I would like to ask you how can I match a nil value in a hash, e. g.:
aAnimals = {1=>'dog', 2=>'cat'}
puts laAnimals[1] # dog
puts laAnimals[2] # cat
puts laAnimals[3] # nil
how can I put 'no animal' in case of nil values or higher than lenght of the matrix, e.g.:
laAnimals = {1=>'dog', 2=>'cat'}
laAnimals.default = 'no animal'
puts laAnimals[1] # dog
puts laAnimals[2] # cat
puts laAnimals[3] # no animal
I want something like that: laAnimals = {1=>'dog', 2=>'cat', default='no animal'}...it is possible?
From http://ruby-doc.org/core-2.2.0/Hash.html
Hashes have a default value that is returned when accessing keys that
do not exist in the hash. If no default is set nil is used. You can
set the default value by sending it as an argument to ::new:
So in your case using laAnimals = Hash.new("no animal") will use the string no animal as the default value.
Exupery's answer is correct, but if you don't have access to the creation of the hash you're working with, you can use Hash#fetch (docs).
laAnimals = {1=>'dog', 2=>'cat'}
puts laAnimals.fetch(1, 'no animal') # dog
puts laAnimals.fetch(2, 'no animal') # cat
puts laAnimals.fetch(3, 'no animal') # 'no animal'
I personally prefer this way of accessing hashes, because if the key (in your example, 1, and 2) is not present it will raise an exception.
Related
I know writing like
a=23
p "the value of a is #{a}"
it will print: the value of a is 23.
but now I am actually receiving this string as a parameter like
def evaluate string
a=23
puts string
end
calling method pass that string as a parameter
evaluate "the value of a is #{a}"
Is there any way to evaluate this string inside the method? puts string has to interpolate the value a=23.
Edit:
I have to read and execute the program from Excel.
At the first line,
Excel entry is,
"id=something" setvalue a
So now corresponding program will read the value from locator id=something and set it into the instance variable #a.
and user's next excel entry would be
"the value of a is 23" compare "the value of a is #{a}"
Now the program will read "the value of a is 23" and this "the value of a is #{a}" for comparison, but before it compares, it has to replace the value a. That's all I want. I hope now my question is very clear.
For ruby you can change how you "format" your strings in Excel, than you can use "classic" formatting
a = 23
s = 'the value of a is %s'
def evaluate(text, value)
puts text % value
end
You can use different formatting keys, for example %d for integers, %f for float numbers
You can use named arguments
dynamic_text = 'the value of the %<product_name>s is %<product_price>0.2f'
def evaluate(text, args)
puts text % args
end
name = "Product"
price = 78.99
evaluate dynamic_text, product_name: name, product_price: price
Without names, use order of the given values
dynamic_text = 'the value of the %s is %0.2f'
def evaluate(text, args)
puts text % args
end
name = "Product"
price = 78.99
evaluate dynamic_text, [name, price]
You can make a block and then evaluate the string:
def evaluate &block
a=23
block.call(a)
end
evaluate { |a| "the value of a is #{a}" } #=> "the value of a is 23"
It's a very odd thing you're attempting to do. When you have some sort of a pattern with placeholders, you do it like:
def evaluate(string)
a=23
format string, a: a
end
evaluate "the value of a is %{a}"
String interpolation with #{..} is not meant for the case you're describing as the value is evaluated at the time of constructing the string, not later. You could do some regexp matching and replace the #{..} with %{..} as a workaround.
There's a few ways:
"Code" Dynamic
lazy evaluation with lambdas:
def evaluate(str_template)
a = 23
str_template.call(a)
end
user_input = gets
my_lambda = lambda do |str|
user_input.size > 10 ? "dynamic 1 #{str}" : "dynamic 2 #{str}"
end
evaluate(my_lambda)
# => "dynamic 1/2 23"
This is "code dynamic", but not "input dynamic", i.e. you can't receive the string template from the user.
"Input" Dynamic 1
ERB templating:
require 'erb'
user_input_erb = gets
puts user_input_erb # "Hello <%= name %>"
name = gets # also user input, e.g. "World"
ERB.new(user_input_erb).result
# => "Hello World"
Note that in general, getting string templates from the user and evaluating them is a potential security vulnerability. If there's any possibility user input can be adversarial, you'll want to see if you can find a "guaranteed to be safe against all user input" string templating library.
"Input" Dynamic 2
user_input_template = gets
puts user_input_template # "Hello %s"
name = gets # also user input, e.g. "World"
user_input_template % name
# => "Hello World"
"Input" Dynamic 3
Really dangerous, but:
user_input_ruby_code = gets
puts user_input_ruby_code # '"Hello #{name}"'
name = gets # also user input, e.g. "World"
eval user_input_ruby_code # DANGER
# => "Hello World"
Player = Struct.new(:reference, :name, :state, :items, :location)
# Setting game initials
game_condition = 0
player = Player.new(:player, "Amr Koritem", :alive, [:knife, :gun])
puts player.name
player.location = :jail5
class Dungeon
attr_accessor :player, :rooms, :prisoners, :gangsmen, :policemen
##counter = 0
def initialize(player)
#player = player
end
end
my_dungeon = Dungeon.new(player)
if my_dungeon.player.location.to_s.scan(/\D+/) == "jail"
puts "yes"
end
This code is supposed to print "yes" on the screen, but it doesn't. I changed the == sign to != and surprisingly it printed "yes" !
I thought may be I understood the regular expression wrong so I typed this code:
puts my_dungeon.player.location.to_s.scan(/\D+/)
It prints "jail" on the screen, which means I wasn't wrong, was I ?
Can anyone explain this please ?
As Wiktor's comment says, arrays are always truthy, and scan always returns an array, even if there are no matches. Instead you can use any of the following methods:
str = "jail5"
if str[/\D+/] # => nil or the match contents
if str.match /\D+/ # => nil or MatchData object
if str =~ /\D+/ # => nil or index of the match
unless str.scan(/\D+/).empty?
if str.scan(/\D+/).length > 0
In general when you come across surprising behavior like this you should do a bit of introspection - check what the result value is using print or a breakpoint.
I created a method to count a substring 'e' in a string passed as an argument. If there isn't a substring 'e' in the string, it should return "There is no \"e\"." I am trying to achieve this:
How many times 'e' is in a string.
If given string doesn't contain any "e", return "There is no "e"."
if given string is empty, return empty string.
if given string is nil, return nil.
This is my code:
def find_e(s)
if !s.include?("e")
"There is no \"e\"."
elsif s.empty?
""
else s.nil?
nil
end
s.count("e").to_s
end
find_e("Bnjamin")
It skips the if statement and it still uses the method count. Why is this?
To achieve what you want you could move your string.count to the else statement in your if, because actually you're making your method return the quantity of e passed in the count method over your string, but what happens inside the if isn't being used:
def find_e(s)
if s.nil?
nil
elsif s.empty?
''
elsif !s.include?("e")
"There is no \"e\"."
else
s.count("e").to_s
end
end
p find_e("Bnjamin") # => "There is no \"e\"."
p find_e("Benjamin") # => "1"
p find_e(nil) # => nil
p find_e('') # => ""
And also your validations must be in order, first check nil values, then empty values, and then the rest, if you don't then you'll get some undefined method ___ for nil:NilClass errors.
You might have a hard time using the method you wrote. In the next method, you'll need a new case statement to test if find_e returned nil, an empty string, a string with a number or "no e".
This method would be a bit more consistent:
def count_e(string_or_nil)
count = string_or_nil.to_s.count("e")
if count == 0
"There is no \"e\"."
else
count
end
end
puts count_e("Covfefe")
# 2
puts count_e("Bnjamin")
# There is no "e".
puts count_e("")
# There is no "e".
puts count_e(nil)
# There is no "e".
But really, if there's no e in the input, just returning 0 would be the most logical behaviour.
You need to put your count method in a branch of the if/else statement, or else it will be evaluated last every time. Without an explicit return statement Ruby will return the last statement, so putting the method outside the if/else branch on the last line guarantees it will always be hit. Also, nil can be converted to an empty string by calling #to_s, so you can remove one of your branches by converting s.to_s, calling empty? and returning s
def find_e(s)
if s.to_s.empty?
s
elsif !s.include?("e")
"There is no \"e\"."
else
s.count("e").to_s
end
end
If you just return 0 whether you get nil, an empty string, or a string without e, you can make it one line
def find_e(s)
s.to_s.count("e").to_s
end
If it were me I'd probably return an Integer, which can always be converted to a String later. puts and "#{}" will implicitly call to_s for you anway. Then you can use that integer return in your presentation logic.
def count_e(input)
input.to_s.count("e")
end
def check_for_e(input)
count = count_e(input)
count > 0 ? count.to_s : "There's no \"e\"."
end
check_for_e("Covfefe") # => "2"
check_for_e("Bnjamin") # => "There's no \"e\"."
check_for_e(nil) # => "There's no \"e\"."
check_for_e("") # => "There's no \"e\"."
In Ruby, methods return the last statement in their body. Your method's last statement is always s.count("e").to_s, since that lies outside of the if statements.
i am working though LearnTocodethehardway.com http://ruby.learncodethehardway.org/book/ex25.html
On ex25. In the example there is a module that has a bunch of methods that return or print values. The Print_last_word method when supplied with an array of strings just puts nil. it does this even in his example output. My question would then be why?
To be precise, it doesn't puts nil - it puts the last word and returns nil. Here's the example output:
>> Ex25.print_last_word(words)
wait. # <- this is the output
=> nil # <- this is the return value
puts always returns nil.
UPDATE
There seems to be a bug in print_first_word:
module Ex25
def Ex25.print_first_word(words)
word = words.pop(0)
puts word
end
end
Ex25.print_first_word(["foo", "bar", "baz"])
#=> nil
This is because ["foo", "bar", "baz"].pop(0) returns an empty array and puts [] just returns nil without printing anything.
A working implementation (in the exercise's style) could look like this:
module Ex25
def Ex25.print_first_word(words)
word = words.shift
puts word
end
end
To make it more easy to understand:
"puts" never is used for its return value. It is used for its side effect if you wanted a method that would return a word, you would then do something with that word.
words = ["apple", "cucumber", "apple"]
def give_me_first_word(array_of_words)
array_of_words.first
end
variable_to_be_used_later = give_me_first_word(words)
This function would return "apple"(and in this case the variable would be assigned "apple"), but it would puts nothing to the screen. This value would then be used in another program or function.
If you puts a value, you would then not need to return it to any other program as it's already served its purpose. It's actually intuitive because if puts also returned the value, it would be doing two things. The counterpart to "puts" would be "return" that simply returns the value and does not display it to the screen.
I'm doing my first program, a simple to-do list. I want it to let me type a number, and delete the corresponding item from the list.
Every time though, I get "no implicit conversion from nil to integer". I can't seem to work it out. Any ideas?
$list = Array.new
def mainmethod
puts "Enter new item, or type 'view' to view the list, 'delete' to delete items"
input = gets.chomp
if input.downcase == "view"
puts "Your to do list is as follows:"
puts $list
elsif input.downcase == "delete"
puts "Which item would you like to delete? (Enter a number)"
deletenumber = gets.chomp.to_i
deletenumber-=1
delete_list = [deletenumber]
delete_list.each do |del|
$list.delete_at($list.index(del))
end
else
$list << input
puts "Added to list!"
end
end
loop { mainmethod }
See http://www.ruby-doc.org/core-1.9.3/Array.html#method-i-delete_at for the proper way of using Array#delete_at.
What you do is calling #index with a number that your array does not contain. Therefore $list.index(del) will return nil and the call to #delete_at will fail.
What you need to do is $list.delete_at(del).
The error TypeError: no implicit conversion from nil to integer happens when you try to access an element of an array using nil as the index. In your case it looks like delete_at is being passed nil:
[ 1, 2, 3 ].delete_at(nil)
# => TypeError: no implicit conversion from nil to integer