numbers" if integer > 100
raise "cannot accept such small numbers" if integer < 0
return "one hundred" if integer == 100
if integer < 20 || integer %10 == 0
numWords[integer]
else
[numWords[integer / 10 * 10], numWords[integer % 10]].join ' '
end
end
the integer / 10 * 10 makes the number a round number (ten, twenty, etc') because integers don't have fractions (so, 23/10 == 2 and 2 * 10 == 20). The same could be achieved using integer.round(-1), which is probably better.
It seems like all you're trying to do is find a mapping from an implicit hash
module NumWords
INT2STR = {
0=>"zero",
1=>"one",
2=>"two",
3=>"three",
4=>"four",
5=>"five",
6=>"six",
7=>"seven",
8=>"eight",
9=>"nine",
10=>"ten",
11=>"eleven",
12=>"twelve",
13=>"thirteen",
14=>"fourteen",
15=>"fifteen",
16=>"sixteen",
17=>"seventeen",
18=>"eighteen",
19=>"nineteen",
20=>"twenty",
30=>"thirty",
40=>"fourty",
50=>"fifty",
60=>"sixty",
70=>"seventy",
80=>"eighty",
90=>"ninety",
100=>"one hundred"
}
module_function
def in_words(integer)
INT2STR[integer]
end
end
The above code separates the hash definition from the method call so that the hash doesn't get recreated every time you call in_words.
You can also use Hash#fetch instead of Hash#[] as Andrey pointed out.
Your test whether x = k is your first problem (in two ways).
Firstly, if x = k means assign the value of k to x and then execute the if block if that value is true (basically anything other than false or nil).
What you should actually be testing is x == k which will return true if x is equal to k.
The second problem is that you converted your number into an array of string representation so you are comparing, for example, if "0" == 0. This won't return true because they are different types.
If you convert it to if x.to_i == k then your if block will be executed and you'll get:
> in_words(0)
=> "zero"
Then you get to move onto the next problem which is that you're looking at your number digit by digit and some of the values you are testing against need two digits to be recognised:
> in_words(10)
=> "zeroone"
You might be in looking at a different question then - or maybe that is the question you wanted answered all along!
Here's another way you might do it:
ONES_TO_TEXT = { 0=>"zero", 1=>"one", 2=>"two", 3=>"three", 4=>"four",
5=>"five", 6=>"six", 7=>"seven", 8=>"eight", 9=>"nine" }
TEENS_TO_TEXT = { 10=>"ten", 11=>"eleven", 12=>"twelve",
13=>"thirteen", 15=>"fifteen" }
TENS_TO_TEXT = { 2=>"twenty", 3=>"thirty", 5=>"fifty", 8=>"eighty" }
def in_words(n)
raise ArgumentError, "#{n} is out-of_range" unless (0..100).cover?(n)
case n.to_s.size
when 1 then ONES_TO_TEXT[n]
when 3 then "one hundred"
else
case n
when (10..19)
TEENS_TO_TEXT.key?(n) ? TEENS_TO_TEXT[n] : ONES_TO_TEXT[n]+"teen"
else
t,o = n.divmod(10)
(TENS_TO_TEXT.key?(t) ? TENS_TO_TEXT[t] : ONES_TO_TEXT[t]+"ty") +
(o.zero? ? '' : "-#{ONES_TO_TEXT[o]}")
end
end
end
Let's try it:
in_words(5) #=> "five"
in_words(10) #=> "ten"
in_words(15) #=> "fifteen"
in_words(20) #=> "twenty"
in_words(22) #=> "twenty-two"
in_words(30) #=> "thirty"
in_words(40) #=> "fourty"
in_words(45) #=> "fourty-five"
in_words(50) #=> "fifty"
in_words(80) #=> "eighty"
in_words(99) #=> "ninety-nine"
in_words(100) #=> "one hundred"
Here the increased complexity may not be justified, but this approach may in fact simplify the calculations when the maximum permitted value of n is much greater than 100.