sparse multi-dimensional arrays

[Bill Birkett]

I did like to convert some programs I wrote in Perl to Ruby. I'm
working with sparse three dimensional data. Here's an example in
Perl. The array @a has just two elements. The rest are undefined.

#!/usr/bin/perl -w

$a[0][0][0] = 0;
$a[100][100][100] = 100;

print "$a[0][0][0]\n";
print "$a[100][100][100]\n";

The output:

0
100

Is there an easy way to implement this sort of data structure in
Ruby? The Array class seems limited to one dimension. I looked at the
Matrix class, but there doesn't appear to be any way of assigning
values to the individual matrix elements (which seems pretty strange,
so maybe I'm overlooking the obvious).

-Bill
--

William B. Birkett - <[email protected]>
Print Quality Consultant
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[Logan Capaldo]

I did like to convert some programs I wrote in Perl to Ruby. I'm
working with sparse three dimensional data. Here's an example in
Perl. The array @a has just two elements. The rest are undefined.

#!/usr/bin/perl -w

$a[0][0][0] = 0;
$a[100][100][100] = 100;

print "$a[0][0][0]\n";
print "$a[100][100][100]\n";

The output:

0
100

Is there an easy way to implement this sort of data structure in
Ruby? The Array class seems limited to one dimension. I looked at the
Matrix class, but there doesn't appear to be any way of assigning
values to the individual matrix elements (which seems pretty strange,
so maybe I'm overlooking the obvious).

It's pretty easy if you know the dimensions before hand, a bit more
hackery pokery if you don't.
a = Array.new(101) { Array.new(101) { Array.new(101) } }
a[0][0][0] = 0
a[100][100][100] = 100

puts a[0][0][0]
puts a[100][100][100]

 

[Nathan Grant]

$a[0][0][0] = 0;

$a[100][100][100] = 100;

print "$a[0][0][0]\n";
print "$a[100][100][100]\n";

The output:

0
100

I saw this on inquirylabs.com recently [1]

hsh = Hash.new(&(p=lambda{|h,k| h[k] = Hash.new(&p)}))

hsh[0][0][0] = 0 >> 0
hsh[100][100][100] = 100 >> 100

HTH

Nathan

[1]
http://blog.inquirylabs.com/2006/09/20/ruby-hashes-of-arbitrary-depth/

 

[Jason Nordwick]

Close:

a={}
a[[0,0,0]], a[[100,100,100]] = 0, 100
puts "#{a[[0,0,0]]}"
puts "#{a[[100,100,100]]}"

But you might like this better (my Ruby isn't very good, so please excuse me if I overcomplicate these definitions):

class SparseMatrix < Hash
alias ldget :[]
alias ldset :[]=
def[](*i); self.oldget(i); end
def[]=(*i); v=i.pop; self.oldset(i,v); end
end

a = SparseMatrix.new
a[0,0,0], a[100,100,100] = 0, 100


irb(main):017:0> a
=> {[0, 0, 0]=>0, [100, 100, 100]=>100}
irb(main):018:0> puts "#{a[0,0,0]}"
0
=> nil
irb(main):019:0> puts "#{a[100,100,100]}"
100
=> nil
irb(main):020:0> puts "#{a[2,2,2]}"

=> nil
irb(main):021:0>

-j

 

[Jason Nordwick]

irb(main):005:0> hsh[1]
=> {}
irb(main):006:0> hsh[2]
=> {}
irb(main):007:0> hsh[3]
=> {}
irb(main):008:0> hsh
=> {1=>{}, 2=>{}, 3=>{}}

ugh.

-j

$a[0][0][0] = 0;
$a[100][100][100] = 100;

print "$a[0][0][0]\n";
print "$a[100][100][100]\n";

The output:

0
100

I saw this on inquirylabs.com recently [1]

hsh = Hash.new(&(p=lambda{|h,k| h[k] = Hash.new(&p)}))

hsh[0][0][0] = 0 >> 0
hsh[100][100][100] = 100 >> 100

HTH

Nathan

[1]
http://blog.inquirylabs.com/2006/09/20/ruby-hashes-of-arbitrary-depth/