How can I check how many times a phrase occurs in a string?
For example, let's say the phrase is donut
str1 = "I love donuts!"
#=> returns 1 because "donuts" is found once.
str2 = "Squirrels do love nuts"
#=> also returns 1 because of 'do' and 'nuts' make up donut
str3 = "donuts do stun me"
#=> returns 2 because 'donuts' and 'do stun' has all elements to make 'donuts'
I checked this SO that suggests using include, but it only works if donuts is spelled in order.
I came up with this, but it doesn't stop spelling after all elements of "donuts"is spelled. i.e. "I love donuts" #=> ["o", "d", "o", "n", "u", "t", "s"]
def word(arr)
acceptable_word = "donuts".chars
arr.chars.select { |name| acceptable_word.include? name.downcase }
end
How can I check how many occurrences of donuts are there in a given string? No edge cases. Input will always be String, no nil. If it contains elements of donut only it should not count as 1 occurrence; it needs to contain donuts, doesn't have to be in order.
Code
def count_em(str, target)
target.chars.uniq.map { |c| str.count(c)/target.count(c) }.min
end
Examples
count_em "I love donuts!", "donuts" #=> 1
count_em "Squirrels do love nuts", "donuts" #=> 1
count_em "donuts do stun me", "donuts" #=> 2
count_em "donuts and nuts sound too delicious", "donuts" #=> 3
count_em "cats have nine lives", "donuts" #=> 0
count_em "feeding force scout", "coffee" #=> 1
count_em "feeding or scout", "coffee" #=> 0
str = ("free mocha".chars*4).shuffle.join
# => "hhrefemcfeaheomeccrmcre eef oa ofrmoaha "
count_em str, "free mocha"
#=> 4
Explanation
For
str = "feeding force scout"
target = "coffee"
a = target.chars
#=> ["c", "o", "f", "f", "e", "e"]
b = a.uniq
#=> ["c", "o", "f", "e"]
c = b.map { |c| str.count(c)/target.count(c) }
#=> [2, 2, 1, 1]
c.min
#=> 1
In calculating c, consider the first element of b passed to the block and assigned to the block variable c.
c = "c"
Then the block calculation is
d = str.count(c)
#=> 2
e = target.count(c)
#=> 1
d/e
#=> 2
This indicates that str contains enough "c"'s to match "coffee" twice.
The remaining calculations to obtain c are similar.
Addendum
If the characters of str matching characters target must be in the same order as those of target, the following regex could be used.
target = "coffee"
r = /#{ target.chars.join(".*?") }/i
#=> /c.*?o.*?f.*?f.*?e.*?e/i
matches = "xcorr fzefe yecaof tfe erg eeffoc".scan(r)
#=> ["corr fzefe ye", "caof tfe e"]
matches.size
#=> 2
"feeding force scout".scan(r).size
#=> 0
The questions marks in the regex are needed to make the searches non-greedy.
The solution is more or less simple (map(&:dup) is used there to avoid inputs mutating):
pattern = 'donuts'
[str1, str2, str3].map(&:dup).map do |s|
loop.with_index do |_, i|
break i unless pattern.chars.all? { |c| s.sub!(c, '') }
end
end
#⇒ [1, 1, 2]
Here's an approach with two variants, one where the letters must appear in order, and one where order is irrelevant. In both cases the frequency of each letter is respected, so "coffee" must match vs. two 'f' and two 'e' letters, "free mocha" is insufficient to match, lacking a second 'f'.
def sorted_string(string)
string.split('').sort.join
end
def phrase_regexp_sequence(phrase)
Regexp.new(
phrase.downcase.split('').join('.*')
)
end
def phrase_regexp_unordered(phrase)
Regexp.new(
phrase.downcase.gsub(/\W/, '').split('').sort.chunk_while(&:==).map do |bit|
"#{bit[0]}{#{bit.length}}"
end.join('.*')
)
end
def contains_unordered(phrase, string)
!!phrase_regexp_unordered(phrase).match(sorted_string(string.downcase))
end
def contains_sequence(phrase, string)
!!phrase_regexp_sequence(phrase).match(string.downcase)
end
strings = [
"I love donuts!",
"Squirrels do love nuts",
"donuts do stun me",
"no stunned matches",
]
phrase = 'donut'
strings.each do |string|
puts '%-30s %s %s' % [
string,
contains_unordered(phrase, string),
contains_sequence(phrase, string)
]
end
# => I love donuts! true true
# => Squirrels do love nuts true true
# => donuts do stun me true true
# => no stunned matches true false
Simple solution:
criteria = "donuts"
str1 = "I love donuts!"
str2 = "Squirrels do love nuts"
str3 = "donuts do stun me"
def strings_construction(criteria, string)
unique_criteria_array = criteria.split("").uniq
my_hash = {}
# Let's count how many times each character of the string matches a character in the string
unique_criteria_array.each do |char|
my_hash[char] ? my_hash[char] = my_hash[char] + 1 : my_hash[char] = string.count(char)
end
my_hash.values.min
end
puts strings_construction(criteria, str1) #=> 1
puts strings_construction(criteria, str2) #=> 1
puts strings_construction(criteria, str3) #=> 2
Related
My code:
def wave(str)
ary = []
increase_num = 0
str = str.chars
until increase_num > str.size
ary << str[increase_num].upcase && increase_num += 1
end
end
What it's supposed to do:
wave("hello") => ["Hello", "hEllo", "heLlo", "helLo", "hellO"]
I would really appreciate some help, as you probably know by looking at it I'm relatively new.
str = "hello"
str.size.times.map { |i| str[0,i] << str[i].upcase << str[i+1..] }
#=> ["Hello", "hEllo", "heLlo", "helLo", "hellO"]
I would go about it as follows:
def wave(str)
str = str.downcase # so we can ensure a wave even if the original string had capitalization
str.each_char.with_index.map do |c,idx|
str[0...idx].concat(c.upcase,str[idx.+(1)..-1])
end
end
wave("hello")
#=> ["Hello", "hEllo", "heLlo", "helLo", "hellO"]
str.each_char.with_index.map do |c,idx| - This converts the String into an Enumerator and yields each character and its index to the map block.
str[0...idx] - In the block we slice the string into characters 0 through index (exclusive)
.concat(c.upcase,str[idx.+(1)..-1]) - Then we concatenate that with the current character upcased and the remaining portion of the String (index + 1 through the end of the String)
First 2 passes will look like:
# idx = 0
# c = "h"
# str[0...idx].concat(c.upcase,str[idx.+(1)..-1])
"".concat("H","ello")
# idx = 1
# c = "e"
# str[0...idx].concat(c.upcase,str[idx.+(1)..-1])
"h".concat("E","llo")
Building out a Rot method to solve encryption. I have something that is working but takes out whitespaces and any characters that are included. Was going to use bytes instead of chars then turn it back into a string once I have the byte code but I can't seem to get it working. How would you go about keeping those in place from this code:
code
def rot(x, string, encrypt=true)
alphabet = Array("A".."Z") + Array("a".."z")
results = []
if encrypt == true
key = Hash[alphabet.zip(alphabet.rotate(x))]
string.chars.each do |i|
if ('a'..'z').include? i
results << key.fetch(i).downcase
elsif ('A'..'Z').include? i
results << key.fetch(i).upcase
end
end
return results.join
else
key_false = Hash[alphabet.zip(alphabet.rotate(26 - x))]
string.chars.each do |i|
if ('a'..'z').include? i
results << key_false.fetch(i).downcase
elsif ('A'..'Z').include? i
results << key_false.fetch(i).upcase
end
end
return results.join
end
end
puts rot(10, "Hello, World")
=> RovvyGybvn
puts rot(10, "Rovvy, Gybvn", false)
=> HelloWorld
Thanks for your help in advance!
Just add to both if blocks an else condition like this:
if ('a'..'z').include? i
# ...
elsif ('A'..'Z').include? i
# ...
else
results << i
end
Which will add all non A-z characters untouched to the output.
I've noticed some issues with your code:
Broken replacement hash
This is the biggest problem - your replacement hash is broken. I'm using a smaller alphabet for demonstration purposes, but this applies to 26 characters as well:
uppercase = Array("A".."C")
lowercase = Array("a".."c")
alphabet = uppercase + lowercase
#=> ["A", "B", "C", "a", "b", "c"]
You build the replacement hash via:
x = 1
key = Hash[alphabet.zip(alphabet.rotate(x))]
#=> {"A"=>"B", "B"=>"C", "C"=>"a", "a"=>"b", "b"=>"c", "c"=>"A"}
"C"=>"a" and "c"=>"A" are referring to the wrong character case. This happens because you rotate the entire alphabet at once:
alphabet #=> ["A", "B", "C", "a", "b", "c"]
alphabet.rotate(x) #=> ["B", "C", "a", "b", "c", "A"]
Instead. you have to rotate the uppercase and lowercase letter separately:
uppercase #=> ["A", "B", "C"]
uppercase.rotate(x) #=> ["B", "C", "A"]
lowercase #=> ["a", "b", "c"]
lowercase.rotate(x) #=> ["B", "C", "A"]
and concatenate the rotated parts afterwards. Either:
key = Hash[uppercase.zip(uppercase.rotate(x)) + lowercase.zip(lowercase.rotate(x))]
#=> {"A"=>"B", "B"=>"C", "C"=>"A", "a"=>"b", "b"=>"c", "c"=>"a"}
or:
key = Hash[(uppercase + lowercase).zip(uppercase.rotate(x) + lowercase.rotate(x))]
#=> {"A"=>"B", "B"=>"C", "C"=>"A", "a"=>"b", "b"=>"c", "c"=>"a"}
Replacing the characters
Back to a full alphabet:
uppercase = Array("A".."Z")
lowercase = Array("a".."z")
x = 10
key = Hash[uppercase.zip(uppercase.rotate(x)) + lowercase.zip(lowercase.rotate(x))]
Having a working replacement hash makes replacing the characters almost trivial:
string = "Hello, World!"
result = ""
string.each_char { |char| result << key.fetch(char, char) }
result
#=> "Rovvy, Gybvn!"
I've changed result from an array to a string. It also has a << method and you don't have to join it afterwards.
Hash#fetch works almost like Hash#[], but you can pass a default value that is returned if the key is not found in the hash:
key.fetch("H", "H") #=> "R" (replacement value)
key.fetch("!", "!") #=> "!" (default value)
Handling encryption / decryption
You're duplicating a lot of code to handle the decryption part. But there's a much easier way - just reverse the direction:
rot(10, "Hello") #=> "Rovvy"
rot(10, "Rovvy", false) #=> "Hello"
rot(-10, "Rovvy") #=> "Hello"
So within your code, you can write:
x = -x unless encrypt
Putting it all together
def rot(x, string, encrypt = true)
uppercase = Array("A".."Z")
lowercase = Array("a".."z")
x = -x unless encrypt
key = Hash[uppercase.zip(uppercase.rotate(x)) + lowercase.zip(lowercase.rotate(x))]
result = ""
string.each_char { |char| result << key.fetch(char, char) }
result
end
rot(10, "Hello, World!") #=> "Rovvy, Gybvn!"
rot(10, "Rovvy, Gybvn!", false) #=> "Hello, World!"
I have this exercise:
Write a Title class which is initialized with a string.
It has one method -- fix -- which should return a title-cased version of the string:
Title.new("a title of a book").fix =
A Title of a Book
You'll need to use conditional logic - if and else statements - to make this work.
Make sure you read the test specification carefully so you understand the conditional logic to be implemented.
Some methods you'll want to use:
String#downcase
String#capitalize
Array#include?
Also, here is the Rspec, I should have included that:
describe "Title" do
describe "fix" do
it "capitalizes the first letter of each word" do
expect( Title.new("the great gatsby").fix ).to eq("The Great Gatsby")
end
it "works for words with mixed cases" do
expect( Title.new("liTTle reD Riding hOOD").fix ).to eq("Little Red Riding Hood")
end
it "downcases articles" do
expect( Title.new("The lord of the rings").fix ).to eq("The Lord of the Rings")
expect( Title.new("The sword And The stone").fix ).to eq("The Sword and the Stone")
expect( Title.new("the portrait of a lady").fix ).to eq("The Portrait of a Lady")
end
it "works for strings with all uppercase characters" do
expect( Title.new("THE SWORD AND THE STONE").fix ).to eq("The Sword and the Stone")
end
end
end
Thank you #simone, I incorporated your suggestions:
class Title
attr_accessor :string
def initialize(string)
#string = string
end
IGNORE = %w(the of a and)
def fix
s = string.split(' ')
s.map do |word|
words = word.downcase
if IGNORE.include?(word)
words
else
words.capitalize
end
end
s.join(' ')
end
end
Although I'm still running into errors when running the code:
expected: "The Great Gatsby"
got: "the great gatsby"
(compared using ==)
exercise_spec.rb:6:in `block (3 levels) in <top (required)>'
From my beginner's perspective, I cannot see what I'm doing wrong?
Final edit: I just wanted to say thanks for all the effort every one put in in assisting me earlier. I'll show the final working code I was able to produce:
class Title
attr_accessor :string
def initialize(string)
#string = string
end
def fix
word_list = %w{a of and the}
a = string.downcase.split(' ')
b = []
a.each_with_index do |word, index|
if index == 0 || !word_list.include?(word)
b << word.capitalize
else
b << word
end
end
b.join(' ')
end
end
Here's a possible solution.
class Title
attr_accessor :string
IGNORES = %w( the of a and )
def initialize(string)
#string = string
end
def fix
tokens = string.split(' ')
tokens.map do |token|
token = token.downcase
if IGNORES.include?(token)
token
else
token.capitalize
end
end.join(" ")
end
end
Title.new("a title of a book").fix
Your starting point was good. Here's a few improvements:
The comparison is always lower-case. This will simplify the if-condition
The list of ignored items is into an array. This will simplify the if-condition because you don't need an if for each ignored string (they could be hundreds)
I use a map to replace the tokens. It's a common Ruby pattern to use blocks with enumerations to loop over items
There are two ways you can approach this problem:
break the string into words, possibly modify each word and join the words back together; or
use a regular expression.
I will say something about the latter, but I believe your exercise concerns the former--which is the approach you've taken--so I will concentrate on that.
Split string into words
You use String#split(' ') to split the string into words:
str = "a title of a\t book"
a = str.split(' ')
#=> ["a", "title", "of", "a", "book"]
That's fine, even when there's extra whitespace, but one normally writes that:
str.split
#=> ["a", "title", "of", "a", "book"]
Both ways are the same as
str.split(/\s+/)
#=> ["a", "title", "of", "a", "book"]
Notice that I've used the variable a to signify that an array is return. Some may feel that is not sufficiently descriptive, but I believe it's better than s, which is a little confusing. :-)
Create enumerators
Next you send the method Enumerable#each_with_index to create an enumerator:
enum0 = a.each_with_index
# => #<Enumerator: ["a", "title", "of", "a", "book"]:each_with_index>
To see the contents of the enumerator, convert enum0 to an array:
enum0.to_a
#=> [["a", 0], ["title", 1], ["of", 2], ["a", 3], ["book", 4]]
You've used each_with_index because the first word--the one with index 0-- is to be treated differently than the others. That's fine.
So far, so good, but at this point you need to use Enumerable#map to convert each element of enum0 to an appropriate value. For example, the first value, ["a", 0] is to be converted to "A", the next is to be converted to "Title" and the third to "of".
Therefore, you need to send the method Enumerable#map to enum0:
enum1 = enum.map
#=> #<Enumerator: #<Enumerator: ["a", "title", "of", "a",
"book"]:each_with_index>:map>
enum1.to_a
#=> [["a", 0], ["title", 1], ["of", 2], ["a", 3], ["book", 4]]
As you see, this creates a new enumerator, which could think of as a "compound" enumerator.
The elements of enum1 will be passed into the block by Array#each.
Invoke the enumerator and join
You want to a capitalize the first word and all other words other than those that begin with an article. We therefore must define some articles:
articles = %w{a of it} # and more
#=> ["a", "of", "it"]
b = enum1.each do |w,i|
case i
when 0 then w.capitalize
else articles.include?(w) ? w.downcase : w.capitalize
end
end
#=> ["A", "Title", "of", "a", "Book"]
and lastly we join the array with one space between each word:
b.join(' ')
=> "A Title of a Book"
Review details of calculation
Let's go back to the calculation of b. The first element of enum1 is passed into the block and assigned to the block variables:
w, i = ["a", 0] #=> ["a", 0]
w #=> "a"
i #=> 0
so we execute:
case 0
when 0 then "a".capitalize
else articles.include?("a") ? "a".downcase : "a".capitalize
end
which returns "a".capitalize => "A". Similarly, when the next element of enum1 is passed to the block:
w, i = ["title", 1] #=> ["title", 1]
w #=> "title"
i #=> 1
case 1
when 0 then "title".capitalize
else articles.include?("title") ? "title".downcase : "title".capitalize
end
which returns "Title" since articles.include?("title") => false. Next:
w, i = ["of", 2] #=> ["of", 2]
w #=> "of"
i #=> 2
case 2
when 0 then "of".capitalize
else articles.include?("of") ? "of".downcase : "of".capitalize
end
which returns "of" since articles.include?("of") => true.
Chaining operations
Putting this together, we have:
str.split.each_with_index.map do |w,i|
case i
when 0 then w.capitalize
else articles.include?(w) ? w.downcase : w.capitalize
end
end
#=> ["A", "Title", "of", "a", "Book"]
Alternative calculation
Another way to do this, without using each_with_index, is like this:
first_word, *remaining_words = str.split
first_word
#=> "a"
remaining_words
#=> ["title", "of", "a", "book"]
"#{first_word.capitalize} #{ remaining_words.map { |w|
articles.include?(w) ? w.downcase : w.capitalize }.join(' ') }"
#=> "A Title of a Book"
Using a regular expression
str = "a title of a book"
str.gsub(/(^\w+)|(\w+)/) do
$1 ? $1.capitalize :
articles.include?($2) ? $2 : $2.capitalize
end
#=> "A Title of a Book"
The regular expression "captures" [(...)] a word at the beginning of the string [(^\w+)] or [|] a word that is not necessarily at the beginning of string [(\w+)]. The contents of the two capture groups are assigned to the global variables $1 and $2, respectively.
Therefore, stepping through the words of the string, the first word, "a", is captured by capture group #1, so (\w+) is not evaluated. Each subsequent word is not captured by capture group #1 (so $1 => nil), but is captured by capture group #2. Hence, if $1 is not nil, we capitalize the (first) word (of the sentence); else we capitalize $2 if the word is not an article and leave it unchanged if it is an article.
def fix
string.downcase.split(/(\s)/).map.with_index{ |x,i|
( i==0 || x.match(/^(?:a|is|of|the|and)$/).nil? ) ? x.capitalize : x
}.join
end
Meets all conditions:
a, is, of, the, and all lowercase
capitalizes all other words
all first words are capitalized
Explanation
string.downcase calls one operation to make the string you're working with all lower case
.split(/(\s)/) takes the lower case string and splits it on white-space (space, tab, newline, etc) into an array, making each word an element of the array; surrounding the \s (the delimiter) in the parentheses also retains it in the array that's returned, so we don't lose that white-space character when rejoining
.map.with_index{ |x,i| iterates over that returned array, where x is the value and i is the index number; each iteration returns an element of a new array; when the loop is complete you will have a new array
( i==0 || x.match(/^(?:a|is|of|the|and)$/).nil? ) if it's the first element in the array (index of 0), or the word matches a,is,of,the, or and -- that is, the match is not nil -- then x.capitalize (capitalize the word), otherwise (it did match the ignore words) so just return the word/value, x
.join take our new array and combine all the words into one string again
Additional
Ordinarily, what is inside parentheses in regex is considered a capture group, meaning that if the pattern inside is matched, a special variable will retain the value after the regex operations have finished. In some cases, such as the \s we wanted to capture that value, because we reuse it, in other cases like our ignore words, we need to match, but do not need to capture them. To avoid capturing a match you can pace ?: at the beginning of the capture group to tell the regex engine not to retain the value. There are many benefits of this that fall outside the scope of this answer.
Here is another possible solution to the problem
class Title
attr_accessor :str
def initialize(str)
#str = str
end
def fix
s = str.downcase.split(" ") #convert all the strings to downcase and it will be stored in an array
words_cap = []
ignore = %w( of a and the ) # List of words to be ignored
s.each do |item|
if ignore.include?(item) # check whether word in an array is one of the words in ignore list.If it is yes, don't capitalize.
words_cap << item
else
words_cap << item.capitalize
end
end
sentence = words_cap.join(" ") # convert an array of strings to sentence
new_sentence =sentence.slice(0,1).capitalize + sentence.slice(1..-1) #Capitalize first word of the sentence. Incase it is not capitalized while checking the ignore list.
end
end
When trying to find the frequency of letters in 'fantastic' I am having trouble understanding the given solution:
def letter_count(str)
counts = {}
str.each_char do |char|
next if char == " "
counts[char] = 0 unless counts.include?(char)
counts[char] += 1
end
counts
end
I tried deconstructing it and when I created the following piece of code I expected it to do the exact same thing. However it gives me a different result.
blah = {}
x = 'fantastic'
x.each_char do |char|
next if char == " "
blah[char] = 0
unless
blah.include?(char)
blah[char] += 1
end
blah
end
The first piece of code gives me the following
puts letter_count('fantastic')
>
{"f"=>1, "a"=>2, "n"=>1, "t"=>2, "s"=>1, "i"=>1, "c"=>1}
Why does the second piece of code give me
puts blah
>
{"f"=>0, "a"=>0, "n"=>0, "t"=>0, "s"=>0, "i"=>0, "c"=>0}
Can someone break down the pieces of code and tell me what the underlying difference is. I think once I understand this I'll be able to really understand the first piece of code. Additionally if you want to explain a bit about the first piece of code to help me out that'd be great as well.
You can't split this line...
counts[char] = 0 unless counts.include?(char)
... over multiple line the way you did it. The trailing conditional only works on a single line.
If you wanted to split it over multiple lines you would have to convert to traditional if / end (in this case unless / end) format.
unless counts.include?(char)
counts[char] = 0
end
Here's the explanation of the code...
# we define a method letter_count that accepts one argument str
def letter_count(str)
# we create an empty hash
counts = {}
# we loop through all the characters in the string... we will refer to each character as char
str.each_char do |char|
# we skip blank characters (we go and process the next character)
next if char == " "
# if there is no hash entry for the current character we initialis the
# count for that character to zero
counts[char] = 0 unless counts.include?(char)
# we increase the count for the current character by 1
counts[char] += 1
# we end the each_char loop
end
# we make sure the hash of counts is returned at the end of this method
counts
# end of the method
end
Now that #Steve has answered your question and you have accepted his answer, perhaps I can suggest another way to count the letters. This is just one of many approaches that could be taken.
Code
def letter_count(str)
str.downcase.each_char.with_object({}) { |c,h|
(h[c] = h.fetch(c,0) + 1) if c =~ /[a-z]/ }
end
Example
letter_count('Fantastic')
#=> {"f"=>1, "a"=>2, "n"=>1, "t"=>2, "s"=>1, "i"=>1, "c"=>1}
Explanation
Here is what's happening.
str = 'Fantastic'
We use String#downcase so that, for example, 'f' and 'F' are treated as the same character for purposes of counting. (If you don't want that, simply remove .downcase.) Let
s = str.downcase #=> "fantastic"
In
s.each_char.with_object({}) { |c,h| (h[c] = h.fetch(c,0) + 1) c =~ /[a-z]/ }
the enumerator String#each_char is chained to Enumerator#with_index. This creates a compound enumerator:
enum = s.each_char.with_object({})
#=> #<Enumerator: #<Enumerator: "fantastic":each_char>:with_object({})>
We can view what the enumerator will pass to the block by converting it to an array:
enum.to_a
#=> [["f", {}], ["a", {}], ["n", {}], ["t", {}], ["a", {}],
# ["s", {}], ["t", {}], ["i", {}], ["c", {}]]
(Actually, it only passes an empty hash with 'f'; thereafter it passes the updated value of the hash.) The enumerator with_object creates an empty hash denoted by the block variable h.
The first element enum passes to the block is the string 'f'. The block variable c is assigned that value, so the expression in the block:
(h[c] = h.fetch(c,0) + 1) if c =~ /[a-z]/
evaluates to:
(h['f'] = h.fetch('f',0) + 1) if 'f' =~ /[a-z]/
Now
c =~ /[a-z]/
is true if and only if c is a lowercase letter. Here
'f' =~ /[a-z]/ #=> true
so we evaluate the expression
h[c] = h.fetch(c,0) + 1
h.fetch(c,0) returns h[c] if h has a key c; else it returns the value of Hash#fetch's second parameter, which here is zero. (fetch can also take a block.)
Since h is now empty, it becomes
h['f'] = 0 + 1 #=> 1
The enumerator each_char then passes 'a', 'n' and 't' to the block, resulting in the hash becoming
h = {'f'=>1, 'a'=>1, 'n'=>1, 't'=>1 }
The next character passed in is a second 'a'. As h already has a key 'a',
h[c] = h.fetch(c,0) + 1
evaluates to
h['a'] = h['a'] + 1 #=> 1 + 1 => 2
The remainder of the string is processed the same way.
I am trying to write a function that displays a string as alternating upper and lower case letters.
For example:
str= "My name is ballouta!"
==> My NaMe Is BaLlOuTa!
My code is:
def alt_case
flag = 0
str = ''
self.scan(/./) do |b|
if flag == 0
b.upcase ;
flag = 1
str = str + b
else
b.downcase
flag = 0
str = str + b
end #end if
end #end do
str
end #end method
This code returns the string as lower-case ONLY.
"My name is ballouta!"
.gsub(/\w/).with_index{|s, i| i.even? ? s.upcase : s.downcase}
# => "My NaMe Is BaLlOuTa!"
You're using upcase and downcase, both of which return the altered value (which you are not saving and using).
The in-place alternatives upcase! and downcase! may help you out.
Edit: I see #bjhaid suggested pretty much the same solution as mine in a comment well before I posted this. I'll leave my answer up for the explanation I've provided.
Now that your question has been answered, let me suggest a way to change your code to make it more Ruby-like:
class String
def alt_case
split.map { |w| w.chars.map.with_index{ |s,i|
i.even? ? s.upcase : s.downcase }.join }.join(' ')
end
end
"My name is ballouta!".alt_case #=> "My NaMe Is BaLlOuTa!"
Here's how this works:
self #=> "My name is ballouta!" (default receiver)
a = self.split #=> ["My", "name", "is", "ballouta!"]
b = a.map { |w| w.chars.map.with_index{ |s,i|
i.even? ? s.upcase : s.downcase }.join }
#=> ["My", "NaMe", "Is", "BaLlOuTa!"]
b.join(' ') #=> "My NaMe Is BaLlOuTa!"
When computing b, consider the case when w => "name":
c = w.chars #=> ["n", "a", "m", "e"]
d = c.map.with_index{ |s,i| i.even? ? s.upcase : s.downcase }
#=> ["N", "a", "M", "e"]
d.join #=> "NaMe"
I added this method to the String class only because that's what you've done, but in general I wouldn't recommend that; alt_case(string) would be fine.