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Roll ? ?.  0 0 0 Deal

? y yields a uniform random selection from the population i.y if y is a positive integer, or from the interval of numbers greater than or equal to 0 and less than 1, if y is 0. The random seed used begins at 7^5 (16807).
 
  x ? y is a list of x items randomly chosen without repetition from i.y .
 

The corresponding use of ?. proceeds from a fixed random seed of 7^5 and has no effect on the results of ? (monad or dyad). Use of the fixed seed function ?. makes examples reproducible:
   ?. 6 
0
                
   ?. 6 6 6 6 6 6 6 6
0 5 5 4 2 3 2 1

   6 ?. 6                     A random permutation
0 1 5 4 3 2

   mean=: +/ % #
   mean ?. 1000 # 6
2.459

   ] m=: ?. 4 4 $ 9           A random matrix for experimentation
3 8 8 4
2 0 2 7
4 2 3 5
1 1 7 2
          
   -/ . * m                   The determinant of m
_659

   f=: ?.@$ % ] - 1:
   3 6 f 9                    Random 3 by 6 table in range zero to one with resolution 9
0.375     1     1  0.5  0.25     0
 0.25 0.875   0.5 0.25 0.375 0.625
0.125 0.125 0.875 0.25 0.875  0.75
The random seed (a beginning value for the pseudo-random number generator) is set by the foreign conjunction using 9!:1, and queried with 9!:0 . The algorithm is GB_Flip (Knuth [15]) with a period length of at least _1+2^55 .


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