Ruby: Easiest Way to Filter Hash Keys?
RubyRuby Problem Overview
I have a hash that looks something like this:
params = { :irrelevant => "A String",
:choice1 => "Oh look, another one",
:choice2 => "Even more strings",
:choice3 => "But wait",
:irrelevant2 => "The last string" }
And I want a simple way to reject all the keys that aren't choice+int. It could be choice1, or choice1 through choice10. It varies.
How do I single out the keys with just the word choice and a digit or digits after them?
Bonus:
Turn the hash into a string with tab (\t) as a delimiter. I did this, but it took several lines of code. Usually master Rubicians can do it in one or so lines.
Ruby Solutions
Solution 1 - Ruby
Edit to original answer: Even though this is answer (as of the time of this comment) is the selected answer, the original version of this answer is outdated.
I'm adding an update here to help others avoid getting sidetracked by this answer like I did.
As the other answer mentions, Ruby >= 2.5 added the Hash#slice
method which was previously only available in Rails.
Example:
> { one: 1, two: 2, three: 3 }.slice(:one, :two)
=> {:one=>1, :two=>2}
End of edit. What follows is the original answer which I guess will be useful if you're on Ruby < 2.5 without Rails, although I imagine that case is pretty uncommon at this point.
If you're using Ruby, you can use the select
method. You'll need to convert the key from a Symbol to a String to do the regexp match. This will give you a new Hash with just the choices in it.
choices = params.select { |key, value| key.to_s.match(/^choice\d+/) }
or you can use delete_if
and modify the existing Hash e.g.
params.delete_if { |key, value| !key.to_s.match(/choice\d+/) }
or if it is just the keys and not the values you want then you can do:
params.keys.select { |key| key.to_s.match(/^choice\d+/) }
and this will give the just an Array of the keys e.g. [:choice1, :choice2, :choice3]
Solution 2 - Ruby
In Ruby, the Hash#select is a right option. If you work with Rails, you can use Hash#slice and Hash#slice!. e.g. (rails 3.2.13)
h1 = {:a => 1, :b => 2, :c => 3, :d => 4}
h1.slice(:a, :b) # return {:a=>1, :b=>2}, but h1 is not changed
h2 = h1.slice!(:a, :b) # h1 = {:a=>1, :b=>2}, h2 = {:c => 3, :d => 4}
Solution 3 - Ruby
The easiest way is to include the gem 'activesupport'
(or gem 'active_support'
).
Then, in your class you only need to
require 'active_support/core_ext/hash/slice'
and to call
params.slice(:choice1, :choice2, :choice3) # => {:choice1=>"Oh look, another one", :choice2=>"Even more strings", :choice3=>"But wait"}
I believe it's not worth it to be declaring other functions that may have bugs, and it's better to use a method that has been tweaked during last few years.
Solution 4 - Ruby
If you work with rails and you have the keys in a separate list, you can use the *
notation:
keys = [:foo, :bar]
hash1 = {foo: 1, bar:2, baz: 3}
hash2 = hash1.slice(*keys)
=> {foo: 1, bar:2}
As other answers stated, you can also use slice!
to modify the hash in place (and return the erased key/values).
Solution 5 - Ruby
The easiest way is to include the gem 'activesupport' (or gem 'active_support').
params.slice(:choice1, :choice2, :choice3)
Solution 6 - Ruby
This is a one line to solve the complete original question:
params.select { |k,_| k[/choice/]}.values.join('\t')
But most the solutions above are solving a case where you need to know the keys ahead of time, using slice
or simple regexp.
Here is another approach that works for simple and more complex use cases, that is swappable at runtime
data = {}
matcher = ->(key,value) { COMPLEX LOGIC HERE }
data.select(&matcher)
Now not only this allows for more complex logic on matching the keys or the values, but it is also easier to test, and you can swap the matching logic at runtime.
Ex to solve the original issue:
def some_method(hash, matcher)
hash.select(&matcher).values.join('\t')
end
params = { :irrelevant => "A String",
:choice1 => "Oh look, another one",
:choice2 => "Even more strings",
:choice3 => "But wait",
:irrelevant2 => "The last string" }
some_method(params, ->(k,_) { k[/choice/]}) # => "Oh look, another one\\tEven more strings\\tBut wait"
some_method(params, ->(_,v) { v[/string/]}) # => "Even more strings\\tThe last string"
Solution 7 - Ruby
With Hash::select
:
params = params.select { |key, value| /^choice\d+$/.match(key.to_s) }
Solution 8 - Ruby
If you want the remaining hash:
params.delete_if {|k, v| ! k.match(/choice[0-9]+/)}
or if you just want the keys:
params.keys.delete_if {|k| ! k.match(/choice[0-9]+/)}
Solution 9 - Ruby
With Hash Slice
{ a: 1, b: 2, c: 3, d: 4 }.slice(:a, :b)
# => {:a=>1, :b=>2}
# If you have an array of keys you want to limit to, you should splat them:
valid_keys = [:mass, :velocity, :time]
search(options.slice(*valid_keys))
Solution 10 - Ruby
Put this in an initializer
class Hash
def filter(*args)
return nil if args.try(:empty?)
if args.size == 1
args[0] = args[0].to_s if args[0].is_a?(Symbol)
self.select {|key| key.to_s.match(args.first) }
else
self.select {|key| args.include?(key)}
end
end
end
Then you can do
{a: "1", b: "b", c: "c", d: "d"}.filter(:a, :b) # => {a: "1", b: "b"}
or
{a: "1", b: "b", c: "c", d: "d"}.filter(/^a/) # => {a: "1"}
Solution 11 - Ruby
params.select{ |k,v| k =~ /choice\d/ }.map{ |k,v| v}.join("\t")
Solution 12 - Ruby
As for bonus question:
-
If you have output from
#select
method like this (list of 2-element arrays):[[:choice1, "Oh look, another one"], [:choice2, "Even more strings"], [:choice3, "But wait"]]
then simply take this result and execute:
filtered_params.join("\t")
# or if you want only values instead of pairs key-value
filtered_params.map(&:last).join("\t")
2. If you have output from #delete_if
method like this (hash):
{:choice1=>"Oh look, another one", :choice2=>"Even more strings", :choice3=>"But wait"}
then:
filtered_params.to_a.join("\t")
# or
filtered_params.values.join("\t")
Solution 13 - Ruby
params = { :irrelevant => "A String",
:choice1 => "Oh look, another one",
:choice2 => "Even more strings",
:choice3 => "But wait",
:irrelevant2 => "The last string" }
choices = params.select { |key, value| key.to_s[/^choice\d+/] }
#=> {:choice1=>"Oh look, another one", :choice2=>"Even more strings", :choice3=>"But wait"}
Solution 14 - Ruby
I had a similar problem, in my case the solution was a one liner which works even if the keys aren't symbols, but you need to have the criteria keys in an array
criteria_array = [:choice1, :choice2]
params.select { |k,v| criteria_array.include?(k) } #=> { :choice1 => "Oh look another one",
:choice2 => "Even more strings" }
Another example
criteria_array = [1, 2, 3]
params = { 1 => "A String",
17 => "Oh look, another one",
25 => "Even more strings",
49 => "But wait",
105 => "The last string" }
params.select { |k,v| criteria_array.include?(k) } #=> { 1 => "A String"}