With Ranges in Ruby you can do 0..5 to include all numbers between and including 0 and 5. You can also do 0...5 to include the same numbers except 5 is not included.
(1..5) === 5
=> true
(1...5) === 5
=> false
(1...5) === 4.999999
=> true
Is there a way to exclude the first number instead of the last to get a result like this?
(1...5) === 1
=> false
(1...5) === 1.00000001
=> true
No, there is no built-in support for such a range. You might want to roll your own Range-like class if this behavior is necessary.
Not natively with a Range. You can mess with its mind but you're better off using an incremented first value. This is ugly but:
[(1..5).to_s].map{ |s| a,b=s.split('..').map{|i| i.to_i}; (1+a .. b) } #=> [2..5]
or
Range.new(*[(1..5).to_s].map{ |s| a,b=s.split('..').map{|i| i.to_i}; [1+a,b] }.flatten) #=> 2..5
or
irb(main):004:0> asdf = (1..5)
=> 1..5
irb(main):005:0> Range.new(asdf.min.succ, asdf.max)
=> 2..5
None seem overly elegant.
Besides just sending first_arg.succ instead of first_arg? No, there is no special support for this.
You could monkey patch Range to add a method to behave the way you want. Ex:
class Range
def exclusive()
Range.new(self.first+1, self.last-1)
end
end
(1..5).exclusive === 5
==>false
(1..5) === 5
==>true
Beware of monkeypatching though, as it changes the functionality of existing classes. There is probably a better way to do it in this case, but given the question, this is an acceptable answer.
Related
I was trying to be clever about deterministically picking random stuff, and found this:
irb(main):011:0> Random.new(Random.new(1).rand + 1).rand == Random.new(1).rand
=> true
irb(main):012:0> Random.new(Random.new(5).rand + 1).rand == Random.new(5).rand
=> false
irb(main):013:0> Random.new(Random.new(5).rand + 5).rand == Random.new(5).rand
=> true
For a second, I thought "wow, maybe that's a property of random number generators", but Python and C# fail to reproduce this.
You’re probably going to be disappointed with this one. Let’s take a look at the output of rand:
irb(main):001:0> Random.rand
0.5739704645347423
It’s a number in the range [0, 1). Random.new accepts an integer seed.
irb(main):002:0> Random.new(5.5) == Random.new(5)
true
Mystery solved!
I'm trying to express a condition like this:
if 33.75 < degree <= 56.25
# some code
end
But Ruby gives this error:
undefined method `<=' for true:TrueClass
I'm guessing that one way to do it is something like:
if 33.75 < degree and degree <= 56.25
# code
end
But there is no another, easier way?
Ruby also has between?:
if value.between?(lower, higher)
There are many ways of doing the same things in Ruby.
You can check if value is in the range by use of following methods,
14.between?(10,20) # true
(10..20).member?(14) # true
(10..20).include?(14) # true
But, I would suggest using between than member? or include?. You can find more about it here.
You can express a <= x <= b as (a..b).include? x and a <= x < b as (a...b).include? x.
>> (33.75..56.25).include? 33.9
=> true
>> (33.75..56.25).include? 56.25
=> true
>>
>> (33.75..56.25).include? 56.55
=> false
Unfortunately, there seems no such thing for a < x <= b, a < x < b, ..
UPDATE
You can accomplish using (-56.25...-33.75).include? -degree. But it's hard to read. So I recommend you to use 33.75 < degree and degree <= 56.25.
use between? is the easiest way, I found most answers here didn't mention (ruby doc explanation is hard to understand too), using between? does INCLUDE the min and max value.
for example:
irb(main):001:0> 2.between?(1, 3)
=> true
irb(main):002:0> 3.between?(1, 3)
=> true
irb(main):003:0> 1.between?(1, 3)
=> true
irb(main):004:0> 0.between?(1, 3)
=> false
by the way, ruby doc quote:
between?(min, max) → true or false Returns false if obj <=> min is
less than zero or if anObject <=> max is greater than zero, true
otherwise.
undefined method `<=' for true:TrueClass
means that Ruby is not parsing your if-condition the way you expect it.
Using && and adding parentheses helps!
if (33.75<degree) && (degree<=56.25)
...
end
It's a bad habit to leave out parentheses -- as soon as the expression gets more difficult, you could get a surprising outcome. I've seen this many times in other people's code.
Using and instead of && in Ruby is a very bad idea, see:
https://www.tinfoilsecurity.com/blog/ruby-demystified-and-vs
http://rubyinrails.com/2014/01/30/difference-between-and-and-in-ruby/
You can also use this notation:
(1..5) === 3 # => true
(1..5) === 6 # => false
Adjust value to range?
value = 99
[[value,0].max, 5].min # 5
value = -99
[[value,0].max, 5].min # 0
value = 3
[[value,0].max, 5].min # 3
I have a exercise of the school and i can't resolve it. Can you help me?
The problem is this:
Try using a method that takes two arguments - use the between? method
to determine if the number 2 lies between the numbers 1 and 3.
I tried to find what is the .between? method but í couldn't find it.
I just know that is a method
The method is Comparable#between?, and you can use it like this:
2.between?(1, 3)
# => true
use between? is the easiest way, I found most answers here didn't mention (ruby doc explanation is hard to understand too), using between? does INCLUDE the min and max value.
for example:
irb(main):001:0> 2.between?(1, 3)
=> true
irb(main):002:0> 3.between?(1, 3)
=> true
irb(main):003:0> 1.between?(1, 3)
=> true
irb(main):004:0> 0.between?(1, 3)
=> false
by the way, ruby doc quote (too hard to understand for newbie):
between?(min, max) → true or false Returns false if obj <=> min is
less than zero or if anObject <=> max is greater than zero, true
otherwise.
From "between" ruby documentation:
between?(min, max) → true or false
Returns false if obj <=> min is less than zero or if anObject <=> max is greater than zero, true otherwise.
Uh oh, and of course, it's #=== method for ranges:
( 1..3 ) === 2 #=> true
( 1..3 ) === 4 #=> false
You can use Range#cover? as a solution :
(1..3).cover? 2 #=> true
Is there a simple way in Ruby to get a true/false value from something without explicitly evaluating it to true or false
e.g. how would one more succinctly express
class User
def completed_initialization?
initialization_completed == 1 ? true : false
end
end
is there some way to do something along the lines of
initialization_completed.true?
There's obviously not much in it but since I'm in the zen garden of Ruby I might as well embrace it
EDIT (I've updated the example)
This question was extremely badly phrased as was very gently pointed out by #Sergio Tulentsev. The original example (below) does of course evaluate directly to a boolean. I'm still struggling to find an example of what I mean however Sergio's double-negative was in fact exactly what I was looking for.
Original example
class User
def top_responder
responses.count > 10 ? true : false
end
end
> operator already returns boolean value. So it can be just
def top_responder
responses.count > 10
end
To convert arbitrary values to booleans, I offer you this little double-negation trick.
t = 'foo'
!!t # => true
t = 1
!!t # => true
t = 0
!!t # => true
t = nil
!!t # => false
The first negation "casts" value to boolean and inverts it. That is, it will return true for nil / false and false for everything else. We need another negation to make it produce "normal" values.
How can I get the opposite of a boolean in Ruby (I know that it is converted to 0/1) using a method inline?
say I have the given instance:
class Vote
def return_opposite
self.value
end
end
Which obviously doesn't do anything, but I can't seem to find a method that is simple and short something like opposite() or the like. Does something like this exist and I'm just not looking at the right place in the docs? If one doesn't exist is there a really short ternary that would toggle it from 1 => 0 or 0 => 1?
I like to use this
#object.boolean = !#object.boolean
Boolean expressions are not 0 or 1 in Ruby, actually, 0 is not false
If n is numeric we are swapping 0 and 1...
n == 0 ? 1 : 0 # or...
1 - n # or...
[1, 0][n] # or maybe [1, 0][n & 1] # or...
class Integer; def oh_1; self==0 ? 1:0; end; end; p [12.oh_1, 0.oh_1, 1.oh_1] # or...
n.succ % 2 # or...
n ^= 1
If b already makes sense as a Ruby true or false conditional, it's going to be hard to beat:
!b
These examples differ in how they treat out-of-range input...
You can use XOR operator (exclusive or)
a = true
a # => true
a ^= true
a # => false
a ^= true
a # => true
Edit: See comment by #philomory below.
I believe this is basically an oversight in the boolean classes (TrueClass and FalseClass) in Ruby.
You can negate any object:
nil.! => true
false.! => true
true.! => false
0.! => false
1.! => false
a.! => false (all other objects)
But you cannot in-place negate the boolean objects:
a.!! => does not compile
I guess this would call for trouble with the compiler's grammar.
The best you can do, is thus:
a = a.!
If you just want to access the opposite of the value, use ! as some people have said in the comments. If you want to actually change the value, that would be bool_value = !bool_value. Unless I've misunderstood your question. Which is quite possible.
In order to toggle a boolean data in rails you can do this vote.toggle!(:boolean)
If you want to toggle boolean (that is false and true) , that would be as simple as just use ! as others has stated.
If you want to toggle between 0 and 1 , I can only think of something naive as below :)
def opposite
op = {0=>1,1=>0}
op[self.value]
end
In a Rails app, I use this method to toggle a post between paused and active, so ! (not) is my preferred method.
def toggle
#post = Post.find(params[:id])
#post.update_attributes paused: !#post.paused?
msg = #post.paused? ? 'The post is now paused.' : 'The post is now active.'
redirect_to :back, notice: msg
end
I think that using a ternary can be interesting :
check = false
check == true ? check = false : check = true