I have a vector of length 100 and I want to get a sample of certain size like 50, from all permutations of length 20 from elements of my original vector
My attempt so far is to first to get all permutations then select a sample of size 50
First part
All_Permutation = gtools::permutations(n = 100, r = 20, v = 1:100)
Second part
I could not complete because, the first part is taking considerable amount of time and memory
I wonder is there any more manageable way to get that sample?
Try RcppAlgos::permuteSample.
> RcppAlgos::permuteSample(v=1:100, m=20, n=50, seed=42)
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10] [,11] [,12] [,13] [,14] [,15] [,16] [,17] [,18] [,19] [,20]
[1,] 13 87 36 100 62 58 30 64 49 72 57 2 28 17 41 88 40 85 65 76
[2,] 45 12 27 18 69 57 52 26 3 29 63 17 11 82 70 50 75 78 38 6
[3,] 49 11 81 92 15 65 78 67 93 62 46 33 25 73 83 10 57 38 41 56
[4,] 60 97 72 4 35 19 22 66 37 100 61 81 34 14 40 89 11 13 3 74
[5,] 7 41 51 56 59 18 32 39 99 97 15 95 83 85 4 84 33 10 91 40
[6,] 86 43 82 12 33 36 41 96 81 63 26 34 17 4 69 10 53 59 76 71
...
You can also calculate the number of permutations:
> RcppAlgos::permuteCount(v=1:100, m=20)
Big Integer ('bigz') :
[1] 1303995018204712451095685346159820800000