Question

我想将循环中的矢量结果存储到矩阵中，但我不知道行数。例如，以下代码将说明我想要做的事情：

result_final <- c()
for (i in 1:5){
   n <- sample(1:5,1) #get the number of rows for this iteration
   result_this_time <- matrix(0,n,3) #generate a matrix with row number 
                                     #are unknown before running the iteration
   #combine all the results from each iteration together 
   if (i == 1) result_final <- result_this_time
       else result_final <- rbind(result_final,result_this_time)
    }
result_final

以上代码适合我。问题是它有点复杂。如您所见，当我使用c()生成新向量时，我不必指示向量的长度。代码test1 <- c();test1[3]<-1不会报告任何错误，但代码test2 <- matrix();test2[3,3]<-1会报错，因为它引用了错误的下标。所以我想知道无论如何我可以创建一个“矩阵”，我没有必要明确指出矩阵行（就像使用c()创建一个向量）来摆脱{{1}声明。

Answer 1

我使用lapply()。外部lapply()控制整体重复，而内部lapply()执行n指定的行数。 do.call()用于简化和绑定（rbind()）元素。与下面的原始代码进行比较。

set.seed(1237)
# outer loop controls overall repetition
do.call(rbind, lapply(1:5, function(x) {
  n <- sample(1:5, 1)
  # inner loop control individual rows by n
  do.call(rbind, lapply(1:n, function(y) rbind(rep(0, 3))))
}))
[,1] [,2] [,3]
[1,]    0    0    0
[2,]    0    0    0
[3,]    0    0    0
[4,]    0    0    0
[5,]    0    0    0
[6,]    0    0    0
[7,]    0    0    0
[8,]    0    0    0
[9,]    0    0    0
[10,]    0    0    0

set.seed(1237)
result_final <- c()
for (i in 1:5){
  n <- sample(1:5,1) #get the number of rows for this iteration
  result_this_time <- matrix(0,n,3) #generate a matrix with row number 
  #are unknown before running the iteration
  #combine all the results from each iteration together 
  if (i == 1) result_final <- result_this_time
  else result_final <- rbind(result_final,result_this_time)
}
result_final
[,1] [,2] [,3]
[1,]    0    0    0
[2,]    0    0    0
[3,]    0    0    0
[4,]    0    0    0
[5,]    0    0    0
[6,]    0    0    0
[7,]    0    0    0
[8,]    0    0    0
[9,]    0    0    0
[10,]    0    0    0

当R中未知的维度时，将矢量结果从循环存储到矩阵中

1 个答案: