Odd hash behaviour
Kev Jackson
I'm still munging data and I'm struggling with Ruby's hash
For example, I want to store a value with an associated key (sounds like
a hash or associated array), but I don't want duplicates (more like a
set, in Java I'd use a HashSet to get this behaviour).
@min_pks = Hash.new()
...
# store value for key unless we already have it
@min_pks[min_key] = no unless @min_pks.has_key?(min_key)
Regardless of how I structure the above, the Hash always stores every
value, it's as if the Hash always returns a false to the query has_key?,
so it always stores a new value
The key I'm using is a 3 letter abbreviation like 'MID', 'MCY' etc, and
in the incoming data they are duplicated
I've tried googling, I've tried ri etc, and there doesn't seem to be a
Set class with Ruby (I'd rather not write my own), at least according to
the docs. I'm also aware that the problem is between the keyboard and
the chair, it's not Ruby's falut, I'm doing something dim.
Anyone help me out?
Kev
Jeremy Tregunna
On 3-Oct-05, at 11:56 PM, Kev Jackson wrote:
> Hi all,
>
> I'm still munging data and I'm struggling with Ruby's hash
>
> For example, I want to store a value with an associated key (sounds
> like a hash or associated array), but I don't want duplicates (more
> like a set, in Java I'd use a HashSet to get this behaviour).
>
> @min_pks = Hash.new()
> ....
> # store value for key unless we already have it
> @min_pks[min_key] = no unless @min_pks.has_key?(min_key)
>
> Regardless of how I structure the above, the Hash always stores every
> value, it's as if the Hash always returns a false to the query
> has_key?, so it always stores a new value
As a Hash should. Keep in mind, that if you have a key 'foo' in your
hash (let's say: @min_pks['foo'] => 42) and later you set 'foo' again
(@min_pks['foo'] = 16) then @min_pks['foo'] is now 16, and the previous
42 value is gone (read: overwrote the previous value).
> The key I'm using is a 3 letter abbreviation like 'MID', 'MCY' etc,
> and in the incoming data they are duplicated
>
> I've tried googling, I've tried ri etc, and there doesn't seem to be a
> Set class with Ruby (I'd rather not write my own), at least according
> to the docs. I'm also aware that the problem is between the keyboard
> and the chair, it's not Ruby's falut, I'm doing something dim.
Ruby comes with a Set class; you just need to require it first.
Consider:
require 'set'
your_set = Set.new ['foo', 42]
> Kev
--
Jeremy Tregunna
jtre...@blurgle.ca
"If debugging is the process of removing bugs, then programming must be
the process of putting them in." --Dykstra
Vance A Heron
Seems to work for me ...
$ irb
irb(main):001:0> @min_pks = Hash.new()
=> {}
irb(main):002:0> key = 'MID'
=> "MID"
irb(main):003:0> @min_pks[key] = 1 unless @min_pks.has_key?(key)
=> 1
irb(main):004:0> @min_pks[key] = 2 unless @min_pks.has_key?(key)
=> nil
irb(main):005:0> p @min_pks
{"MID"=>1}
=> nil
Could you give the rest of your code and possibly some sample
data?
Vance
On Tue, 2005-10-04 at 12:56 +0900, Kev Jackson wrote:
> Hi all,
>
> I'm still munging data and I'm struggling with Ruby's hash
>
> For example, I want to store a value with an associated key (sounds like
> a hash or associated array), but I don't want duplicates (more like a
> set, in Java I'd use a HashSet to get this behaviour).
>
> @min_pks = Hash.new()
> ....
Kev Jackson
>Kev,
>Seems to work for me ...
>$ irb
>irb(main):001:0> @min_pks = Hash.new()
>=> {}
>irb(main):002:0> key = 'MID'
>=> "MID"
>irb(main):003:0> @min_pks[key] = 1 unless @min_pks.has_key?(key)
>=> 1
>irb(main):004:0> @min_pks[key] = 2 unless @min_pks.has_key?(key)
>=> nil
>irb(main):005:0> p @min_pks
>{"MID"=>1}
>=> nil
>
>Could you give the rest of your code and possibly some sample
>data?
>
>
Actually it was working, but when printing out the values, it prints
everything (ie including things that shouldn't have been in the Hash).
I figured it all out in the end, my logic was a little twisted and the
print was always executing (hence my confusion), the Hash was behaving
perfectly.
As for the Set using
require 'Set'
That's the problem with not having docs for 1.8.2, the only docs I have
cover 1.6 (and not too much of that). Suppose I'll have to get Pickaxe 2 :)
Kev
Ryan Leavengood
>
> That's the problem with not having docs for 1.8.2, the only docs I have
> cover 1.6 (and not too much of that). Suppose I'll have to get Pickaxe 2 :)
Don't forget ri:
C:\Documents and Settings\rjl>ri Set
------------------------------------------------------------- Class: Set
Set implements a collection of unordered values with no duplicates.
This is a hybrid of Array's intuitive inter-operation facilities
and Hash's fast lookup.
Several methods accept any Enumerable object (implementing +each+)
for greater flexibility: new, replace, merge, subtract, |, &, -, ^.
..
[rest elided]
"ri -c" will also list all the classes ri knows about, in case you
aren't sure what you are looking for.
Ryan
James Edward Gray II
> On 10/4/05, Kev Jackson <kevin....@it.fts-vn.com> wrote:
>
>>
>> That's the problem with not having docs for 1.8.2, the only docs I
>> have
>> cover 1.6 (and not too much of that). Suppose I'll have to get
>> Pickaxe 2 :)
>>
>
> Don't forget ri:
James Edward Gray II
Gavin Kistner
>>> That's the problem with not having docs for 1.8.2, the only docs
>>> I have
>>> cover 1.6 (and not too much of that). Suppose I'll have to get
>>> Pickaxe 2 :)
In case you've been to ruby-doc and were confused, use the "Core API"
and "Std Lib" links at the top to get started.