Ruby - return an array in random order
What is th开发者_StackOverflow社区e easiest way to return an array in random order in Ruby? Anything that is nice and short that can be used in an IRB session like
[1,2,3,4,5].random()
# or
random_sort([1,2,3,4,5])
array.shuffle
If you don't have [].shuffle, [].sort_by{rand} works as pointed out by sepp2k. .sort_by temporarily replaces each element by something for the purpose of sorting, in this case, a random number.
[].sort{rand-0.5} however, won't properly shuffle. Some languages (e.g. some Javascript implementations) don't properly shuffle arrays if you do a random sort on the array, with sometimes rather public consequences.
JS Analysis (with graphs!): http://www.robweir.com/blog/2010/02/microsoft-random-browser-ballot.html
Ruby is no different! It has the same problem. :)
#sort a bunch of small arrays by rand-0.5
a=[]
100000.times{a << [0,1,2,3,4].sort{rand-0.5}}
#count how many times each number occurs in each position
b=[]
a.each do |x|
x.each_index do |i|
b[i] ||=[]
b[i][x[i]] ||= 0
b[i][x[i]] += 1
end
end
p b
=>
[[22336, 18872, 14814, 21645, 22333],
[17827, 25005, 20418, 18932, 17818],
[19665, 15726, 29575, 15522, 19512],
[18075, 18785, 20283, 24931, 17926],
[22097, 21612, 14910, 18970, 22411]]
Each element should occur in each position about 20000 times. [].sort_by(rand) gives much better results.
#sort with elements first mapped to random numbers
a=[]
100000.times{a << [0,1,2,3,4].sort_by{rand}}
#count how many times each number occurs in each position
...
=>
[[19913, 20074, 20148, 19974, 19891],
[19975, 19918, 20024, 20030, 20053],
[20028, 20061, 19914, 20088, 19909],
[20099, 19882, 19871, 19965, 20183],
[19985, 20065, 20043, 19943, 19964]]
Similarly for [].shuffle (which is probably fastest)
[[20011, 19881, 20222, 19961, 19925],
[19966, 20199, 20015, 19880, 19940],
[20062, 19894, 20065, 19965, 20014],
[19970, 20064, 19851, 20043, 20072],
[19991, 19962, 19847, 20151, 20049]]
What about this?
Helper methods for Enumerable, Array, Hash, and String that let you pick a random item or shuffle the order of items.
http://raa.ruby-lang.org/project/rand/
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