Dynamically creating a multi dimensional hash

ruby-talk
1

Hello,

I am trying to do something that on the surface seems easy, but in
practice I don't have a clue how to approach it. I need to create a
multi-dimensional hash to represent certain attributes of a particular
item. When I hardcode the hash for testing purposes it looks something
like this:

@skuList = [{:sku => "XXXX", :price => "$ZZZZ.ZZ"}, {:sku => "YYYY",
:price => "$AAA.AA"}]

However, in production I need to be able to generate an almost exact
same hash dynamically, with the exception of that I don't know how many
objects will need to be inserted into the hash.

Basically, I will be reading in a file that contains an unknown number
of item names and need to return hash that contains the above
attributes for all entries in the file that I just read.

Unfortunately, I am very new to Ruby, and don't have a clue where to
start on something like this.

Can someone help me out?

Thanks,
David

···

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2

I am trying to do something that on the surface seems easy, but in
practice I don't have a clue how to approach it. I need to create a
multi-dimensional hash to represent certain attributes of a particular
item. When I hardcode the hash for testing purposes it looks something
like this:

@skuList = [{:sku => "XXXX", :price => "$ZZZZ.ZZ"}, {:sku => "YYYY",
:price => "$AAA.AA"}]

First of all @skuList is not a Hash but an Array.

However, in production I need to be able to generate an almost exact
same hash dynamically, with the exception of that I don't know how many
objects will need to be inserted into the hash.

Is the number of objects unknown or the level of nesting?

Basically, I will be reading in a file that contains an unknown number
of item names and need to return hash that contains the above
attributes for all entries in the file that I just read.

Ok, you do not need arbitrary nesting but rather you want to add a variable number of items to the Array.

Unfortunately, I am very new to Ruby, and don't have a clue where to
start on something like this.

You should have a look at the documentation of class Array. You'll find methods for changing an Array's content there.

Btw, a few other remarks:

In Ruby we conventionally use identifiers like @sku_list instead of @skuList which you rather find in Java. While of course you are free to choose it may make your code easier readable for your fellow Ruby programmers if you go with that convention.

If your set of attributes is fixed as seems to be the case it is a good idea to use a class for this instead of Hash instances. The easiest would be

SkuItem = Struct.new :sku, :price

Kind regards

  robert

···

On 11.08.2009 21:45, David Sainte-claire wrote:

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

3

David Sainte-claire wrote:

Hello,

I am trying to do something that on the surface seems easy, but in
practice I don't have a clue how to approach it. I need to create a
multi-dimensional hash to represent certain attributes of a particular
item. When I hardcode the hash for testing purposes it looks something
like this:

@skuList = [{:sku => "XXXX", :price => "$ZZZZ.ZZ"}, {:sku => "YYYY",
:price => "$AAA.AA"}]

However, in production I need to be able to generate an almost exact
same hash dynamically, with the exception of that I don't know how many
objects will need to be inserted into the hash.

Basically, I will be reading in a file that contains an unknown number
of item names and need to return hash that contains the above
attributes for all entries in the file that I just read.

Unfortunately, I am very new to Ruby, and don't have a clue where to
start on something like this.

Can someone help me out?

Thanks,
David

Looks like an array of hashes. What do you mean by "multidimensional hash"?

There's a ruby idiom that may or may not apply here, making use of the default proc of a hash to create arbitrary nesting:

make_hash = proc do |hash,key|
   hash[key] = Hash.new(&make_hash)
end

h = Hash.new(&make_hash)

h[1][2][3] = "foo"

p h # => {1=>{2=>{3=>"foo"}}}

But if you are just trying to construct an array of hashes, something like this may work:

ary =
File.open(...).each do |line|
   hash = your_parser(line)
   ary << hash
end

Sorry if I've misunderstood!

···

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       vjoel : Joel VanderWerf : path berkeley edu : 510 665 3407