I have a hash
hash = {"some_wierd_name"=>"cheesemonster", .....}
and I want this hash as
hash = {"preferred_name"=>"cheesemonster", ......}
What is the shortest way to do that?
hash["preferred_name"] = hash.delete("some_wierd_name")
Hash keys are frozen strings, they can’t be modified inplace, and the frozen state can’t be removed from an object. That said, tricks with prepend and replace won’t work resulting in:
RuntimeError: can't modify frozen String
Therefore, there is the only possibility: to remove the old value and insert the new one.
hash = {"some_wierd_name"=>"cheesemonster"}
hash["preferred_name"] = hash["some_wierd_name"]
hash.delete("some_wierd_name")
If we are looking to replace the key/value both, can be done easily by using rails except method. You can also use the delete method but one key/value pair at a time but be using except can remove 2 or more key/value pair.
hash = {a: 1, b:2, c: 3}
hash.except!(:a)[:d] = 4
and it is similar to these two following line
hash.except!(:a)
hash[:d] = 4
hash = {:b=>2, :c=>3, :d=>4}
Changing only key of the hash, value remains same. One can also use the reject. reject and delete_if are same.
hash[:e] = hash.delete(:d)
or
temp = hash[d]
hash.delete_if{|key| key ==:d }
hash[:e] = temp
hash = {:b=>2, :c=>3, :e=>4}
Changing only value, the key remains same. This one pretty easy.
hash[:e] = 5
References :
delete
except
hash
for a single key, use delete
hash["preferred_name"] = hash.delete("some_wierd_name")
If you need to update all the keys, i suggest using inject
new_hash = hash.inject({}) do |returned_hash, (key, value)|
returned_hash[key] = value.upcase;
returned_hash
end
Related
Given a source array of hashes:
[{:country=>'england', :cost=>12.34}, {:country=>'scotland', :cost=>56.78}]
Is there a neat Ruby one-liner for converting it to a single hash, where the values for the :country key in the original hash (guaranteed to be unique) become keys in the new hash?
{:england=>12.34, :scotland=>56.78}
This should do what you want
countries.each_with_object({}) { |country, h| h[country[:country].to_sym] = country[:cost] }
=> {:england=>12.34, :scotland=>56.78}
You can do that using Enumerable#inject:
countries.inject({}) { |hsh, element| hsh.merge!(element[:country].to_sym => element[:cost]) }
=> {:england=>12.34, :scotland=>56.78}
We initialise the accumulator as {}, and then we iterate over each of the elements of the initial array and add the new formatted element to the accumulator.
One point to add is that using hsh.merge or hsh.merge! would have the same effect for the output, given that inject will set the accumulator hsh as the return value from the block. However, using merge! is better when it comes to memory usage, given that merge will always generate a new Hash, whereas merge! will apply the merge over the same existing Hash.
One more possible solution is:
countries.map(&:values).to_h
=> {"england"=>12.34, "scotland"=>56.78}
I'm trying to get the index of a key in a hash.
I know how to do this in an array:
arr = ['Done', 13, 0.4, true]
a = arr.index('Done')
puts a
Is there a method or some sort of way to do this something like this with a key in a hash? Thanks!
Hashes aren't usually treated as ordered structures, they simply have a list of keys and values corresponding to those keys.
It's true that in Ruby hashes are technically ordered, but there's very rarely an actual use case for treating them as such.
If what you want to do is find the key corresponding to a value in a hash, you can simply use the Hash#key method:
hash = { a: 1, b: 2 }
hash.key(1) # => :a
I suppose you could use hash.keys.index(hash.key(1)) to get 0 since it's the first value, but again, I wouldn't advise doing this because it's not typical use of the data structure
There are at least a couple ways you can get this information, the 2 that come to mind are Enumerable's find_index method to pass each element to a block and check for your key:
hash.find_index { |key, _| key == 'Done' }
or you could get all the keys from your hash as an array and then look up the index as you've been doing:
hash.keys.index('Done')
I am new to ruby and don't have much experience with hashes, I have a variable named tweets and it is a hash as such:
{"statuses"=>[{"metadata"=>{"result_type"=>"recent", "iso_language_code"=>"tl"}, "lang"=>"tl"}]}
I would like to save the array of information as a separate variable in an array. How would I go about this?
Hash's have 2 very nice methods,
hash.values
hash.keys
in your case -
h = {"statuses"=>[{"metadata"=>{"result_type"=>"recent", "iso_language_code"=>"tl"}, "lang"=>"tl"}]}
p h.values
p.keys
These output arrays of each type. This might be what you want.
Also, this question will very well be closed. 1 Google search reported several Hash to Array SO questions.
Ruby Hash to array of values
Converting Ruby hashes to arrays
If you have a Hash like so:
hash = {:numbers => [1,2,3,4]}
And you need to capture the array into a new variable. You can just access the key and assign it to a new variable like so:
one_to_five = hash[:numbers]
However, note that the new variable actually holds the array that is in the hash. So altering the hash's array alters the new variable's array.
hash[:numbers] << 6
puts one_to_five #=> [1,2,3,4,5,6]
If you use dup, it will create a copy of the array so it will be two separate arrays.
one_to_five = hash[:numbers].dup
hash[:numbers] << 6
puts one_to_five #=> [1,2,3,4,5]
So, in your case:
hash = {'statuses' => [{"metadata"=>{"result_type"=>"recent", "iso_language_code"=>"tl"}, "lang"=>"tl"}]}
new_array = hash['statuses'].dup
However, it would be interesting to see what it is you are wishing to accomplish with your code, or at least get a little more context, because this may not be the best approach for your final goal. There are a great many things you can do with Arrays and Hashes (and Enumerable) and I would encourage you to read through the documentation on them.
Is there a hash implementation around that doens't remember key values? I have to make a giant hash but I don't care what the keys are.
Edit:
Ruby's hash implementation stores the key's value. I would like hash that doesn't remember the key's value. It just uses the hash function to store your value and forgets the key. The reason for this is that I need to make a hash for about 5 gb of data and I don't care what the key values are after creating it. I only want to be able to look up the values based on other keys.
Edit Edit:
The language is kind of confusing. By key's value I mean this:
hsh['value'] = data
I don't care what 'value' is after the hash function stores data in the hash.
Edit^3:
Okay so here's what I am doing: I am generating every 35-letter (nucleotide) kmer for a set of multiple genes. Each gene has an ID. The hash looks like this:
kmers = { 'A...G' => [1, 5, 3], 'G...T' => [4, 9, 9, 3] }
So the hash key is the kmer, and the value is an array containing IDs for the gene(s)/string(s) that have that kmer.
I am querying the hash for kmers in another dataset to quickly find matching genes. I don't care what the hash keys are, I just need to get the array of numbers from a kmer.
>> kmers['A...G']
=> [1, 5, 3]
>> kmers.keys.first
=> "Sorry Dave, I can't do that"
I guess you want a set, allthough it stores unique keys and no values. It has the fast lookup time from a hash.
Set is included in the standard libtrary.
require 'set'
s = Set.new
s << 'aaa'
p s.merge(['ccc', 'ddd']) #=> #<Set: {"aaa", "ccc", "ddd"}>
Even if there was an oddball hash that just recorded existence (which is how I understand the question) you probably wouldn't want to use it, as the built-in Hash would be simpler, faster, not require a gem, etc. So just set...
h[k] = k
...and call it a day...
I assume the 5 gb string is a genome, and the kmers are 35 base pair nucleotide sequences.
What I'd probably do (slightly simplified) is:
human_genome = File.read("human_genome.txt")
human_kmers = Set.new
human_genome.each_cons(35) do |potential_kmer|
human_kmers << potential_kmer unless human_kmers.include?(potential_kmer)
end
unknown_gene = File.read("unknown_gene.txt")
related_to_humans = unknown_gene.each_cons(35).any? do |unknown_gene_kmer|
human_kmers.include?(unknown_gene_kmer)
end
I have to make a giant hash but I don't care what the keys are.
That is called an array. Just use an array. A hash without keys is not a hash at all and loses its value. If you don't need key-value lookup then you don't need a hash.
Use an Array. An Array indexes by integers instead of keys. http://www.ruby-doc.org/core/classes/Array.html
a = []
a << "hello"
puts a #=> ["hello"]
How would you go about removing duplicates based on the key?
values = [{"a"=>"1"}, {"a"=>"2"}, {"b"=>"1"}, {"a"=>"4"}]
How can I ignore the value and run uniq based on key so that it returns:
[{'a' => '1'}, {'b' => '1'}]
Assuming you don't care which value gets clobbered, just run them into a hash (which does have unique keys and is therefore probably the right collection class for this case):
h = {}
values.each{|i|i.each{|k,v|h[k] = v}}
puts h # => {"a"=>"4", "b"=>"1"}
... or if you want the first of each key:
h = {}
values.each{|i|i.each{|k,v|h[k] = v unless h[k]}}
If you want to get back to a Array:
h.each{|k,v|a << {k=>v}}
The following will work only in ruby 1.9, so it might be useless.
Hash[values.map(&:first).reverse].map{|a| Hash[*a]}
If you need it in the original order,
values & Hash[values.map(&:first).reverse].map{|a| Hash[*a]}
Without introducing any intermediate variables the following 1 liner will do the trick:
> [{"a"=>"1"}, {"a"=>"2"}, {"b"=>"1"}, {"a"=>"4"}].inject({}) {|s,h| s.merge(h) unless s.keys.include? h.keys}.inject([]) {|s,h| s << {h[0]=>h[1]}}
=> [{"a"=>"4"}, {"b"=>"1"}]