在R中找到数组中最接近元素的最快方法 [英] Quickest way to find closest elements in an array in R

问题描述

我想在R中找到斋戒的方式，以识别最接近给定Xtimes值的Ytimes数组中元素的索引.

I would like find the fastes way in R to indentify indexes of elements in Ytimes array which are closest to given Xtimes values.

到目前为止，我一直在使用一个简单的for循环，但必须有一种更好的方法:

So far I have been using a simple for-loop, but there must be a better way to do it:

Xtimes <- c(1,5,8,10,15,19,23,34,45,51,55,57,78,120)
Ytimes <- seq(0,120,length.out = 1000)

YmatchIndex = array(0,length(Xtimes))
for (i in 1:length(Xtimes)) {
  YmatchIndex[i] = which.min(abs(Ytimes - Xtimes[i]))
}

print(Ytimes[YmatchIndex])

推荐答案

R是矢量化的，因此跳过for循环.这样可以节省脚本和计算时间.只需将for循环替换为apply函数.由于我们要返回一维向量，因此我们使用sapply.

R is vectorized, so skip the for loop. This saves time in scripting and computation. Simply replace the for loop with an apply function. Since we're returning a 1D vector, we use sapply.

YmatchIndex <- sapply(Xtimes, function(x){which.min(abs(Ytimes - x))})

证明apply更快:

library(microbenchmark)
library(ggplot2)

# set up data
Xtimes <- c(1,5,8,10,15,19,23,34,45,51,55,57,78,120)
Ytimes <- seq(0,120,length.out = 1000)

# time it
mbm <- microbenchmark(
  for_loop = for (i in 1:length(Xtimes)) {
    YmatchIndex[i] = which.min(abs(Ytimes - Xtimes[i]))
  },
  apply    = sapply(Xtimes, function(x){which.min(abs(Ytimes - x))}),
  times = 100
)

# plot
autoplot(mbm)

请参见?apply for more.

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