R如何使循环更快 [英] R how to make loop faster

问题描述

我有一个类似下面的代码，其中包含两个循环.该代码读取每月的流数据并将其复制为多个.循环是如此之慢.我想知道是否还有其他方法可以使其更快?

I have a code like below that contains two loops. The code reads monthly streamflow data and makes it as multi-replicate. The loops are so slow. I was wondering if there is any alternative way to make it faster?

library(xlsx)
library(data.table)

  a <- read.xlsx("streamflow.xlsx",sheetName = "Sheet1", header = TRUE)
  b=matrix(nrow=129792,ncol=17)
  b= data.frame(b)
  i=0

  for (j in -11:1236)
  {
   for (k in 1:104)
   {
    i=i+1
    j=j+12
    j[j > 1248] <-j-1248
    b[i,] <-a[j,]
   }
 }

谢谢

推荐答案

我相信这是将double for循环正确转换为矢量化代码的方法.它应该大大提高速度.另外，无需将b声明为矩阵并将其转换为data.frame，只需从a获取值即可.

I believe this is a proper translation of your double for-loop into vectorized code. It should increase the speed dramatically. Also, there is no need to declare b as a matrix and convert it to a data.frame, the values can just be obtained from a.

j_iter <- -11:1236
k_iter <- 1:104

k <- seq(12, length(k_iter) * 12, 12)
k <- rep(k, times=length(j_iter))

j <- rep(j_iter, each=length(k_iter))
j <- j + k
j[j > 1248] <- j[j > 1248] - 1248

b <- a[j,]

这篇关于R如何使循环更快的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！