New to Ruby some problems

ruby-talk
1

I am new to Ruby, My mother tongue is C++ .. I have too many problems I
hope you'd help me with that in the 2 short attached files .. thank you
very much :slight_smile:

Attachments:
http://www.ruby-forum.com/attachment/6536/2Dto1D.rb
http://www.ruby-forum.com/attachment/6537/Complex.rb

···

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2

First, fix the syntax errors. You are missing commas in some of your method definitions and adding spaces after the '@' character in your instance variables. There may be other issues, but the Ruby runtime should point them out to you when you try to load and execute your code.

To answer your question about adding a setter/getter for the MATRIX class, you could define # and #= for that purpose to delegate to your @array ivar.

e.g.

def (index)
  @array[index]
end

def =(index, value)
  @array[index] = value
end

Hope this helps. Welcome to Ruby!

cr

···

On Aug 22, 2011, at 8:32 AM, jack jones wrote:

I am new to Ruby, My mother tongue is C++ .. I have too many problems I
hope you'd help me with that in the 2 short attached files .. thank you
very much :slight_smile:

Attachments:
http://www.ruby-forum.com/attachment/6536/2Dto1D.rb
http://www.ruby-forum.com/attachment/6537/Complex.rb

3

With Ruby, you should try to aim for terse and simple code.

This here:

  def array
    return @array
  end

Can be rewritten as:

  attr_reader :array

In class MATRIX.

Also you can omit 'return'. I use that especially for short methods.

···

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4

I am sorry I can't fix the errors though :S:S!

Attachments:
http://www.ruby-forum.com/attachment/6538/2Dto1D.rb

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5

I tried to read it but I couldn't understand a word I am sorry

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6

Thank you very much Chuck Remes :slight_smile:
The problem is I don't understand those functions :
# now name just [] = ?? The problem is that I don't get the magic
    10 def []=(row, column, value) # how does it works?
    11 position = index row, column
    12 @array[position] = value
    13 end
    15 # retrieve value from row, column
    16 def [](row, column)
    17 position = index row, column
    18 return @array[position]
    19 end

···

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7

First of all thank you very much 7stud :slight_smile:
okay I got the method but I had a question how would Ruby know what's in
the [ ] and what's out of them
for example :

class Dog
  @array = []
  def []=(arg1, arg2, arg3)
    array[arg1 + arg2] = arg3 # any operation
  end
end

d = Dog.new
d.abc('hello')
d.[1,2]= 3
# or
d.[1] = 2, 3
# we have 3 args where to put each??
# another thing what if I have more than one array
# I'll have to define the method name as def array1[]= (arg1, arg2,
arg3)
# that would be right or wrong??

···

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8

thank you all very much :slight_smile:

···

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9

Sorry, I didn't read the problem closely enough (too early in the morning!). You need to pass a ROW and COLUMN to set or get a value in your matrix instead of just a single value like I posted above.

Something like this might be a good start (untested).

class Matrix
  def initialize(rows, cols)
    @array =
    @rows, @cols = rows, cols
  end

  def set(x, y, value)
    @array[index(x, y)] = value
  end

  def get(x, y)
    @array[index(x,y)]
  end

private

  def index(x, y)
    (x * @cols) + y
  end
end

···

On Aug 22, 2011, at 8:53 AM, Chuck Remes wrote:

On Aug 22, 2011, at 8:32 AM, jack jones wrote:

I am new to Ruby, My mother tongue is C++ .. I have too many problems I
hope you'd help me with that in the 2 short attached files .. thank you
very much :slight_smile:

Attachments:
http://www.ruby-forum.com/attachment/6536/2Dto1D.rb
http://www.ruby-forum.com/attachment/6537/Complex.rb

First, fix the syntax errors. You are missing commas in some of your method definitions and adding spaces after the '@' character in your instance variables. There may be other issues, but the Ruby runtime should point them out to you when you try to load and execute your code.

To answer your question about adding a setter/getter for the MATRIX class, you could define # and #= for that purpose to delegate to your @array ivar.

e.g.

def (index)
@array[index]
end

def =(index, value)
@array[index] = value
end

10

Jack, please ask some specific questions. We are all more than willing to help.

You already have a set of code that you are trying to run. The code is riddled with syntax errors that the runtime is highlighting for you. We aren't going to fix up every last detail for you; as a C++ coder you are probably acclimated to handling much weirder errors and fixing them. The errors given by the Ruby runtime should be more than sufficient for you to fix them.

With those fixes and some of the suggestions given in this thread, you should be much further along. What's next?

cr

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On Aug 22, 2011, at 10:56 AM, jack jones wrote:

I tried to read it but I couldn't understand a word I am sorry

11

when in ruby, think in ruby.
when new in language, start slowly, a line of code at a time, rtfm.

try eg,

$ cat -n test_matrix.rb
     1 # This is a program to store a two dimension array into one
dimension only .. ROW major
     2 class MATRIX
     3 attr_reader :array
     4 def initialize(rows, cols)
     5 @cols = cols
     6 @array = Array.new(rows*cols){ rand(10)}
     7 end
     8
     9 # set desired row and column and value
    10 def =(row, column, value)
    11 position = index row, column
    12 @array[position] = value
    13 end
    14
    15 # retrieve value from row, column
    16 def (row, column)
    17 position = index row, column
    18 return @array[position]
    19 end
    20
    21 private
    22 def index row, column
    23 return (row-1) * @cols + (column-1) # ruby array index starts at 0
    24 end
    25 end
    26
    27
    28 mat = MATRIX.new(2,2)
    29 puts "before"
    30 p mat.array
    31
    32 puts "after"
    33 mat[1,1]=11
    34 mat[1,2]=12
    35 mat[2,1]=21
    36 mat[2,2]=22
    37
    38 puts mat[1,1]
    39 puts mat[1,2]
    40 puts mat[2,1]
    41 puts mat[2,2]
    42
    43 p mat.array
    44
    45

$ ruby test_matrix.rb
before
[5, 8, 6, 4]
after
11
12
21
22
[11, 12, 21, 22]

kind regards -botp

···

On Mon, Aug 22, 2011 at 11:26 PM, jack jones <shehio_22@hotmail.com> wrote:

I am sorry I can't fix the errors though :S:S!

Attachments:
http://www.ruby-forum.com/attachment/6538/2Dto1D.rb

12

jack jones wrote in post #1018220:

Thank you very much Chuck Remes :slight_smile:
The problem is I don't understand those functions :
# now name just = ?? The problem is that I don't get the magic
    10 def =(row, column, value) # how does it works?
    11 position = index row, column
    12 @array[position] = value
    13 end
    15 # retrieve value from row, column
    16 def (row, column)
    17 position = index row, column
    18 return @array[position]
    19 end

'=' is actually a method. Does that help?

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13

I don't think we can teach you the entire language on this mailing list.

I recommend you take a look at a few books.

These are very good but cost a few $$.

http://amzn.to/qWRLUg

Here's a free one but it's a tad out of date (really only covers Ruby 1.8).

http://mislav.uniqpath.com/poignant-guide/

Work through the examples. When you get stuck or confused, drop a note here and we'll try to help.

cr

···

On Aug 25, 2011, at 7:34 AM, jack jones wrote:

First of all thank you very much 7stud :slight_smile:
okay I got the method but I had a question how would Ruby know what's in
the and what's out of them
for example :

class Dog
@array =
def =(arg1, arg2, arg3)
   array[arg1 + arg2] = arg3 # any operation
end
end

d = Dog.new
d.abc('hello')
d.[1,2]= 3
# or
d.[1] = 2, 3
# we have 3 args where to put each??
# another thing what if I have more than one array
# I'll have to define the method name as def array1= (arg1, arg2,
arg3)
# that would be right or wrong??

14

[]= operator can take either two three arguments - they're written
like this: array[a, b] = c or array[a] = b (this is the same as
array.[]=(a, b, c) or array.[]=(a, b) ).

See the docs for this method to see why are the three arguments
needed: http://www.ruby-doc.org/core/classes/Array.html#M000219

-- Matma Rex

15

I just wanted to point out something that I think hasn't been
mentioned. In the "assignment-like" methods, where Ruby applies
syntactic sugar so that you can use the usual syntax, Ruby also does
something that is not the same as with other method calls: the result
of the "assignment" expression is the expression's right hand side,
not the result value of the method:

ruby-1.8.7-p334 :001 > class A
ruby-1.8.7-p334 :002?> def = a,b
ruby-1.8.7-p334 :003?> @value = a + b
ruby-1.8.7-p334 :004?> @value
ruby-1.8.7-p334 :005?> end
ruby-1.8.7-p334 :006?> end
=> nil
ruby-1.8.7-p334 :007 > a = A.new
=> #<A:0xb70bd4cc>
ruby-1.8.7-p334 :008 > a[3] = 4
=> 4
ruby-1.8.7-p334 :009 > a
=> #<A:0xb70bd4cc @value=7>

Note that the value of the expression in line 8 is 4 (as shown by IRB)
and not 7, which is the value returned by the method =
If you use the non-syntactic sugar version, though, the return value
is whatever the method returns:

ruby-1.8.7-p334 :010 > a.=(3,4)
=> 7

This is usually not a problem, since for this to bite you, you need to
be doing something in the = and trying to use that return value
outside, not very likely. But anyway, I thought it was worth
mentioning.

Jesus.

···

On Thu, Aug 25, 2011 at 4:57 PM, jack jones <shehio_22@hotmail.com> wrote:

thank you all very much :slight_smile:

16

jack jones wrote in post #1018418:

First of all thank you very much 7stud :slight_smile:
okay I got the method but I had a question how would Ruby know what's in
the and what's out of them
for example :

Well, you could play around with the method and find out.

class Dog
  @array =
  def =(arg1, arg2, arg3)
    array[arg1 + arg2] = arg3 # any operation
  end
end

d = Dog.new
d.abc('hello')
d.[1,2]= 3
# or
d.[1] = 2, 3
# we have 3 args where to put each??

Are you sure you have 3 args?

x = 10, 20, 30
p x

--output:--
[10, 20, 30]

How many 'things' were output for x?

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17

Not sure if you know this, but you can actually still use the approach
with multiple arguments, to avoid "set" and "get" method names. A stupid
example:

class X
  def =(a, b, c)
    p [a, b]
    @a, @b = c, c.reverse
  end

  attr_reader :a, :b
end

x = X.new
x[1, 2] = "foo" #=> [1, 2]; "foo"
p x #=> #<X:0x00000100861f18 @a="foo", @b="oof">
puts x.a #=> foo
puts x.b #=> oof

Live output: http://ideone.com/UxWNS

···

On Mon, Aug 22, 2011 at 3:05 PM, Chuck Remes <cremes.devlist@mac.com> wrote:

Sorry, I didn't read the problem closely enough (too early in the
morning!). You need to pass a ROW and COLUMN to set or get a value in your
matrix instead of just a single value like I posted above.

Something like this might be a good start (untested).

class Matrix
[...]

def set(x, y, value)
   @array[index(x, y)] = value
end

def get(x, y)
   @array[index(x,y)]
end

[...]
end

18

You know operators and functions in C++? In Ruby these two are both
defined in the same way, using def (and, in fact, are the same thing).

-- Matma Rex

19

Jeff Moore wrote in post #1018257:

jack jones wrote in post #1018220:

Thank you very much Chuck Remes :slight_smile:
The problem is I don't understand those functions :
# now name just = ?? The problem is that I don't get the magic
    10 def =(row, column, value) # how does it works?
    11 position = index row, column
    12 @array[position] = value
    13 end
    15 # retrieve value from row, column
    16 def (row, column)
    17 position = index row, column
    18 return @array[position]
    19 end

'=' is actually a method. Does that help?

More precisely, '=' is the name of the method. You can name a method
with three letters, right?

def abc(str)
  puts str
end

This is the same:

def =(str)
  puts str
end

The name of the first method is 'abc', and the name of the second method
is '='. Here is an example:

class Dog
  def abc(str)
    puts str
  end

  def =(str)
    puts str
  end
end

d = Dog.new
d.abc('hello')
d.=('world')

--output:--
hello
world

So in ruby, the = method is just a method with a funny looking name
that is hard to pronounce. However, in the case of = ruby lets you do
some special things; you can call = like this:

d[val1] = val2

and ruby translates that into:

d.=(val1, val2)

Here is a more complete example:

class Dog
  attr_reader :attributes

  def initialize
    @attributes = {}
  end

  def abc(str)
    puts str
  end

  def =(key, val)
    @attributes[key] = val
  end
end

d = Dog.new
d.abc('hello')
d['greeting'] = 'world'

p d.attributes

--output:--
hello
{"greeting"=>"world"}

However, ruby does some tricky things with the second method, so you
can call it like this:

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20

Not quite true. :slight_smile:

class X
  def =(a, b, c, d)
    p [a, b, c, d]
  end
end

x = X.new
x[1, 2, 3] = 4

#=> [1, 2, 3, 4]

···

2011/8/25 Bartosz Dziewoński <matma.rex@gmail.com>

= operator can take either two three arguments