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In this challenge you must implement the method code that receives a string with a mathematical calculation and returns the value that ? must have for the account result to be correct.
'100 + ? + 3 = 108'
How to find ? value in ruby.
can someone explain how to solve?
Computers are really dumb and need to be told what to do.
Try solving the problem yourself by hand and when it's very clear for you how to solve it, try to implement it.
I'll give you a start
Validate if the input is empty or nil
Split the input into its parts '100 + ? + 3 = 108' => ["100", "+", "?", "+", "3", "=", "108"] (you can put them in an array)
Check if each part is a number, an operator or a ?
If it's a number, transform it from string to number
if It's an operator check which one, +, -, etc. and then act on it taking left and right side of the operator
etc. etc
You'll notice it's not trivial, but eventually each one of those paragraphs can be translated into specific ruby code.
Give it a try and ask again when you get stuck.
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EDIT: ok, I misunderstood the task. sorry.
I really can't find anything else on the web and don't get it myself.
I want to to delete the odd-numbered entries from an array of integers with a method in Ruby. But I get only errors right at the point where I define the method. How can I make the method understand this?
def even
a=[]
i=0
while i<=a.length
a[i]%2 == 1
a.delete(a[i])
i+=i
end
end
even([1,2,3])
You can simply use Ruby array reject method like below,
arr = [1,2,3,4,5,6,7,8]
arr.reject{|v| v%2 == 1}
# => [2, 4, 6, 8]
in ruby it is usually easier to think in a more functional way. In your case, you want to iterate through the list of elements, selecting the ones that are even. To iterate through a list and select elements using a predicate, use select. A number already has a method to check if it is even (even?). So the solution is quite simple:
[1,2,3].select(&:even?)
that returns a new list with only the even numbers. If you want to modify the list in place, use select! instead.
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I was wondering if there was a way to reference an object when assigning it to a variable. Here is an example of where this question would apply:
Let's say I wanted to assign the substring of a regex to a variable, call it i.
To assign, I could write
i = /some_regex/.to_s
and then
i = i[3...i.length]
I could also write it all in one line, like
i = /some_regex/.to_s[3.../some_regex/.to_s.length]
However, both of these examples seem somewhat redundant and the second approach could become unwieldy with big regex's or multiple method calls. Is there a way to reference the object being changed without having to rewrite everything?
Edit: Sorry for previous ambiguity.
Ruby evaluates the right side of the equals sign before setting the left side equal to it, so if i already exists you can do what you're talking about. A simple example:
i = 10
i = i + 1 # now i = 11
However, you can't use i to define itself. You could use the following two lines:
i = expression.match(/\d+[\+|-|\*|\/]/)
i = i[0..i.length - 1] # Note: this is the same as i = i[0...i.length]
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Take an existing list of strings with whole and fractions of inch that includes the inch symbol:
['1"','1/2"','1 1/4"','1/4"','2"','1 1/8"']
Is there a best (rubyish, elegant, use of methods, object oriented) way in ruby to sort so it becomes
['1/4"','1/2"','1"','1 1/8"','1 1/4"','2"']
String#to_r will conveniently ignore trailing garbage (such as "):
The parser ignores leading whitespaces and trailing garbage.
so converting something like '1 1/2"' to a number that will compare sensibly is a simple matter of:
s = '1 1/2"'
r = s.split.map(&:to_r).inject(:+)
Split the string into pieces, convert each to a Rational using String#to_r, and then add them up using Enumerable#inject with a symbol argument. Clean and easy.
Once you have that, sorting is trivial:
array = ['1"','1/2"','1 1/4"','1/4"','2"','1 1/8"']
rationalized = lambda { |s| s.split.map(&:to_r).inject(:+) }
sorted = array.sort_by(&rationalized)
You don't have to use a lambda of course:
array.sort_by { |s| s.split.map(&:to_r).inject(:+) }
but I find that naming your little snippets of logic clarifies things.
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The following shows that when I use the to_f method to covert a string to a floating point number and the last decimal point is dropped. How can preserve all decimal points in a given number?
irb(main):002:0> value='1.7.8'
=> "1.7.8"
irb(main):003:0> value.to_f
=> 1.7
Some context:
I am writing the the value to a file and If I write it as a string I get the quotes '1.7.8'. What I am looking for infact is 1.7.8. Hope that makes sense.
EDIT:
I see the error in my question so I'm trying to close it however I can only vote to close it.
just to clarify what I've found is actually contrary to what I said above.
turns out if I write the string '1.7' to a file it is written as '1.7' but with the string '1.7.8' it is written as 1.7.8. I'm just trying to understand why this is occurring.
To write it to a file simply write it like so:
value = "1.7.8"
File.open("file") { |f| f.puts("#{value}") }
The string in the file will not have quotes around it.
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I've go a string made in this way.
"AABBCCDD....." grouped by 4 with variable lenght.
I need a method that swap that 2 by two the chars in this string
def swap2_by_2( string )
???
end
If the input is AABBCCDD the output will be BBAADDCC
Thanks, i'm very noob in ruby.
Edit: my mistake, a more comprhensive example may be.. Input: ABCDEFGH -> CDABGHEF
It is not clear what the OP is trying to do, but if it is to flip the first and the second characters with the third and fourth characters for every four characters, then the example that the OP showed is highly misleading and inappropriate (It should have been "ABCD..." instead of "AABB..."). In that case, a solution would be:
string.gsub(/(..)(..)/, '\2\1')
Thinking about your question, an interpreting the "ABCDEF", I am sure, that you are looking for pack / unpack in Ruby: I found a good page here How to change bit order in Ruby
And here are two a non-regexp versions:
p 'AABBCCDD'.chars
.each_slice(2)
.each_slice(2)
.map(&:reverse)
.join
#=> "BBAADDCC"
# or
'AABBCCDD'.chars
.each_slice(4)
.map{|x| x.rotate(2)}
.join