Hashed matrix


#1

Hello, I’d like to use a specific matrix with string as key for lines
and integer index for columns. I could also use string for columns (a
string version of integer), it doesn’t matter. I use the matrix to store
a small object (named State) I just need to access data like that :
matrix[a_string][a_number]

Here is how I tried to do it :
matrix = Hash.new{ |hash, key| hash[key] = Array.new(5, State.new(0,
“”)) }

But I have strange values, is there a better way to make that matrix ?


#2

2009/4/20 Yoann M. removed_email_address@domain.invalid:

Hello, I’d like to use a specific matrix with string as key for lines
and integer index for columns. I could also use string for columns (a
string version of integer), it doesn’t matter. I use the matrix to store
a small object (named State) I just need to access data like that :
matrix[a_string][a_number]

Here is how I tried to do it :
matrix = Hash.new{ |hash, key| hash[key] = Array.new(5, State.new(0,
“”)) }

You want the block form of Array.new because otherwise all array
entries point to the same object:

matrix = Hash.new{ |hash, key| hash[key] = Array.new(5) {
State.new(0,"") } }

Alternative approach: use an Array of String and Fixnum as Hash key:

class Matrix
def initialize
@hash = Hash.new {|h,k| h[k] = State.new(0, “”)}
end

def
@hash[[row, col]]
end

def []=(row,col, val)
raise ArgumentError, “Not a state %p” % val
@hash[[row, col]] = val
end
end

This is likely more efficient if your matrices are large and sparse.

Kind regards

robert


#3

2009/4/20 Robert K. removed_email_address@domain.invalid:

end

def
@hash[[row, col]]
end

def []=(row,col, val)
raise ArgumentError, “Not a state %p” % val

This should have read

raise ArgumentError, “Not a state %p” % val unless State === val


#4

Thanks for your answer, you’re right I had the same object in my array,
this is why I had strange values.
I use a really small matrix so it’s not a big deal to be efficient, I’ll
use your first idea.

Thank you.