{"key_a" => "value_a", "key_b" => "value_b", "key_c" => { "key_c_a" => nil, "key_c_b" => nil, "key_c_c" => "value_c_c"}, "key_d" => nil, "key_e" => nil }
how do i map the hash such that i get the result as "key_c_a", "key_c_b", "key_d" and key_e"?
i keep getting my answer as an empty array and here is the method in the module that is used in the main class
def self.get_null_keys(container)
container.map do |key, value|
if value.is_a?(Array)
value.map { |field| render_null_fields(field) }
elsif value.is_a?(Hash)
render_null_fields(value)
elsif value.nil?
key
end
end
end
Naive recursive way to do it:
hash = {"key_a" => "value_a", "key_b" => "value_b", "key_c" => { "key_c_a" => nil, "key_c_b" => nil, "key_c_c" => "value_c_c"}, "key_d" => nil, "key_e" => nil }
def get_null_values(hash, array = [])
hash.each do |key, value|
array << key if value.nil?
get_null_values(value, array) if value.is_a?(Hash)
end
array
end
get_null_values(hash) # ["key_c_a", "key_c_b", "key_d", "key_e"]
Do it recursively:
h={"key_a" => "value_a", "key_b" => "value_b", "key_c" => { "key_c_a" => nil, "key_c_b" => nil, "key_c_c" => "value_c_c"}, "key_d" => nil, "key_e" => nil }
def find_nils(x, memo=[])
x.inject({}){ |m, (k, v)|
v = find_nils(v, memo) if v.is_a? Hash # arbitrarily recursive
memo << k if v.nil?
}
memo
end
Instead of inject as a skeleton you can also use each:
def find_nils(x, memo=[])
x.each{ |k, v|
v = find_nils(v, memo) if v.is_a? Hash # arbitrarily recursive
memo << k if v.nil?
}
memo
end
Either:
p find_nils(h)
["key_c_a", "key_c_b", "key_d", "key_e"]
Related
t = {
"Bachelor" => [1,2,3],
"Master" => [4,5,6]
}
r = t.invert
=> {[1, 2, 3]=>"Bachelor", [4, 5, 6]=>"Master"}
r[1]
=> nil
My question is, how do I access the value for key 1,2 etc in the example mentioned?
How to convert this to: {"1"=> "Bachelor","2"=> "Bachelor"..} etc?
res = t.each_with_object({}) do |(key, vals), res|
vals.each do |val|
res[val] = key
end
end
res[1]
=> "Bachelor"
res
=> {1=>"Bachelor", 2=>"Bachelor", 3=>"Bachelor", 4=>"Master", 5=>"Master", 6=>"Master"}
You could give your hash a default procedure which runs whenever the key can't be found:
t = {
"Bachelor" => [1,2,3],
"Master" => [4,5,6]
}
r = t.invert
r.default_proc = proc do |hash, key|
hash.find{|k,v| k.include?(key) }.last
end
#demo:
puts r[5] # => Master
Another useful mechanism which does not use a hash is a case when construct:
num=5
title = case num
when 1..3 then "Bachelor"
when 4..6 then "Master"
end
You could create a new hash by iterating through the array keys of t.invert:
h = t.invert.map do |k,v|
k.map {|kk| {kk => v} } }.flatten.inject(:merge)
=> {1=>"Bachelor", 2=>"Bachelor", 3=>"Bachelor", 4=>"Master", 5=>"Master", 6=>"Master"}
h[1]
=> "Bachelor"
res = {}
t.each { |key, values| values.inject(res) { |h, i| h[i] = key; h }}
res[1]
=> "Bachelor"
res
=> {1=>"Bachelor", 2=>"Bachelor", 3=>"Bachelor", 4=>"Master", 5=>"Master", 6=>"Master"}
With this code I implemented a tree
groups = {"al1o0"=>"A1", "al2o2"=>"A10", "al2o3"=>"A11", "al1o1"=>"A2"}
map = {}
arr = []
groups.each_with_index do |group, index|
level = (group.first.split("o")[0].split("al")[1]).to_i - 1
level = level == 0 ? nil : level
order = group.first.split("o")[1]
arr.append({ :id=> index + 1, :order => order, :name => group.last, :parent => level})
end
root = {:id => 0, :name => '', :order => 0, :parent => nil}
arr.each do |e|
map[e[:id]] = e
end
tree = {}
arr.each do |e|
pid = e[:parent]
if pid == nil
(tree[root] ||= []) << e
else
(tree[map[pid]] ||= []) << e
end
end
tree has
=> {{:id=>0, :name=>"", :order=>0, :parent=>nil}=>[{:id=>1, :order=>"0", :name=>"A1", :parent=>nil}, {:id=>4, :order=>"1", :name=>"A2", :parent=>nil}], {:id=>1, :order=>"0", :name=>"A1", :parent=>nil}=>[{:id=>2, :order=>"2", :name=>"A10", :parent=>1}, {:id=>3, :order=>"3", :name=>"A11", :parent=>1}]}
Up to here all right but If I do tree.to_json, the output is
=> "{\"{:id=\\u003e0, :name=\\u003e\\\"\\\", :order=\\u003e0, :parent=\\u003enil}\":[{\"id\":1,\"order\":\"0\",\"name\":\"A1\",\"parent\":null},{\"id\":4,\"order\":\"1\",\"name\":\"A2\",\"parent\":null}],\"{:id=\\u003e1, :order=\\u003e\\\"0\\\", :name=\\u003e\\\"A1\\\", :parent=\\u003enil}\":[{\"id\":2,\"order\":\"2\",\"name\":\"A10\",\"parent\":1},{\"id\":3,\"order\":\"3\",\"name\":\"A11\",\"parent\":1}]}"
Why It changed :id=>0 in :id=\u003e0?
First of all tree looks weird.
{{:id=>0, :name=>"", :order=>0, :parent=>nil}=>[{:id=>1, :order=>"0", :name=>"A1", :parent=>nil}, ...]}}
here is a key
{:id=>0, :name=>"", :order=>0, :parent=>nil}
and
[{:id=>1, :order=>"0", :name=>"A1", :parent=>nil}, ...]
is a value.
Key should not be a hash. How to call it later then.
You might need something like
{"A1" => {name: 'foo', order: '0' }, 'A2' => ...}
I have this hash:
HASH = {
'x' => { :amount => 0 },
'c' => { :amount => 5 },
'q' => { :amount => 10 },
'y' => { :amount => 20 },
'n' => { :amount => 50 }
}
How can I get the key with the next highest amount from the hash?
For example, if I supply x, it should return c. If there is no higher amount, then the key with the lowest amount should be returned. That means when I supply n, then x would be returned.
Can anybody help?
I'd use something like this:
def next_higher(key)
amount = HASH[key][:amount]
sorted = HASH.sort_by { |_, v| v[:amount] }
sorted.find(sorted.method(:first)) { |_, v| v[:amount] > amount }.first
end
next_higher "x" #=> "c"
next_higher "n" #=> "x"
I'd do something like this:
def find_next_by_amount(hash, key)
sorted = hash.sort_by { |_, v| v[:amount] }
index_of_next = sorted.index { |k, _| k == key }.next
sorted.fetch(index_of_next, sorted.first).first
end
find_next_by_amount(HASH, 'x')
# => "c"
find_next_by_amount(HASH, 'n')
# => "x"
Something like that:
def next(key)
amount = HASH[key][:amount]
kv_pairs = HASH.select{ |k, v| v[:amount] > amount }
result = kv_pairs.empty? ? HASH.first.first : kv_pairs.min_by{ |k, v| v}.first
end
I'm curious, why would you want something like that? Maybe there is better solution to underlying task.
EDIT: Realized that hash isn't necessary sorted by amount, adapted code for unsorted hashes.
One way:
A = HASH.sort_by { |_,h| h[:amount] }.map(&:first)
#=> ['x', 'c', 'q', 'y', 'n']
(If HASH's keys are already in the correct order, this is is just A = HASH.keys.)
def next_one(x)
A[(A.index(x)+1)%A.size]
end
next_one 'x' #=> 'c'
next_one 'q' #=> 'y'
next_one 'n' #=> 'x'
Alternatively, you could create a hash instead of a method:
e = A.cycle
#=> #<Enumerator: ["x", "c", "q", "y", "n"]:cycle>
g = A.size.times.with_object({}) { |_,g| g.update(e.next=>e.peek) }
#=> {"x"=>"c", "c"=>"q", "q"=>"y", "y"=>"n", "n"=>"x"}
What is the best way to construct a hash-like class Case, which is initialized by a hash:
cs = Case.new(:a => 1, /b/ => 2, /c/ => 2, /d/ => 3)
and has a method Case#[] that looks up for the first matching key by === (like a case statement) instead of by == (like the conventional hash) and returns the value:
cs["xxb"] => 2
Here's a possibility.
class Case
def initialize(h)
#h = h
end
def [](key,order=:PRE)
case order
when :PRE
h[#h.keys.find { |k| key === k }]
when :POST
h[#h.keys.find { |k| k === key }]
else
# raise exception
end
end
end
cs = Case.new(:a => 1, /b/ => 2, /c/ => 2, [1,2] => "cat", /d/ => 3)
cs["xxb"] #=> nil
cs["xxb",:POST] #=> 2
cs[Regexp] #=> 2
cs[Regexp,:POST] #=> nil
cs[Array] #=> "cat"
cs[Symbol] #=> 1
This assumes h does not have a key nil.
With the understanding that the key in the hash is to come on the left side of ===, the code would be:
class Case
def initialize(h) #h = h end
def [](key) h[#h.keys.find{|k| k === key}] end
end
I have a Ruby hash which looks like:
{ "id" => "123", "name" => "test" }
I would like to convert it to:
{ :id => "123", :name => "test" }
hash = {"apple" => "banana", "coconut" => "domino"}
Hash[hash.map{ |k, v| [k.to_sym, v] }]
#=> {:apple=>"banana", :coconut=>"domino"}
#mu is too short: Didn't see word "recursive", but if you insist (along with protection against non-existent to_sym, just want to remind that in Ruby 1.8 1.to_sym == nil, so playing with some key types can be misleading):
hash = {"a" => {"b" => "c"}, "d" => "e", Object.new => "g"}
s2s =
lambda do |h|
Hash === h ?
Hash[
h.map do |k, v|
[k.respond_to?(:to_sym) ? k.to_sym : k, s2s[v]]
end
] : h
end
s2s[hash] #=> {:d=>"e", #<Object:0x100396ee8>=>"g", :a=>{:b=>"c"}}
If you happen to be in Rails then you'll have symbolize_keys:
Return a new hash with all keys converted to symbols, as long as they respond to to_sym.
and symbolize_keys! which does the same but operates in-place. So, if you're in Rails, you could:
hash.symbolize_keys!
If you want to recursively symbolize inner hashes then I think you'd have to do it yourself but with something like this:
def symbolize_keys_deep!(h)
h.keys.each do |k|
ks = k.to_sym
h[ks] = h.delete k
symbolize_keys_deep! h[ks] if h[ks].kind_of? Hash
end
end
You might want to play with the kind_of? Hash to match your specific circumstances; using respond_to? :keys might make more sense. And if you want to allow for keys that don't understand to_sym, then:
def symbolize_keys_deep!(h)
h.keys.each do |k|
ks = k.respond_to?(:to_sym) ? k.to_sym : k
h[ks] = h.delete k # Preserve order even when k == ks
symbolize_keys_deep! h[ks] if h[ks].kind_of? Hash
end
end
Note that h[ks] = h.delete k doesn't change the content of the Hash when k == ks but it will preserve the order when you're using Ruby 1.9+. You could also use the [(key.to_sym rescue key) || key] approach that Rails uses in their symbolize_keys! but I think that's an abuse of the exception handling system.
The second symbolize_keys_deep! turns this:
{ 'a' => 'b', 'c' => { 'd' => { 'e' => 'f' }, 'g' => 'h' }, ['i'] => 'j' }
into this:
{ :a => 'b', :c => { :d => { :e => 'f' }, :g => 'h' }, ['i'] => 'j' }
You could monkey patch either version of symbolize_keys_deep! into Hash if you really wanted to but I generally stay away from monkey patching unless I have very good reasons to do it.
If you are using Rails >= 4 you can use:
hash.deep_symbolize_keys
hash.deep_symbolize_keys!
or
hash.deep_stringify_keys
hash.deep_stringify_keys!
see http://apidock.com/rails/v4.2.1/Hash/deep_symbolize_keys
Just in case you are parsing JSON, from the JSON docs you can add the option to symbolize the keys upon parsing:
hash = JSON.parse(json_data, symbolize_names: true)
Victor Moroz provided a lovely answer for the simple recursive case, but it won't process hashes that are nested within nested arrays:
hash = { "a" => [{ "b" => "c" }] }
s2s[hash] #=> {:a=>[{"b"=>"c"}]}
If you need to support hashes within arrays within hashes, you'll want something more like this:
def recursive_symbolize_keys(h)
case h
when Hash
Hash[
h.map do |k, v|
[ k.respond_to?(:to_sym) ? k.to_sym : k, recursive_symbolize_keys(v) ]
end
]
when Enumerable
h.map { |v| recursive_symbolize_keys(v) }
else
h
end
end
Try this:
hash = {"apple" => "banana", "coconut" => "domino"}
# => {"apple"=>"banana", "coconut"=>"domino"}
hash.tap do |h|
h.keys.each { |k| h[k.to_sym] = h.delete(k) }
end
# => {:apple=>"banana", :coconut=>"domino"}
This iterates over the keys, and for each one, it deletes the stringified key and assigns its value to the symbolized key.
If you're using Rails (or just Active Support):
{ "id" => "123", "name" => "test" }.symbolize_keys
Starting with Ruby 2.5 you can use the transform_key method.
So in your case it would be:
h = { "id" => "123", "name" => "test" }
h.transform_keys!(&:to_sym) #=> {:id=>"123", :name=>"test"}
Note: the same methods are also available on Ruby on Rails.
Here's a Ruby one-liner that is faster than the chosen answer:
hash = {"apple" => "banana", "coconut" => "domino"}
#=> {"apple"=>"banana", "coconut"=>"domino"}
hash.inject({}){|h,(k,v)| h[k.intern] = v; h}
#=> {:apple=>"banana", :coconut=>"domino"}
Benchmark results:
n = 100000
Benchmark.bm do |bm|
bm.report { n.times { hash.inject({}){|h,(k,v)| h[k.intern] = v; h} } }
bm.report { n.times { Hash[hash.map{ |k, v| [k.to_sym, v] }] } }
end
# => user system total real
# => 0.100000 0.000000 0.100000 ( 0.107940)
# => 0.120000 0.010000 0.130000 ( 0.137966)
I'm partial to:
irb
ruby-1.9.2-p290 :001 > hash = {"apple" => "banana", "coconut" => "domino"}
{
"apple" => "banana",
"coconut" => "domino"
}
ruby-1.9.2-p290 :002 > hash.inject({}){ |h, (n,v)| h[n.to_sym] = v; h }
{
:apple => "banana",
:coconut => "domino"
}
This works because we're iterating over the hash and building a new one on the fly. It isn't recursive, but you could figure that out from looking at some of the other answers.
hash.inject({}){ |h, (n,v)| h[n.to_sym] = v; h }
You can also extend core Hash ruby class placing a /lib/hash.rb file :
class Hash
def symbolize_keys_deep!
new_hash = {}
keys.each do |k|
ks = k.respond_to?(:to_sym) ? k.to_sym : k
if values_at(k).first.kind_of? Hash or values_at(k).first.kind_of? Array
new_hash[ks] = values_at(k).first.send(:symbolize_keys_deep!)
else
new_hash[ks] = values_at(k).first
end
end
new_hash
end
end
If you want to make sure keys of any hash wrapped into arrays inside your parent hash are symbolized, you need to extend also array class creating a "array.rb" file with that code :
class Array
def symbolize_keys_deep!
new_ar = []
self.each do |value|
new_value = value
if value.is_a? Hash or value.is_a? Array
new_value = value.symbolize_keys_deep!
end
new_ar << new_value
end
new_ar
end
end
This allows to call "symbolize_keys_deep!" on any hash variable like this :
myhash.symbolize_keys_deep!
def symbolize_keys(hash)
new={}
hash.map do |key,value|
if value.is_a?(Hash)
value = symbolize_keys(value)
end
new[key.to_sym]=value
end
return new
end
puts symbolize_keys("c"=>{"a"=>2,"k"=>{"e"=>9}})
#{:c=>{:a=>2, :k=>{:e=>9}}}
Here's my two cents,
my version of symbolize_keys_deep! uses the original symbolize_keys! provided by rails and just makes a simple recursive call to Symbolize sub hashes.
def symbolize_keys_deep!(h)
h.symbolize_keys!
h.each do |k, v|
symbolize_keys_deep!(v) if v.is_a? Hash
end
end
Facets' Hash#rekey is also a worth mentioning.
Sample:
require 'facets/hash/rekey'
{ "id" => "123", "name" => "test" }.deep_rekey
=> {:id=>"123", :name=>"test"}
There is also a recursive version:
require 'facets/hash/deep_rekey'
{ "id" => "123", "name" => {"first" => "John", "last" => "Doe" } }.deep_rekey
=> {:id=>"123", :name=>{:first=>"John", :last=>"Doe"}}
Here's a little recursive function to do a deep symbolization of the keys:
def symbolize_keys(hash)
Hash[hash.map{|k,v| v.is_a?(Hash) ? [k.to_sym, symbolize_keys(v)] : [k.to_sym, v] }]
end