r - 如何计算表中的共现率？

Question

我有一个简单的矩阵，例如

test <- matrix(c("u1","p1","u1","p2","u2","p2","u2",
                 "p3","u3","p1","u4","p2","u5","p1",
                 "u5","p3","u6","p3","u7","p4","u7",
                 "p3","u8","p1","u9","p4"),
               ncol=2,byrow=TRUE) 
colnames(test) <- c("user","product")
test1<-as.data.frame(test)

测试:

   user   product
1  u1      p1
2  u1      p2
3  u2      p2 
4  u2      p3
5  u3      p1
6  u4      p2
7  u5      p1
8  u5      p3
9  u6      p3
10 u7      p4
11 u7      p3
12 u8      p1
13 u9      p4

我想统计有多少用户同时购买了产品对，例如p1&p2、p2&p3...

table(test1$product,test1$product)给我这个:

     p1   p2  p3  p4
 p1   4   0   0   0
 p2   0   3   0   0
 p3   0   0   4   0
 p4   0   0   0   2

我怎样才能得到正确的结果:

     p1   p2  p3  p4
 p1   4   1   1   0
 p2   1   3   1   0
 p3   1   1   4   1
 p4   0   0   1   2

Answer 1

查看所需的输出，您正在寻找 crossprod 函数:

crossprod(table(test1))
#        product
# product p1 p2 p3 p4
#      p1  4  1  1  0
#      p2  1  3  1  0
#      p3  1  1  4  1
#      p4  0  0  1  2

这与 crossprod(table(test1$user, test1$product)) 相同(反射(reflect) Dennis 的评论)。