R choose组合

本文转载自：https://www.cnblogs.com/hider/p/10019220.html

总结

组合数：choose(n,k) —— 从n个中选出k个

阶乘：factorial(k) —— k!

排列数：choose(n,k) * factorial(k)

幂：^

余数：%%

整数商：%/%

列出所有组合数矩阵：combn(x,n)

t(combn(x,n)) 转置

二、例子

choose(5,3) # 10
factorial(5) # 120
choose(5,3)*factorial(3) # 60
2^10 # 1024
10 %% 3 # 1
10 %/% 3 # 3

x <- 1:5
n <-3
combn(x,n)
/*
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]    1    1    1    1    1    1    2    2    2     3
[2,]    2    2    2    3    3    4    3    3    4     4
[3,]    3    4    5    4    5    5    4    5    5     5
*/

x <- 1:5
n <-3
combn(x,n)
/*
[,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
[1,]    1    1    1    1    1    1    2    2    2     3
[2,]    2    2    2    3    3    4    3    3    4     4
[3,]    3    4    5    4    5    5    4    5    5     5
*/