Dynamically create an array

Ruby
1

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

2

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

3

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]

4

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.

5

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 [email protected]

       "Billy" => 58
     }

Robert

–
Posted via http://www.ruby-forum.com/.

–
Pedro Henrique de Souza Medeiros

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Email: [email protected]

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