I have a db query which returns results like:
db_result.each {|row| puts row}
{"IP"=>"1.2.3.4","Field1"=>"abc","Field2"=>"123"}
{"IP"=>"1.2.3.4","Field1"=>"abc","Field2"=>"234"}
{"IP"=>"1.2.3.4","Field1"=>"bcd","Field2"=>"345"}
{"IP"=>"3.4.5.6","Field1"=>"bcd","Field2"=>"456"}
{"IP"=>"3.4.5.6","Field1"=>"bcd","Field2"=>"567"}
And want to put it into a hash like:
{
"1.2.3.4" => {
"abc" => ["123", "234"],
"bcd" => "345"
},
"3.4.5.6" => {
"bcd" => ["456", "567"]
}
}
What I am currently doing is:
result_hash = Hash.new { |h, k| h[k] = {} }
db_result.each do |row|
result_hash[row["IP"]] = Hash.new { |h, k| h[k] = [] } unless result_hash.has_key? row["IP"]
result_hash[row["IP"]][row["Field1"]] << row["Field2"]
end
Which works, however was wondering if there is a neater way.
Consider this a peer-review. As a recommendation for processing and maintenance...
I'd recommend the data structure you want be a little more consistent.
Instead of:
{
"1.2.3.4" => {
"abc" => ["123", "234"],
"bcd" => "345"
},
"3.4.5.6" => {
"bcd" => ["456", "567"]
}
}
I'd recommend:
{
"1.2.3.4" => {
"abc" => ["123", "234"],
"bcd" => ["345"]
},
"3.4.5.6" => {
"abc" => [],
"bcd" => ["456", "567"]
}
}
Keep the same keys in each sub-hash, and make the values all be arrays. The code for processing that overall hash will be more straightforward and easy to follow.
I agree with Michael, there is nothing wrong with your method. The intent behind the code can be easily seen.
If you want to get fancy, here's one (of many) ways to do it:
x = [
{"IP"=>"1.2.3.4","Field1"=>"abc","Field2"=>"123"},
{"IP"=>"1.2.3.4","Field1"=>"abc","Field2"=>"234"},
{"IP"=>"1.2.3.4","Field1"=>"bcd","Field2"=>"345"},
{"IP"=>"3.4.5.6","Field1"=>"bcd","Field2"=>"456"},
{"IP"=>"3.4.5.6","Field1"=>"bcd","Field2"=>"567"}
]
y = x.inject({}) do |result, row|
new_row = result[row["IP"]] ||= {}
(new_row[row["Field1"]] ||= []) << row["Field2"]
result
end
I think this should yield the same time complexity as your method.
Related
I have this data:
input = [ [ 'abc', '1.1' ], [ 'abc', '1.2' ], [ 'xyz', '3.14' ] ]
I would like output like the following:
[ { 'abc' => [ '1.1', '1.2' ] }, { 'xyz' => '3.14' } ]
Is it possible to achieve this in one chained expression?
I'd do it like this:
input = [['abc', '1.1'], ['abc','1.2'], ['xyz', '3.14']]
output = input.each_with_object(Hash.new{ |h, k| h[k] = [] }) { |(k, v), h| h[k] << v }
output # => {"abc"=>["1.1", "1.2"], "xyz"=>["3.14"]}
An alternate, which isn't as straightforward is:
input.group_by{ |k,v| k }.map{ |k, v| [k, v.map(&:last)] }.to_h # => {"abc"=>["1.1", "1.2"], "xyz"=>["3.14"]}
Your output structure
output: [{'abc' => ['1.1', '1.2']}, {'xyz' => '3.14'}]
is a very poor way to use a hash. Instead, you should have one hash, with multiple elements, since you're combining the like-key's values into one key.
If you REALLY need the output that way, as some seem to think, then simply append a map to the returned value:
input.each_with_object(Hash.new{ |h, k| h[k] = [] }) { |(k, v), h| h[k] << v }.map{ |k, v| {k => v} }
# => [{"abc"=>["1.1", "1.2"]}, {"xyz"=>["3.14"]}]
Simplest way I could think of:
input.group_by {|x| x[0]}.each_pair.map { |k, v| {k => (a=v.map(&:last)).count > 1 ? a : a[0]} }
The simplest way to do it is like this:
def convert_marray_to_hash(input)
hash = Hash.new { |hash, key| hash[key] = [] }
output = []
input.each { |array| hash[array[0]] << array[1] }
hash.keys.each { |key| output << { key => hash[key] } }
output
end
There are many ways to do it, but that way presents itself nicely and is readable.
This works pretty well:
input = [ [ 'abc', '1.1' ], [ 'abc','1.2' ], [ 'xyz', '3.14' ] ]
input.each_with_object({}) do |(key, val), hsh|
hsh[key] = val and next unless hsh.key?(key)
hsh[key] = [ *hsh[key], val ]
end
.map {|key, val| { key => val } }
# => [ { "abc" => [ "1.1", "1.2" ] },
# { "xyz" => "3.14" }
# ]
If you omit the final map you end up with a hash, which seems like a more natural result, but this matches the output specified, at least.
I have a big hash with lots of nested key value pairs.
Eg.
h = {"foo" => {"bar" => {"hello" => {"world" => "result" } } } }
Now I want to access result and I have keys for that in array in proper sequence.
keys_arr = ["foo", "bar", "hello", "world"]
The motive is clear, I want to do following:
h["foo"]["bar"]["hello"]["world"]
# => "result"
But I don't know how to do this. I am currently doing:
key = '["' + keys_arr.join('"]["') + '"]'
eval("h"+key)
# => "result"
Which looks like a hack. Also it greatly reduces my ability to work with hash in real environment.
Please suggest alternate and better ways.
Using Enumerable#inject (or Enumerable#reduce):
h = {"foo" => {"bar" => {"hello" => {"world" => "result" } } } }
keys_arr = ["foo", "bar", "hello", "world"]
keys_arr.inject(h) { |x, k| x[k] }
# => "result"
UPDATE
If you want to do something like: h["foo"]["bar"]["hello"]["world"] = "ruby"
innermost = keys_arr[0...-1].inject(h) { |x, k| x[k] } # the innermost hash
innermost[keys_arr[-1]] = "ruby"
keys_arr.inject(h, :[])
will do
Another way:
h = {"foo" => {"bar" => {"hello" => {"world" => 10 } } } }
keys = ["foo", "bar", "hello", "world"]
result = h
keys.each do |key|
result = result[key]
end
puts result #=>10
If the key may not exist, see here:
Dealing with many [...] in Ruby
array = [{ name:'Joe', foo:'bar' },
{ name:'Bob', foo:'' },
{ name:'Hal', foo:'baz' }
]
What is an eloquent way to sort so that if foo is empty, then put it at the end, and not change the order of the other elements?
Ruby 1.9.3
array.partition { |h| !h[:foo].empty? }.flatten
array.find_all{|elem| !elem[:foo].empty?} + array.find_all{|elem| elem[:foo].empty?}
returns
[{:name=>"Joe", :foo=>"bar"}, {:name=>"Hal", :foo=>"baz"}, {:name=>"Bob", :foo=>""}]
array = [
{ name:'Joe', foo:'bar' },
{ name:'Bob', foo:'' },
{ name:'Hal', foo:'baz' }
]
arraydup = array.dup
array.delete_if{ |h| h[:foo].empty? }
array += (arraydup - array)
Which results in:
[
[0] {
:name => "Joe",
:foo => "bar"
},
[1] {
:name => "Hal",
:foo => "baz"
},
[2] {
:name => "Bob",
:foo => ""
}
]
With a little refactoring:
array += ((array.dup) - array.delete_if{ |h| h[:foo].empty? })
One can produce keys as tuples, where the first part indicates null/not-null, and the second part is the original index, then sort_by [nulls_last, original_index].
def sort_nulls_last_preserving_original_order array
array.map.with_index.
sort_by { |h,i| [ (h[:foo].empty? ? 1 : 0), i ] }.
map(&:first)
end
Note this avoids all the gross array mutation of some of the other answers and is constructed from pure functional transforms.
array.each_with_index do |item, index|
array << (array.delete_at(index)) if item[:foo].blank?
end
Use whatever you have in place of blank?.
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
I have a ruby hash that looks like this
{ "stuff_attributes" => {
"1" => {"foo" => "bar", "baz" => "quux"},
"2" => {"foo" => "bar", "baz" => "quux"}
}
}
and I want to turn it into a hash that looks like this
{ "stuff_attributes" => [
{ "foo" => "bar", "baz" => "quux"},
{ "foo" => "bar", "baz" => "quux"}
]
}
I also need to preserve the numerical order of the keys, and there is a variable number of keys. The above is super-simplified, but I've included a real example at the bottom. What's the best way to do this?
P.S
It also needs to be recursive
As far as the recursion goes, here's what we can assume:
1) the key that needs to be manipulated will match /_attributes$/
2) the hash will have many other keys that do not match /_attributes$/
3) the keys inside the hash will always be a number
4) an _attributes hash can be at any level of the hash under any other key
this hash is actually the params hash from a create action in the controller. This is a real example of what will need to be parsed with this routine.
{
"commit"=>"Save",
"tdsheet"=>{
"team_id"=>"43",
"title"=>"",
"performing_org_id"=>"10",
"tdsinitneed_attributes"=>{
"0"=>{
"title"=>"",
"need_date"=>"",
"description"=>"",
"expected_providing_organization_id"=>"41"
},
"1"=>{
"title"=>"",
"need_date"=>"",
"description"=>"",
"expected_providing_organization_id"=>"41"
}
},
"level_two_studycollection_id"=>"27",
"plan_attributes"=>{
"0"=>{
"start_date"=>"", "end_date"=>""
}
},
"dataitem_attributes"=>{
"0"=>{
"title"=>"",
"description"=>"",
"plan_attributes"=>{
"0"=>{
"start_date"=>"",
"end_date"=>""
}
}
},
"1"=>{
"title"=>"",
"description"=>"",
"plan_attributes"=>{
"0"=>{
"start_date"=>"",
"end_date"=>""
}
}
}
}
},
"action"=>"create",
"studycollection_level"=>"",
"controller"=>"tdsheets"
}
Note that this might be long to test if all keys are numbers before converting...
def array_from_hash(h)
return h unless h.is_a? Hash
all_numbers = h.keys.all? { |k| k.to_i.to_s == k }
if all_numbers
h.keys.sort_by{ |k| k.to_i }.map{ |i| array_from_hash(h[i]) }
else
h.each do |k, v|
h[k] = array_from_hash(v)
end
end
end
If we can assume that all the keys are in fact strings which convert cleanly to integers, the following ought to work:
# "hash" here refers to the main hash in your example, since you didn't name it
stuff_hash = hash["stuff"]
hash["stuff"] = stuff_hash.keys.sort_by {|key| key.to_i}.map {|key| stuff_hash[key]}
To take a bit of a liberty, I'm posting a very similar code example to Vincent Robert's.
This one is patches the Hash class with a .to_array method.
class Hash
def to_array(h = self)
return h unless h.is_a? Hash
if h.keys.all? { |k| k.to_i.to_s == k } # all keys are numbers so make an array.
h.keys.sort_by{ |k| k.to_i }.map{ |i| self.to_array(h[i]) }
else
h.each do |k, v|
h[k] = self.to_array(v)
end
end
end
end
It makes usage slightly more convenient.