Is there an equivalent to `Array::sample` for hash

问题:

I'm looking to extract n random key-value pairs from a hash.

回答1:

Hash[original_hash.to_a.sample(n)]

For Ruby 2.1,

original_hash.to_a.sample(n).to_h

回答2:

I don't know of such method. Still you can do something like:

h[h.keys.sample]

If you need to sample more than one element the code will have to be a bit more complicated.

EDIT: to get key value pairs instead of only the value you can do something like:

keys_sample = h.keys.sample(n)
keys_sample.zip(keys_sample.map{|k| h[k])

回答3:

If your sample has only one element, you could use this:

sample = h.keys.sample
h.select { |k,v| k == sample }

Or if your sample contains more than one element, use this:

n = 2
sample = h.keys.sample(n)
h.select { |k,v| sample.include?(k) }

回答4:

Reading the top ranked answers, I'd go with it depends:

1. If you want to sample only one element from the hash, @Ivaylo Strandjev's solution only relies on hash lookup and Array#sample:

   hsh[hsh.keys.sample]
   

2. To sample multiple hash elements, @sawa's answer leverages Array#to_h:

   hsh.to_a.sample(n).to_h
   

---

Note that, as @cadlac mentions, hsh.to_a.sample.to_h won't work as expected. It will raise

TypeError: wrong element type String at 0 (expected array)

because Array#sample in this case returns just the element array, and not the array containing the element array.

A workaround is his solution, providing an n = 1 as an argument:

hsh.to_a.sample(1).to_h

---

PS: not looking for upvotes, only adding it as an explanation for people newer to Ruby.

回答5:

One way to accomplish this:

rank_hash = {"Listen" => 1, "Download" => 60, "Share" => 150, "Purchase" => 700 }

rank_array = rank_hash.to_a

Than call this to get random array sample of the k/v pair:

rank_array[rand(0..3)]

or this to not hard-code the arrays length:

rank_array[rand(0..(rank_array.length) -1)]

Example:

["Download", 60]