Sorting on hash contents

ruby-talk
1

Hi, all.

Say I have a hash of 4 elements, val[1…3] and name

h[“a”] = "1,2,3,fred"
h[“b”] = "4,1,2,jack"
h[“c”] = “3,3,4,jill”

How do I define:

def sort_hash(field=“val1”)
h.each { |key, data|
(val1, val2, val3, name) = data.split(/,/)
# etc…
end

elegantly?

One possibility is to write it out to a tempfile and use
the external sort command. Is there an easy pure-ruby
solution?

TIA,

···

–
-mark.

2

Apparently, Mark Probert recently wrote:

Hi, all.

Say I have a hash of 4 elements, val[1…3] and name

h[“a”] = “1,2,3,fred”
h[“b”] = “4,1,2,jack”
h[“c”] = “3,3,4,jill”

How do I define:

def sort_hash(field=“val1”)
h.each { |key, data|
(val1, val2, val3, name) = data.split(/,/)
# etc…
end

elegantly?

One possibility is to write it out to a tempfile and use
the external sort command. Is there an easy pure-ruby
solution?

Not a full answer (no time right now), but run this in irb and it should
should give you some ideas:

h = {}
h[“a”] = “1,2,3,fred”
h[“b”] = “4,1,2,jack”
h[“c”] = “3,3,4,jill”
h.to_a
h.to_a.sort_by { |el| el[1].split(/,/)[0] }
h.to_a.sort_by { |el| el[1].split(/,/)[1] }
h.to_a.sort_by { |el| el[1].split(/,/)[2] }
h.to_a.sort_by { |el| el[1].split(/,/)[3] }

Wes

3

whenever i end up needing sorted hashes i ALWAYS use the rbtree package from
the raa - it is awesome. eg:

----CUT----
#!/usr/bin/env ruby
require ‘rbtree’ # get this from the raa - it’s FAST and always sorted

class DB < RBTree
attr :pks
alias pk pks
attr :fields
attr :n_pks
attr :n_fields
attr :indices
def initialize args
@pks = (args[:pks] or args[:pk]).to_a
@fields = args[:fields].to_a
pks.map{|k| raise unless fields.include? k}
@n_pks = pks.size
@n_fields = fields.size
@indices = {}
fields.map{|f| indices[f] = RBTree.new}
end
def = k, v
k, v = [k, v].map{|a| a.to_a}
raise unless k.size == pk.size and v.size == fields.size
# map each field back to this k->v pair…
@fields.each_with_index{|f,i| indices[f][v[i]] = [k,v]}
super k, v
end
def sorted_by field
raise unless block_given?
indices[field].map{|k,v| yield k, v}
end
end

db = DB.new :pk => ‘f0’, :fields => [‘f0’, ‘f1’, ‘f2’]

db[‘a’] = ‘0’, ‘C’, ‘b’
db[‘b’] = ‘1’, ‘B’, ‘a’
db[‘c’] = ‘2’, ‘A’, ‘c’

puts ‘–’
db.sorted_by(‘f0’) do |k,v|
p v
end

puts ‘–’
db.sorted_by(‘f1’) do |k,v|
p v
end

puts ‘–’
db.sorted_by(‘f2’) do |k,v|
p v
end

END
OUTPUT:

···

On Wed, 27 Aug 2003, Mark Probert wrote:

Hi, all.

Say I have a hash of 4 elements, val[1…3] and name

h[“a”] = “1,2,3,fred”
h[“b”] = “4,1,2,jack”
h[“c”] = “3,3,4,jill”

How do I define:

def sort_hash(field=“val1”)
h.each { |key, data|
(val1, val2, val3, name) = data.split(/,/)
# etc…
end

elegantly?

One possibility is to write it out to a tempfile and use
the external sort command. Is there an easy pure-ruby
solution?

TIA,

–
[[“a”], [“0”, “C”, “b”]]
[[“b”], [“1”, “B”, “a”]]
[[“c”], [“2”, “A”, “c”]]

[[“c”], [“2”, “A”, “c”]]
[[“b”], [“1”, “B”, “a”]]
[[“a”], [“0”, “C”, “b”]]

[[“b”], [“1”, “B”, “a”]]
[[“a”], [“0”, “C”, “b”]]
[[“c”], [“2”, “A”, “c”]]
----CUT----

-a

Ara Howard
NOAA Forecast Systems Laboratory
Information and Technology Services
Data Systems Group
R/FST 325 Broadway
Boulder, CO 80305-3328
Email: ara.t.howard@noaa.gov
Phone: 303-497-7238
Fax: 303-497-7259
~ > ruby -e ‘p(%.\x2d\x29…intern)’
====================================

4

I notice that rbtree works with Marshal, but not YAML. What methods
would have to be added to rbtree to fix this?

5

Currently, RBTree would need to inherit from Hash (or) introduce custom
is_complex_yaml?, to_yaml_type and to_yaml methods.

Here’s custom methods which appear to work:

Emitting the class

class RBTree
def to_yaml_type
“!ruby/rbtree”
end
def to_yaml( opts = {} )
YAML::quick_emit( self.object_id, opts ) { |out|
out.map( to_yaml_type ) { |map|
map.concat( self.to_a )
}
}
end
end

Loading the class

YAML.add_ruby_type( ‘rbtree’ ) { |type, val|
r = RBTree.new
val.each { |k, v| r[k] = v }
r
}

Test

a = RBTree[‘ducks’, 100, ‘bears’, 12, ‘badgers’, 0]
puts a.to_yaml
p YAML::load( a.to_yaml )

Looks like…

— !ruby/rbtree
badgers: 0
bears: 12
ducks: 100

I’m not very happy with this technique though. I’d rather it was simpler,
such as:

class RBTree
include YamlHashMixin
end

_why

···

On Thursday 28 August 2003 02:27 am, Joel VanderWerf wrote:

I notice that rbtree works with Marshal, but not YAML. What methods
would have to be added to rbtree to fix this?