Hi all,
I'm trying to loop across a dataset and create a hash where each value is an array so that later I can loop over the hash and for each key (it's important I store the key), I can loop over the array contained and spit out some results.
Without looking at the docs I wanted to do something like...
(in pseudo-code)
loop across data here
work_types[nsc_id]=do |types|
types << data[7]
end
end loop
where work_types is the hash and types is the array I want to accumulate data in
This doesn't work, so I'm wondering what the ruby idiom for this kind of thing would be. Essentially for each piece of data I want to get the appropriate value from the Hash and append the value on to the end of the array associated with the key, or if it doesn't exist in the Hash, create a new entry with a new array populated with the value.
I'm sure there's a very simple way of doing this, but I can't see the method I want in the standard library docs - I thought it might be collect, but it doesn't look like it
Thanks
Kev
i think you want something like this:
harp:~ > irb
irb(main):001:0> work_types = Hash::new{|h,k| h[k] = }
=> {}
irb(main):002:0> work_types[ 'foo' ] << 42
=> [42]
irb(main):003:0> work_types[ 'foo' ] << 42
=> [42, 42]
irb(main):004:0> work_types[ 'bar' ] << 'forty-two'
=> ["forty-two"]
irb(main):005:0> work_types
=> {"foo"=>[42, 42], "bar"=>["forty-two"]}
if not you'll have to post more about your exact problem and some sample data.
hth.
-a
···
On Wed, 12 Oct 2005, Kev Jackson wrote:
Hi all,
I'm trying to loop across a dataset and create a hash where each value is an array so that later I can loop over the hash and for each key (it's important I store the key), I can loop over the array contained and spit out some results.
Without looking at the docs I wanted to do something like...
(in pseudo-code)
loop across data here
work_types[nsc_id]=do |types|
types << data[7]
end
end loop
where work_types is the hash and types is the array I want to accumulate data in
This doesn't work, so I'm wondering what the ruby idiom for this kind of thing would be. Essentially for each piece of data I want to get the appropriate value from the Hash and append the value on to the end of the array associated with the key, or if it doesn't exist in the Hash, create a new entry with a new array populated with the value.
I'm sure there's a very simple way of doing this, but I can't see the method I want in the standard library docs - I thought it might be collect, but it doesn't look like it
Thanks
Kev
--
email :: ara [dot] t [dot] howard [at] noaa [dot] gov
phone :: 303.497.6469
Your life dwells amoung the causes of death
Like a lamp standing in a strong breeze. --Nagarjuna
===============================================================================
Ara.T.Howard wrote:
Hi all,
I'm trying to loop across a dataset and create a hash where each value is an array so that later I can loop over the hash and for each key (it's important I store the key), I can loop over the array contained and spit out some results.
Without looking at the docs I wanted to do something like...
(in pseudo-code)
loop across data here
work_types[nsc_id]=do |types|
types << data[7]
end
end loop
where work_types is the hash and types is the array I want to accumulate data in
This doesn't work, so I'm wondering what the ruby idiom for this kind of thing would be. Essentially for each piece of data I want to get the appropriate value from the Hash and append the value on to the end of the array associated with the key, or if it doesn't exist in the Hash, create a new entry with a new array populated with the value.
I'm sure there's a very simple way of doing this, but I can't see the method I want in the standard library docs - I thought it might be collect, but it doesn't look like it
Thanks
Kev
i think you want something like this:
harp:~ > irb
irb(main):001:0> work_types = Hash::new{|h,k| h[k] = }
=> {}
irb(main):002:0> work_types[ 'foo' ] << 42
=> [42]
irb(main):003:0> work_types[ 'foo' ] << 42
=> [42, 42]
irb(main):004:0> work_types[ 'bar' ] << 'forty-two'
=> ["forty-two"]
irb(main):005:0> work_types
=> {"foo"=>[42, 42], "bar"=>["forty-two"]}
if not you'll have to post more about your exact problem and some sample data.
hth.
-a
I got the output I wanted with this
work_types = Hash.new
if work_types.has_key?(nsc_id) then
work_types[nsc_id]= work_types[nsc_id].include?(work_type) ? work_types[nsc_id] : work_types[nsc_id] << work_type
else
work_types[nsc_id]= [work_type]
end
So the problem is solved, but I wonder if there's a more elegant way of doing it (especially the check to see if the value is already in the array). My first assumption was that assignment to a Hash took a block (hence the pseudo code), I was actually a little suprised that it didn't 
Kev
···
On Wed, 12 Oct 2005, Kev Jackson wrote:
Kev Jackson:
loop across data here
work_types[nsc_id]=do |types|
types << data[7]
end
end loop
where work_types is the hash and types is the array I want to accumulate
data in
...
I got the output I wanted with this
work_types = Hash.new
if work_types.has_key?(nsc_id) then
work_types[nsc_id]= work_types[nsc_id].include?(work_type) ?
work_types[nsc_id] : work_types[nsc_id] << work_type
else
work_types[nsc_id]= [work_type]
end
So the problem is solved, but I wonder if there's a more elegant way of
doing it (especially the check to see if the value is already in the
array). My first assumption was that assignment to a Hash took a block
(hence the pseudo code), I was actually a little suprised that it didn't
How about this?
work_types = Hash.new {|h, k| h[k] = }
work_types[nsc_id] << work_type unless
work_types[nsc_id].include?(work_type)
Cheers,
Dave
this is one easy way
work_types = Hash::new{|h,k| h[k] = }
work_types[ nsc_id ].push( work_type ).uniq!
but does a bit of extra work. another way would be to use set
require 'set'
work_types = Hash::new{|h,k| h[k] = Set::new}
work_types[ nsc_id ] << work_type
but you must understand set and it's notion of equality. plus you lose data
order but, since you are ignoring dups, i guess this isn't important.
or perhaps you can model your data with a nested hash?
work_types = Hash::new{|h,k| h[k] = {}}
work_types[ nsc_id ][ work_type ] = true
and then use
values = work_types[ nsc_id ].keys
or just make your own apprach more compact
work_types = Hash::new
work_types[ nsc_id ] = [ work_types[ nsc_id ], work_type ].compact.uniq
you have options - and there is always sqlite if you start to feel like you
are rolling query logic on top of this data structure
regards.
-a
···
On Wed, 12 Oct 2005, Kev Jackson wrote:
I got the output I wanted with this
work_types = Hash.new
if work_types.has_key?(nsc_id) then
work_types[nsc_id]= work_types[nsc_id].include?(work_type) ? work_types[nsc_id] : work_types[nsc_id] << work_type
else
work_types[nsc_id]= [work_type]
end
So the problem is solved, but I wonder if there's a more elegant way of
doing it (especially the check to see if the value is already in the array).
My first assumption was that assignment to a Hash took a block (hence the
pseudo code), I was actually a little suprised that it didn't
--
email :: ara [dot] t [dot] howard [at] noaa [dot] gov
phone :: 303.497.6469
Your life dwells amoung the causes of death
Like a lamp standing in a strong breeze. --Nagarjuna
===============================================================================
Ara.T.Howard wrote:
I got the output I wanted with this
work_types = Hash.new
if work_types.has_key?(nsc_id) then
work_types[nsc_id]= work_types[nsc_id].include?(work_type) ? work_types[nsc_id] : work_types[nsc_id] << work_type
else
work_types[nsc_id]= [work_type]
end
So the problem is solved, but I wonder if there's a more elegant way of
doing it (especially the check to see if the value is already in the array).
My first assumption was that assignment to a Hash took a block (hence the
pseudo code), I was actually a little suprised that it didn't
this is one easy way
work_types = Hash::new{|h,k| h[k] = }
work_types[ nsc_id ].push( work_type ).uniq!
That looks promising - I see it essentially relies on defining Hash and setting the initial values, so that I can avoid the "else work_types[nsc_id]= [work_type] end" part
uniq! certainly looks like it would shorten my code.
but does a bit of extra work. another way would be to use set
require 'set'
work_types = Hash::new{|h,k| h[k] = Set::new}
work_types[ nsc_id ] << work_type
Yeah I was thinking of Set, but I want to require/include as little as possible to keep complexity down for other people to maintain.
but you must understand set and it's notion of equality. plus you lose data
order but, since you are ignoring dups, i guess this isn't important.
or perhaps you can model your data with a nested hash?
work_types = Hash::new{|h,k| h[k] = {}}
work_types[ nsc_id ][ work_type ] = true
and then use
values = work_types[ nsc_id ].keys
or just make your own apprach more compact
work_types = Hash::new
work_types[ nsc_id ] = [ work_types[ nsc_id ], work_type ].compact.uniq
I'm not how this works in a manner that's similar to the (verbose but easy to understand) version I have already. In fact I can't understand half of what's going on here!
you have options - and there is always sqlite if you start to feel like you
are rolling query logic on top of this data structure
Dear god no! :). I'm only munging data dumps from Oracle, I'd hate to have to store them in a database just to transform them!
Kev
···
On Wed, 12 Oct 2005, Kev Jackson wrote: