Convert Array to nested Hash

Dear All,

I’m seeking a method to convert an array like:

[
[“A”, “a”, 1]
[“A”, “b”, 2]
[“B”, “a”, 1]

]

into a hash as follow:
{
{“A” => {“a” => 1, “b” => 2}},
{“B” => {“a” => 1}}
}

Do you have any idea on this? Thanks in advance.

On Oct 24, 2010, at 7:25 AM, Zhi-Qiang L. wrote:

into a hash as follow:
{
{“A” => {“a” => 1, “b” => 2}},
{“B” => {“a” => 1}}
}

Do you have any idea on this? Thanks in advance.

I don’t think that you really want to add 3 layers of dictionary.
If you really want this, then you think about your abstractions to
get a simpler solution.

a = [
[“A”, “a”, 1],
[“A”, “b”, 2],
[“B”, “a”, 1]
]

def a_to_h(a)
h={}
a.map do |nested|
key = nested.shift
h[key] ||= {}
h[key].merge!({ nested.shift => nested.shift })
end
h
end

irb:0> a_to_h(a)
=> {“A”=>{“a”=>1, “b”=>2}, “B”=>{“a”=>1}}

All the best, Sandor Szcs

On Sun, Oct 24, 2010 at 11:27 AM, Sandor Szuecs
[email protected] wrote:

[“B”, “a”, 1]

def a_to_h(a)
=> {“A”=>{“a”=>1, “b”=>2}, “B”=>{“a”=>1}}
Here’s another way:

irb(main):019:0> [
irb(main):020:1* [“A”, “a”, 1],
irb(main):021:1* [“A”, “b”, 2],
irb(main):022:1* [“B”, “a”, 1],
irb(main):023:1*
irb(main):024:1* ].inject({}) do |h,(k1,k2,v)|
irb(main):025:1* (h[k1] ||= {})[k2] = v
irb(main):026:1> h
irb(main):027:1> end
=> {“A”=>{“a”=>1, “b”=>2}, “B”=>{“a”=>1}}

and another one

irb(main):028:0> [
irb(main):029:1* [“A”, “a”, 1],
irb(main):030:1* [“A”, “b”, 2],
irb(main):031:1* [“B”, “a”, 1],
irb(main):032:1*
irb(main):033:1* ].inject(Hash.new {|h,k|
h[k]=Hash.new(&h.default_proc)}) do |h,(k1,k2,v)|
irb(main):034:1* h[k1][k2] = v
irb(main):035:1> h
irb(main):036:1> end
=> {“A”=>{“a”=>1, “b”=>2}, “B”=>{“a”=>1}}

But I totally agree: why build up a strcuture of nested Arrays and
then convert it into the nested Hash structure? Is is much more
efficient to build up the Hash structure initially. One might even
create a Struct for values in the top level Hash.

Cheers

robert

On Oct 24, 2010, at 7:07 PM, Robert K. wrote:

  ["A", "a", 1]

]

irb(main):024:1* ].inject({}) do |h,(k1,k2,v)|
irb(main):031:1* [“B”, “a”, 1],
efficient to build up the Hash structure initially. One might even
create a Struct for values in the top level Hash.

Cheers

robert


remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

A beautiful injecting, thank you all. Because an external library return
the array, I have to do this.

A beautiful injecting

The first solution given is by far the more readable and more
understandable, compared to the injects, I find.

On Oct 25, 2010, at 12:02 AM, Adam P. wrote:

A beautiful injecting

The first solution given is by far the more readable and more
understandable, compared to the injects, I find.

I agree.

On Oct 24, 6:07am, Robert K. [email protected] wrote:

=> {“A”=>{“a”=>1, “b”=>2}, “B”=>{“a”=>1}}
irb(main):034:1* h[k1][k2] = v
irb(main):035:1> h
irb(main):036:1> end
=> {“A”=>{“a”=>1, “b”=>2}, “B”=>{“a”=>1}}

a = [ [“A”, “a”, 1],
[“A”, “b”, 2],
[“B”, “a”, 1] ]
h = Hash.new{|hash,key| hash[key] = {} }
a.each{|x,y,z| h[x][y] = z}

On Oct 24, 2010, at 7:07 PM, Robert K. wrote:

  ["A", "a", 1]

]

irb(main):024:1* ].inject({}) do |h,(k1,k2,v)|
irb(main):031:1* [“B”, “a”, 1],
efficient to build up the Hash structure initially. One might even
create a Struct for values in the top level Hash.

Cheers

robert


remember.guy do |as, often| as.you_can - without end
http://blog.rubybestpractices.com/

I’m sorry to bring this old topic out. But there is a question make me
confused.

irb(main):019:0> [
irb(main):020:1* [“A”, “a”, 1],
irb(main):021:1* [“A”, “b”, 2],
irb(main):022:1* [“B”, “a”, 1],
irb(main):023:1*
irb(main):024:1* ].inject({}) do |h,(k1,k2,v)|
irb(main):025:1* (h[k1] ||= {})[k2] = v
irb(main):026:1> h
irb(main):027:1> end
=> {“A”=>{“a”=>1, “b”=>2}, “B”=>{“a”=>1}}

Is the tuple (k1, k2, v) in block arguments an array? What’s the meaning
of () in block arguments? Thanks.

Best regards,
Zhi-Qiang L.
[email protected]

On Nov 5, 2010, at 10:58 AM, Zhi-Qiang L. wrote:

 ["A", "b", 2]

Do you have any idea on this? Thanks in advance.

irb:0> a_to_h(a)
irb(main):025:1* (h[k1] ||= {})[k2] = v
irb(main):032:1*
create a Struct for values in the top level Hash.

irb(main):026:1> h
irb(main):027:1> end
=> {“A”=>{“a”=>1, “b”=>2}, “B”=>{“a”=>1}}

Is the tuple (k1, k2, v) in block arguments an array? What’s the
meaning of () in block arguments? Thanks.

Best regards,
Zhi-Qiang L.
[email protected]

The inject() will pass two arguments to the block. The accumulated
value and the new element. In the use of the parentheses in the block
arguments acts like an array assignment so the individual values of
the array element are available with more meaningful names.

.inject({}) do |h,array|
k1, k2, v = array
(h[k1] ||= {})[k2] = v
h
end

is the same thing without using the block’s ability to “unpack” the
array elements.

-Rob

Rob B.
[email protected] http://AgileConsultingLLC.com/
[email protected] http://GaslightSoftware.com/

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