Forum: Ruby Dynamically create an array

Hi Experts,

I am trying to create an array from hash

example in my hash I have value like


grades =
{ { "subject" => english,
           "Jim" => 94,
           "Billy" => 58
         }

   { "subject" => math,
           "Jim" => 90,
           "Billy" => 80
         }

    {  "subject" => science,
           "Jim" => 99,
           "Billy" => 58
         }

}

now i want to make an array or output like this

94,90,99
58,80,58


i am looking for some help in google but no luck

Robert

Hi,

that "hash" is nowhere near a valid Ruby expression. If this is supposed 
to be an array of hashes (with commas between the elements), use 
Array#map:

jims_grades = grades.map {|grade| grade['Jim']}
p jims_grades

This code is not a valid hash in ruby 1.9.3.
However if I unterstood what you are trying to ask, I would take a look 
at
collect method for your array.

in which may return an array of the return of a given block.

e.g.

grade = {"subject"=>:math, "Jim"=>94, "Billy"=>50}
grade.collect { |key, value| value  } # [:math 94, 50]
grade.collect { |key, value| value unless key == 'subject'  } # [nil, 
94,
50]

later you can use reject method of Array to remove the nil values.


2012/12/10 robert lengu <lists@ruby-forum.com>

>            "Billy" => 58
>          }
>
> Robert
>
> --
> Posted via http://www.ruby-forum.com/.
>
>


--
Pedro Henrique de Souza Medeiros
----------------------------------
Cel: +55 (61) 9197-0993
Email: pedrosnk@gmail.com

Beautiful is better than ugly,
Explicit is better than implicit,
Simple is better than complex,
Complex is better than complicated.

The Zen of Python, by Tim Peters

grades = [
  { "subject" => "english",
    "Jim" => 94,
    "Billy" => 58
  },

  { "subject" => "math",
    "Jim" => 90,
    "Billy" => 80
  },

  {  "subject" => "science",
     "Jim" => 99,
     "Billy" => 58
  },

]

jim = []
billy = []

grades.each do |hash|
  jim << hash['Jim']
  billy << hash['Billy']
end

p jim
p billy

--output:--
[94, 90, 99]
[58, 80, 58]

In this type of case I'd strongly suggest looking into making a class 
for
subject, it saves quite a bit of time in the long run versus a hacked
together hash. As more grades and subjects are added the Hash will 
become
slower and more confounded to use.

I also don't entirely understand the reasoning behind your layout. 
Subject
should not be on the same level with the student/grade pair. It doesn't
make sense in that manner. If we put it in bullet points it's a little
clearer:

*BAD*


   - Grades
      - Subject
      - Student
         - Grade


*GOOD*
*
*

   - Grades
      - Subject
         - Students


Again, the current hierarchy makes no sense. and it would be far easier 
to
manipulate with a clearer structure that cleanly separates different 
types
of data.

The basic frame for a class would be: Grades contain many subjects, each
with several students that all have one grade. This can easily change of
course, but with the one grade system it works.