# Question about multi-demension hash initialization

**URL:** <https://www.ruby-forum.com/t/question-about-multi-demension-hash-initialization/149051>\
**Category:** Ruby\
**Created:** [September 19, 2008, 8:30pm UTC](https://www.ruby-forum.com/t/question-about-multi-demension-hash-initialization/149051 "2008-09-19T20:30:06Z")\
**Posts on this page:** 5\
**Page:** 1

<div class="post-metadata">

**Author:** ![rubina](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e47c2d/32.png) [@rubina](https://www.ruby-forum.com/u/rubina)\
**Post date:** [September 19, 2008, 8:30pm UTC](https://www.ruby-forum.com/t/question-about-multi-demension-hash-initialization/149051/1 "2008-09-19T20:30:06Z")

</div>

Team,  
Is there a quick (perhaps one liner) way to initialize the following  
hashes  
into just one hash?

def xwing(ia)

p ia

puts " "  
p @xwing

r1 = {“1” =\> 0, “2” =\> 0, “3” =\> 0, “4” =\> 0, “5” =\> 0, “6” =\> 0, “7”  
=\>  
0, “8” =\> 0, “9” =\> 0}  
r2 = {“1” =\> 0, “2” =\> 0, “3” =\> 0, “4” =\> 0, “5” =\> 0, “6” =\> 0, “7”  
=\>  
0, “8” =\> 0, “9” =\> 0}  
r3 = {“1” =\> 0, “2” =\> 0, “3” =\> 0, “4” =\> 0, “5” =\> 0, “6” =\> 0, “7”  
=\>  
0, “8” =\> 0, “9” =\> 0}  
r4 = {“1” =\> 0, “2” =\> 0, “3” =\> 0, “4” =\> 0, “5” =\> 0, “6” =\> 0, “7”  
=\>  
0, “8” =\> 0, “9” =\> 0}  
r5 = {“1” =\> 0, “2” =\> 0, “3” =\> 0, “4” =\> 0, “5” =\> 0, “6” =\> 0, “7”  
=\>  
0, “8” =\> 0, “9” =\> 0}  
r6 = {“1” =\> 0, “2” =\> 0, “3” =\> 0, “4” =\> 0, “5” =\> 0, “6” =\> 0, “7”  
=\>  
0, “8” =\> 0, “9” =\> 0}  
r7 = {“1” =\> 0, “2” =\> 0, “3” =\> 0, “4” =\> 0, “5” =\> 0, “6” =\> 0, “7”  
=\>  
0, “8” =\> 0, “9” =\> 0}  
r8 = {“1” =\> 0, “2” =\> 0, “3” =\> 0, “4” =\> 0, “5” =\> 0, “6” =\> 0, “7”  
=\>  
0, “8” =\> 0, “9” =\> 0}  
r9 = {“1” =\> 0, “2” =\> 0, “3” =\> 0, “4” =\> 0, “5” =\> 0, “6” =\> 0, “7”  
=\>  
0, “8” =\> 0, “9” =\> 0}

end

(0…8).each do |r|  
xwing(@xwing[[r][0]]) # @xwing is defined previously  
end

Actually, I wanted just one hash, @frequency, but I did not know how to  
do  
it.

Thank you

Ruby student

---

<div class="post-metadata">

**Author:** ![rubina](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e47c2d/32.png) [@rubina](https://www.ruby-forum.com/u/rubina)\
**Post date:** [September 20, 2008, 4:55pm UTC](https://www.ruby-forum.com/t/question-about-multi-demension-hash-initialization/149051/2 "2008-09-20T16:55:30Z")

</div>

On 19.09.2008 20:21, Ruby S. wrote:

> puts " "  
> r5 = {“1” =\> 0, “2” =\> 0, “3” =\> 0, “4” =\> 0, “5” =\> 0, “6” =\> 0, “7” =\>  
> end
> 
> (0…8).each do |r|  
> xwing(@xwing[[r][0]]) # @xwing is defined previously  
> end
> 
> Actually, I wanted just one hash, @frequency, but I did not know how to do  
> it.

Err, what? You know how to create nine hashes but you do not know how  
to create one? I’m suspecting that there is something missing from your  
posting.

Maybe you wanted something like this:

irb(main):004:0\> require ‘pp’  
=\> true  
irb(main):005:0\> pp Array.new(9) { Hash[\*(1…9).map  
{|i|[i.to\_s,0]}.flatten] }  
[{“6”=\>0, “7”=\>0, “8”=\>0, “9”=\>0, “1”=\>0, “2”=\>0, “3”=\>0, “4”=\>0,  
“5”=\>0},  
{“6”=\>0, “7”=\>0, “8”=\>0, “9”=\>0, “1”=\>0, “2”=\>0, “3”=\>0, “4”=\>0,  
“5”=\>0},  
{“6”=\>0, “7”=\>0, “8”=\>0, “9”=\>0, “1”=\>0, “2”=\>0, “3”=\>0, “4”=\>0,  
“5”=\>0},  
{“6”=\>0, “7”=\>0, “8”=\>0, “9”=\>0, “1”=\>0, “2”=\>0, “3”=\>0, “4”=\>0,  
“5”=\>0},  
{“6”=\>0, “7”=\>0, “8”=\>0, “9”=\>0, “1”=\>0, “2”=\>0, “3”=\>0, “4”=\>0,  
“5”=\>0},  
{“6”=\>0, “7”=\>0, “8”=\>0, “9”=\>0, “1”=\>0, “2”=\>0, “3”=\>0, “4”=\>0,  
“5”=\>0},  
{“6”=\>0, “7”=\>0, “8”=\>0, “9”=\>0, “1”=\>0, “2”=\>0, “3”=\>0, “4”=\>0,  
“5”=\>0},  
{“6”=\>0, “7”=\>0, “8”=\>0, “9”=\>0, “1”=\>0, “2”=\>0, “3”=\>0, “4”=\>0,  
“5”=\>0},  
{“6”=\>0, “7”=\>0, “8”=\>0, “9”=\>0, “1”=\>0, “2”=\>0, “3”=\>0, “4”=\>0,  
“5”=\>0}]  
=\> nil  
irb(main):006:0\>

However, given the structure of your Hashes I wonder why you do not want  
to use Arrays instead. E.g.

irb(main):001:0\> pp Array.new(9) { Array.new(9, 0) }  
[[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0]]  
=\> nil

Or even use a Matrix.

irb(main):006:0\> require ‘matrix’  
=\> true  
irb(main):007:0\> pp Matrix.zero 9  
Matrix[[0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0,  
0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0  
], [0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0], [0, 0, 0,  
0, 0, 0, 0, 0, 0], [0, 0, 0, 0, 0, 0, 0, 0, 0], [  
0, 0, 0, 0, 0, 0, 0, 0, 0]]  
=\> nil  
irb(main):008:0\> pp Matrix.zero(9).to\_a  
[[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0],  
[0, 0, 0, 0, 0, 0, 0, 0, 0]]  
=\> nil  
irb(main):009:0\>

Kind regards

robert

---

<div class="post-metadata">

**Author:** ![rubina](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e47c2d/32.png) [@rubina](https://www.ruby-forum.com/u/rubina)\
**Post date:** [September 20, 2008, 10:16pm UTC](https://www.ruby-forum.com/t/question-about-multi-demension-hash-initialization/149051/3 "2008-09-20T22:16:55Z")

</div>

On Sat, Sep 20, 2008 at 10:47 AM, Robert K.  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote:

> > def xwing(ia)  
> > r3 = {“1” =\> 0, “2” =\> 0, “3” =\> 0, “4” =\> 0, “5” =\> 0, “6” =\> 0, “7” =\>  
> > 0, “8” =\> 0, “9” =\> 0}
> 
> irb(main):004:0\> require ‘pp’  
> {“6”=\>0, “7”=\>0, “8”=\>0, “9”=\>0, “1”=\>0, “2”=\>0, “3”=\>0, “4”=\>0, “5”=\>0},  
> [0, 0, 0, 0, 0, 0, 0, 0, 0],  
> irb(main):006:0\> require ‘matrix’  
> [0, 0, 0, 0, 0, 0, 0, 0, 0],  
> Kind regards
> 
> ```
> robert
> 
> ```
> 
> Robert,  
> First, thank you for your help and sample code.

What I need to do is to pass an integer compose of minimum 2 digits and  
maximum of 8 and count the how many time a digit appears.  
For example, I have a multidimensional array (9x9), which I then take  
each  
row and each column at a time.

For instance, the following are two rows extracted from the 9x9 array:

r1 = [345, 8, 459, 125679, 123, 45679, 379, 679, 79]  
r8 = [9, 4, 6789, 356, 1, 357, 2356, 257, 67]

So, for row r1:  
1s = 2, 2s = 2, 3s = 3, 4s = 3, 5s = 4, 6s = 3, 7s = 5, 8s = 1, 9s = 6

The same reasoning follows for r8.  
So the 9x9 hash represents the 9x9 array for Sudoku, but instead of  
representing a Sudoku element, the key = the number while the value is  
the  
count (frequency) of that key.  
I am not sure if I am explaining myself clearly.

I need this information in order to successfully implement one of the  
Sudoku  
rules, the so called x-wing rule, which explanation can be found at:  
[http://www.sudokuoftheday.com/pages/techniques-8.php](http://www.sudokuoftheday.com/pages/techniques-8.php)

I can find my way around with arrays, but with hashes I am not familiar  
at  
all.

Again, thank you for your help.

Ruby S.

---

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**Author:** ![rubina](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e47c2d/32.png) [@rubina](https://www.ruby-forum.com/u/rubina)\
**Post date:** [September 21, 2008, 10:56am UTC](https://www.ruby-forum.com/t/question-about-multi-demension-hash-initialization/149051/4 "2008-09-21T10:56:13Z")

</div>

On 20.09.2008 21:30, Ruby S. wrote:

> On Sat, Sep 20, 2008 at 10:47 AM, Robert K.  
> [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote:
> 
> > On 19.09.2008 20:21, Ruby S. wrote:  
> > First, thank you for your help and sample code.

You’re welcome.

> What I need to do is to pass an integer compose of minimum 2 digits and  
> maximum of 8 and count the how many time a digit appears.

That’s easy.

irb(main):006:0\> i = rand 100000000  
=\> 3976173  
irb(main):007:0\> h = Hash.new 0  
=\> {}  
irb(main):008:0\> i.to\_s(10).scan(/\d/) {|dg| h[dg] += 1}  
=\> “3976173”  
irb(main):009:0\> h  
=\> {“6”=\>1, “7”=\>2, “9”=\>1, “1”=\>1, “3”=\>2}  
irb(main):010:0\>

> For example, I have a multidimensional array (9x9), which I then take each  
> row and each column at a time.

This is a _two_ dimensional Array.

> representing a Sudoku element, the key = the number while the value is the  
> count (frequency) of that key.  
> I am not sure if I am explaining myself clearly.

Me, too. 😉 Given the fact that you are dealing with Sudoku it is a  
complete mystery to me why you want to count “digits”. It seems, a  
Sudoku can have _numbers_ in all locations and you want to make sure  
that no number appears twice in a row and in a column. Basically there  
are many ways to do this, one would be a bit set (you can use an integer  
for that, see at end).

> I need this information in order to successfully implement one of the Sudoku  
> rules, the so called x-wing rule, which explanation can be found at:  
> [http://www.sudokuoftheday.com/pages/techniques-8.php](http://www.sudokuoftheday.com/pages/techniques-8.php)
> 
> I can find my way around with arrays, but with hashes I am not familiar at  
> all.

Since you are indexing by number (or more precisely: digit) anyway what  
do you gain by using a Hash?

Cheers

robert

A half baked example to illustrate what I mean with the bit set check:

#!/bin/env ruby

require ‘pp’

class Sudoku  
def initialize(size)  
raise ArgumentError unless 2 \<= size  
@size = size  
@dat = Array.new(size \* size)  
@rows = Array.new(size, 0)  
@cols = Array.new(size, 0)  
end

def   
@dat[pos(x,y)]  
end

def []=(x,y,v)  
raise “Not allowed” if @rows[x][v] == 1 || @cols[y][v] == 1  
@dat[pos(x,y)] = v  
@rows[x] |= 1 \<\< v  
@cols[y] |= 1 \<\< v  
end

def to\_s  
s = “”  
@size.times do |i|  
s \<\< “[” \<\< @dat[i \* @size, @size].join(", ") \<\< “]\n”  
end  
s  
end

private  
def pos(x,y)  
raise ArgumentError unless [x,y].all? {|a| Integer === a}  
x \* @size + y  
end  
end

s = Sudoku.new 9

s[2,0] = 1  
puts s

s[1,0] = 1

---

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**Author:** ![rubina](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/r/e47c2d/32.png) [@rubina](https://www.ruby-forum.com/u/rubina)\
**Post date:** [September 21, 2008, 1:05pm UTC](https://www.ruby-forum.com/t/question-about-multi-demension-hash-initialization/149051/5 "2008-09-21T13:05:39Z")

</div>

On Sun, Sep 21, 2008 at 4:47 AM, Robert K.  
[removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid)wrote:

> You’re welcome.  
> =\> {}  
> This is a _two_ dimensional Array.
> 
> > So the 9x9 hash represents the 9x9 array for Sudoku, but instead of
> 
> you gain by using a Hash?  
> require ‘pp’  
> def   
> def to\_s  
> x \* @size + y  
> Robert,  
> Again, thanks a bunch.  
> You have given me enough material for a good few days to digest.  
> I’ll play and learn from your sample code.

Thanks again,

Ruby S.