How to pass a list of conditions as parameters

ruby-talk
1

I’m unsure how to explain this one so I'll do my best.

Technically, I would like to pass an array of numbers and an array of
conditions as parameters in a method. The tricky part is that I would
like to evaluate each number of that array to each condition of that
other array.

The reason I would like to achieve something like this is because I plan
to change the list of rules/conditions each time I want to call this
method.

Here’s the unworking code so far:

(see attachment)

Thank you in advance for your valuable support! Any help or hyperlinks
with explanations is greatly appreciated!

Attachments:
http://www.ruby-forum.com/attachment/6838/array_of_conditions.txt

···

--
Posted via http://www.ruby-forum.com/.

2

Nothing pretty or fancy here, but seems to do it? Note, I think the hash interpolation is a 1.9.x thing.

array_of_numbers = [0, 2, 4, 7, 10, 25]

# these could easily come from a config file/ db/ whatevs
array_of_eval_conditions = [ "(%{number} == 2)", "(%{number} == 5 and %{number} == 5)", "(%{number} != 1)"]

# these could too, but would require a few more hoops
array_of_lambda_conditions = [lambda {|x| x == 2}, lambda {|x| x == 5 and x == 5}, lambda {|x| x != 1}]

# for each number and condition, is it true when eval'ed?
def test_function_with_eval(numbers, conditions)
   numbers.each { |n|
     conditions.each { |c|
       puts ((eval(c%{:number=>n}))?"condition IS MET!":"condition is NOT met")
     }
   }
end

# for each number and condition, is it true when called?
def test_function_with_lambdas(numbers, conditions)
   numbers.each { |n|
     conditions.each { |c|
       puts ((c.call(n))?"condition IS MET!":"condition is NOT met")
     }
   }
end

puts "With eval!"
test_function_with_eval(array_of_numbers, array_of_eval_conditions)
puts "With lambdas!"
test_function_with_lambdas(array_of_numbers, array_of_lambda_conditions)

Sam

···

On 14/12/11 14:28, Thescholar Thescholar wrote:

I’m unsure how to explain this one so I'll do my best.

Technically, I would like to pass an array of numbers and an array of
conditions as parameters in a method. The tricky part is that I would
like to evaluate each number of that array to each condition of that
other array.

The reason I would like to achieve something like this is because I plan
to change the list of rules/conditions each time I want to call this
method.

Here’s the unworking code so far:

(see attachment)

Thank you in advance for your valuable support! Any help or hyperlinks
with explanations is greatly appreciated!

Attachments:
http://www.ruby-forum.com/attachment/6838/array_of_conditions.txt

3

Thank you very Sam! It seems there are still a lot more I need to learn
though.

For example, could you tell me where I could I learn more about this
part within the array? -----> %{number}

What keyword do I need to type on google to find more information about
this process?

Thank you again!

···

--
Posted via http://www.ruby-forum.com/.

4

The technology I'm using uses a version inferior to 1.9.x, fortunately
your example with lambda works like magic.

Your help was extremely helpful Sam! Thank you very much and Happy
Holidays! God Bless you (and every other members of this forum)!

···

--
Posted via http://www.ruby-forum.com/.

5

require 'pp'

def acond(avalues,aconditions)
  avalues.map { |n| [n,aconditions.map { |blk| blk.call(n) }] }
end

an = [0, 2, 4, 7, 10, 25, 6]
ac = [
  proc { |number| number == 2},
  proc { |number| number == 5 or number == 6},
  proc { |number| number!=1}
]

pp acond(an,ac)

···

--
Posted via http://www.ruby-forum.com/.

6

That is interpolating hash values in a string based on their key - it was just an easy way to get that number in the string twice and only specify it once =]
It is new in 1.9.x I believe and is similar to functionality found in python string interpolation with dicts.

Hope that helps

Sam

···

On 14/12/11 16:32, Thescholar Thescholar wrote:

Thank you very Sam! It seems there are still a lot more I need to learn
though.

For example, could you tell me where I could I learn more about this
part within the array? -----> %{number}

What keyword do I need to type on google to find more information about
this process?

Thank you again!

7

I’m unsure how to explain this one so I'll do my best.

Technically, I would like to pass an array of numbers and an array of
conditions as parameters in a method. The tricky part is that I would
like to evaluate each number of that array to each condition of that
other array.

The reason I would like to achieve something like this is because I plan
to change the list of rules/conditions each time I want to call this
method.

But what is the desired output? That's crucial for the solution (see below).

Here’s the unworking code so far:

(see attachment)

Thank you in advance for your valuable support! Any help or hyperlinks
with explanations is greatly appreciated!

Attachments:
http://www.ruby-forum.com/attachment/6838/array_of_conditions.txt

Nothing pretty or fancy here, but seems to do it? Note, I think the hash
interpolation is a 1.9.x thing.

array_of_numbers = [0, 2, 4, 7, 10, 25]

# these could easily come from a config file/ db/ whatevs
array_of_eval_conditions = [ "(%{number} == 2)", "(%{number} == 5 and
%{number} == 5)", "(%{number} != 1)"]

# these could too, but would require a few more hoops
array_of_lambda_conditions = [lambda {|x| x == 2}, lambda {|x| x == 5 and x
== 5}, lambda {|x| x != 1}]

Why "more hoops"? There is no point in having conditions in Strings
if they are constant in the script. There is no need for eval here.

Please note that an more recent versions of Ruby (at least 1.9.3)
lamba implements operator === which is reasonable because then you can
use a lambda as condition in a case expression and with
Enumerable#grep:

irb(main):004:0> pos = lambda {|x| x >= 0}
=> #<Proc:0x100e300c@(irb):4 (lambda)>
irb(main):005:0> vals = [-10,-5,0,5,10]
=> [-10, -5, 0, 5, 10]

irb(main):007:0> vals.each {|v| p v, pos[v], pos === v; case v;when
pos;puts "pos";else puts "not" end}
-10
false
false
not
-5
false
false
not
0
true
true
pos
5
true
true
pos
10
true
true
pos
=> [-10, -5, 0, 5, 10]

There do exists ways to do this already, e.g. assuming that conditions
are in an array of lambdas:

# get all which satisfy all conditions
items.select {|x| conditions.all? {|c| c[v]}}

# get first which satisfies all conditions
items.find {|x| conditions.all? {|c| c[v]}}

# get all which satisfy any condition
items.select {|x| conditions.any? {|c| c[v]}}

# get first which satisfies any condition
items.find {|x| conditions.any? {|c| c[v]}}

See also Enumerable#reject etc.

Kind regards

rober

···

On Wed, Dec 14, 2011 at 3:05 AM, Sam Duncan <sduncan@wetafx.co.nz> wrote:

On 14/12/11 14:28, Thescholar Thescholar wrote:

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

8

Having the expressions as strings means you can very easily load them from a data store or config file - the fact they are constant in this /example/ is incidental =]
This is not so easy with lambdas which was my point. It also lends itself to a simple boolean expression syntax which can conceivably be configured by a non-coder. The OP does not have 1.9.x by the way.

Sam

···

On 14/12/11 21:27, Robert Klemme wrote:

On Wed, Dec 14, 2011 at 3:05 AM, Sam Duncan<sduncan@wetafx.co.nz> wrote:

On 14/12/11 14:28, Thescholar Thescholar wrote:

I’m unsure how to explain this one so I'll do my best.

Technically, I would like to pass an array of numbers and an array of
conditions as parameters in a method. The tricky part is that I would
like to evaluate each number of that array to each condition of that
other array.

The reason I would like to achieve something like this is because I plan
to change the list of rules/conditions each time I want to call this
method.

But what is the desired output? That's crucial for the solution (see below).

Here’s the unworking code so far:

(see attachment)

Thank you in advance for your valuable support! Any help or hyperlinks
with explanations is greatly appreciated!

Attachments:
http://www.ruby-forum.com/attachment/6838/array_of_conditions.txt

Nothing pretty or fancy here, but seems to do it? Note, I think the hash
interpolation is a 1.9.x thing.

array_of_numbers = [0, 2, 4, 7, 10, 25]

# these could easily come from a config file/ db/ whatevs
array_of_eval_conditions = [ "(%{number} == 2)", "(%{number} == 5 and
%{number} == 5)", "(%{number} != 1)"]

# these could too, but would require a few more hoops
array_of_lambda_conditions = [lambda {|x| x == 2}, lambda {|x| x == 5 and x
== 5}, lambda {|x| x != 1}]

Why "more hoops"? There is no point in having conditions in Strings
if they are constant in the script. There is no need for eval here.

Please note that an more recent versions of Ruby (at least 1.9.3)
lamba implements operator === which is reasonable because then you can
use a lambda as condition in a case expression and with
Enumerable#grep:

irb(main):004:0> pos = lambda {|x| x>= 0}
=> #<Proc:0x100e300c@(irb):4 (lambda)>
irb(main):005:0> vals = [-10,-5,0,5,10]
=> [-10, -5, 0, 5, 10]

irb(main):007:0> vals.each {|v| p v, pos[v], pos === v; case v;when
pos;puts "pos";else puts "not" end}
-10
false
not
-5
false
not
0
true
pos
5
true
pos
10
true
pos
=> [-10, -5, 0, 5, 10]

There do exists ways to do this already, e.g. assuming that conditions
are in an array of lambdas:

# get all which satisfy all conditions
items.select {|x| conditions.all? {|c| c[v]}}

# get first which satisfies all conditions
items.find {|x| conditions.all? {|c| c[v]}}

# get all which satisfy any condition
items.select {|x| conditions.any? {|c| c[v]}}

# get first which satisfies any condition
items.find {|x| conditions.any? {|c| c[v]}}

See also Enumerable#reject etc.

Kind regards

rober

9

Having the expressions as strings means you can very easily load them from a
data store or config file - the fact they are constant in this /example/ is
incidental =]

But it helps understanding to explicitly mention this fact. That was
the whole point of the exercise.

The OP does not have 1.9.x by the way.

I think that was only relevant for my tangential remark about lambda
and === anyway.

Cheers

robert

···

On Wed, Dec 14, 2011 at 7:51 PM, Sam Duncan <sduncan@wetafx.co.nz> wrote:

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