Too Much Matrix: Iterating over Each matrix cell w/o passing the complete thing all the time?

Ruby
1

Okay, where to start?

Sounds like the beginning of a joke, you have a fancy data table, a
splendid output table and a method. You use the method to calculate a
splendid number out of the data table and store it in the output table.
Similar to taking a bean out of the jar and putting it into another
nicer jar.

How do you get the input-data-table value into the method without
passing the whole table as an argument all the time?

The problem is that I iterate the same calculation over all cells, which
is not a problem for four, nine, or 25 cells, but it could be one if
this runs on 100x100 matrices.

This maybe about basic instance/symbol/variable scoping, but I’m not
sure and so far I had avoided dealing with them. So, please, someone
needs to explain me what I actually look for, is there a better way than
passing the complete table into the method?

Thanks in advance,
the Force may be with you—always.

yours James

2

Why are you using indices? All you’re doing with them is referencing the
object inside the matrix, which you already have by using nested “each”
iterators. Use “y” instead of the x & y index and then you won’t have to
pass the matrix around.

3

How do you get the input-data-table value into the method without
passing the whole table as an argument all the time?

I have not checked speed. But, you can try this.

def mc(n)
b = 100
delta = n / ((n**2 + b)**0.5)
end

iv = [[1,2,3],[4,5,6],[7,8,9]]

p iv.map{|a| a.map{|n| mc(n)}}

OR

require ‘matrix’

def mc(n)
b = 100 # smoothing factor
delta = n / ((n**2 + b) ** 0.5)
end

iv = Matrix[[1,2,3],[4,5,6],[7,8,9]]
ot = iv.to_a
iv.each_with_index{|x,r,c| ot[r][c] = mc(x)}
p ot

Harry

4

Subject: Too Much Matrix: Iterating over Each matrix cell w/o passing
the complete thing all the time?
Date: dom 01 set 13 12:07:03 +0200

Quoting James J. ([email protected]):

This maybe about basic instance/symbol/variable scoping, but I’m not
sure and so far I had avoided dealing with them. So, please, someone
needs to explain me what I actually look for, is there a better way than
passing the complete table into the method?

One thing must be clear: when you pass an array (on any other object)
to a function, you do NOT put the whole array onto the stack. The only
thing that is passed is the object reference. Thus, passing a single
integer or a one-billion-element array to a function has the same
(quite small) memory requirements. Thus, if what you are writing is a
quick hack, your solution can cut the cake.

If you are after a cleaner option, one that embodies a bit more Ruby’s
object-oriented spirit, you may create a class that becomes the owner
of your table. Something like this:

class Intricate_calculator
def initialize(table)
@table=table
end

def make_intricate_calculations(at_position_x,at_position_y)
a=@table[at_position_x][at_position_y]
b=100 # smoothing factor
delta=a/((a**2+b)**0.5)
return delta
end
end

This way, you do not need to pass the table to your method each
time. Your example would look like this:

calculator=Intricate_calculator::new([[1,2,3],[4,5,6],[7,8,9]]) # fancy
output_table=Array.new(input_vectors.size){Array.new(input_vectors.size){}}

splendid

output_table.each_with_index do |x,rowindex|
x.each_with_index do |y,colindex|
output_table[rowindex][colindex]=calculator.make_intricate_calculations(rowindex,colindex)
end
end

The important thing to note here is that this solution is certainly
cleaner, but I believe you won’t experience major speed gains.

Carlo

5

Or you could try this with the matrix approach.

require ‘matrix’

def mc(n)
b = 100
delta = n / ((n**2 + b) ** 0.5)
end

iv = Matrix[[1,2,3],[4,5,6],[7,8,9]]
p iv.map{|x| mc(x)}

Harry

6

Nothing wrong with indices where necessary. I was just saying that
passing the indices was unnecessary, given that “y” was the value you
were using inside the method, but you discarded it and passed the
indices instead.

7

I see. Right, you are. «Given» y were the one-only value in universe; so
you cannot had known. How you guys would do it with one table, so I can
do it with many, later, was what I was thinking about. Carlo sensed it
early on. Class#initialize … @table is it, but wasn’t plain to me. I
now read it’s the OO-chapter two, or so, in the Pickaxe? Ouch.

8

«That’s Bingo!»
Or, just «Bingo!»

Solutions within less than ten hours, who can claim to have such a
support? Thx guys.

I’m surprised by the «sheer» number of solutions … I take the
Matrix#map to replace the nested Array#each and may wrap a class around
all, as Carlo had read my minds on the OO spirit.

You guys officially rock.

J.

PS: Joel, what’s wrong about indices, in general?