Question

有一个矩阵A，如：

 1   21    3   49   59
21   33   59   67   65
 3    5    7    8   11
21   76    5    4    9

我想只得到每行没有3个或更多数字的行，它们之间都有最大差异＆lt; 10

此函数应仅返回第1行。

Answer 1

这段代码可以。还有一个小例子：

vec <- c(1, 21, 3, 49, 59, 21, 33, 59,
         67, 65, 3, 5, 7, 8, 11, 21, 76, 5, 4, 9)

A <- matrix(vec, nrow = 4, byrow = TRUE)

returnRows <- function(x) {
  count <- 0
  for (i in 1:nrow(x)) {
    if (length(which(diff(combn(x[i,],2)) < 10)) < 3) {
      count <- c(count,i)
    }
  }
  return(x[count[-1],])
}

## example

returnRows(A)

Answer 2

您查找所有值组合的diff，并使用rowSums进行过滤，即

A[rowSums(t(apply(A, 1, function(i)combn(i, 2, diff))) < 10) < 3,]
#[1]  1 21  3 49 59

Answer 3

分析两个提交的答案：

输入：

pacman::p_load(microbenchmark)

vec <- c(1, 21, 3, 49, 59, 21, 33, 59,
     67, 65, 3, 5, 7, 8, 11, 21, 76, 5, 4, 9)

A <- matrix(vec, nrow = 4, byrow = TRUE)

returnRows <- function(x) {
  count <- 0
  for (i in 1:nrow(x)) {
    if (length(which(diff(combn(x[i,],2)) < 10)) < 3) {
      count <- c(count,i)
    }
  }
  return(x[count[-1],])
}

# dvarelas' answer
microbenchmark(returnRows(A))

# Sotos' answer
microbenchmark(A[rowSums(t(apply(A, 1, function(i)combn(i, 2, diff))) < 10) < 3,])

输出：

> microbenchmark(returnRows(A))
Unit: microseconds
          expr     min      lq     mean   median       uq    max neval
 returnRows(A) 137.113 141.124 152.6586 143.8595 154.7995 301.94   100

> microbenchmark(A[rowSums(t(apply(A, 1, function(i)combn(i, 2, diff))) < 10) < 3,])
Unit: microseconds
                                                                      expr     min      lq     mean   median     uq      max neval
 A[rowSums(t(apply(A, 1, function(i) combn(i, 2, diff))) < 10) <      3, ] 374.507 431.759 645.9935 544.4395 742.45 5324.047   100

结论：dvarelas的答案要快于Sotos的答案

过滤矩阵行，其中行号之间存在最大差异

3 个答案: