r-查找列表元素的交集长度

Question

有没有一种更快、更干净的方法可以从x中获取y？

x <- list(c("a", "b", "c", "d"), 
c("a", "b", "e"), 
c("x", "y"),
c("z", "x"))
y <- vector(mode = "list", length = length(x))
for(i in 1:length(x)){
for(j in 1:length(x)){
    y[[i]] <- append(y[[i]], length(intersect(x[[i]], x[[j]])))}}
y <- do.call(rbind, y)  

Answer 1

un <- unique(unlist(x))
crossprod(sapply(x,function(y)un%in%y))
#      [,1] [,2] [,3] [,4]
# [1,]    4    2    0    0
# [2,]    2    3    0    0
# [3,]    0    0    2    1
# [4,]    0    0    1    2

microbenchmark::microbenchmark(user1389960(), times = 1000)
# Unit: microseconds
#           expr     min       lq    mean   median      uq      max neval
#  user1389960() 172.631 181.5195 243.918 187.1015 198.716 45083.95  1000
microbenchmark::microbenchmark(eipi10(), times = 1000)
# Unit: microseconds
#      expr     min       lq     mean  median       uq      max neval
#  eipi10() 218.625 225.9635 246.9797 234.469 245.4545 1175.439  1000
microbenchmark::microbenchmark(Julius(), times = 1000)
# Unit: microseconds
#      expr    min     lq     mean  median     uq      max neval
#  Julius() 30.322 32.511 37.61541 34.0175 37.957 1026.268  1000
microbenchmark::microbenchmark(ColonelBeauvel(), times = 1000)
# Unit: microseconds
#              expr     min      lq     mean  median      uq      max neval
#  ColonelBeauvel() 162.103 169.548 183.9076 175.683 183.677 1052.435  1000

Answer 2

这更干净，但不是更快：

sapply(x, function(a) {
  sapply(x, function(b) length(intersect(a,b)))
})

时间安排：

microbenchmark::microbenchmark(sapply(x, function(a) {
  sapply(x, function(b) length(intersect(a,b)))}))
    min       lq     mean  median     uq     max neval
377.513 392.2505 406.1243 404.318 416.22 511.877   100
microbenchmark::microbenchmark(for(i in 1:length(x)){
  for(j in 1:length(x)){
    y[[i]] <- append(y[[i]], length(intersect(x[[i]], x[[j]])))}})   
    min       lq     mean  median     uq      max neval
350.471 375.7305 422.0248 388.695 414.41 2386.736   100

Answer 3

我会使用mapply:

n = length(x)
matrix(mapply(function(u,v) length(intersect(u,v)), rep(x, n), rep(x, each=n)), ncol=n)
#     [,1] [,2] [,3] [,4]
#[1,]    4    2    0    0
#[2,]    2    3    0    0
#[3,]    0    0    2    1
#[4,]    0    0    1    2