在向量中查找重复值的元素对 - R

Question

我有一个带有一些重复元素的向量。我想列出所有具有相同值的索引对。

即。给定输入

x <- c(1,2,3,2,4,3,2)

我想生成列表

duplicate_x <- [[2,4,7],[3,6]]

如何在R

中解决这个问题

Answer 1

<input>

Answer 2

你也可以这样做：

dupEle <- unique(x[duplicated(x)])
lapply(dupEle, function(ele) which(x == ele))
[[1]]
[1] 2 4 7

[[2]]
[1] 3 6

Answer 3

我对建议的两种解决方案进行了速度测试。

find_dups = function(x) {
  dups = duplicated(x) | duplicated(x, fromLast = T)

  split(which(dups), x[dups])
}
find_dups2 = function(x) {
  dupEle <- unique(x[duplicated(x)])
  lapply(dupEle, function(ele) which(x == ele))
}

dups_small = c(1,2,3,2,4,3,2)
set.seed(1)
dups_large = sample(0:9, size = 50, replace = T)

结果：

> microbenchmark::microbenchmark(find_dups(dups_small),
+                                find_dups2(dups_small))
Unit: microseconds
                   expr    min     lq     mean median      uq     max neval cld
  find_dups(dups_small) 53.833 55.589 69.43074 57.491 66.4140 288.183   100   b
 find_dups2(dups_small) 13.166 15.215 28.82765 16.677 20.0415 523.119   100  a 

> microbenchmark::microbenchmark(find_dups(dups_large),
+                                find_dups2(dups_large))
Unit: microseconds
                   expr    min     lq     mean median      uq     max neval cld
  find_dups(dups_large) 50.615 52.079 59.88706 53.834 64.9515 149.212   100   b
 find_dups2(dups_large) 25.747 28.965 37.14842 31.014 34.3780 289.354   100  a 

因此，重复劳拉解决方案实际上要快得多，大约在2到3.5倍之间。