“累积差异"R中的函数 [英] "Cumulative difference" function in R

问题描述

是否有预先存在的函数来计算结果值之间的累积差异?

Is there a pre-existing function to calculate the cumulative difference between consequtive values?

上下文:这是估计一个人在由 CycleStreet.net.

Context: this is to estimate the change in altitude that a person has to undergo in both directions on a journey generated by CycleStreet.net.

可重现的例子:

x <- c(27, 24, 24, 27, 28) # create the data

方法一:for循环

for(i in 2:length(x)){ # for loop way
  if(i == 2) cum_change <- 0
  cum_change <-  Mod(x[i] - x[i - 1]) + cum_change
  cum_change
}
## 7

方法二:矢量化

diffs <- Mod(x[-1] - x[-length(x)]) # vectorised way
sum(diffs)

## 7

两者似乎都有效.我只是想知道在 base R 中是否还有另一个(更通用的)实现，或者像 dplyr 或 RcppRoll.

Both seem to work. I'm just wondering if there's another (and more generalisable) implementation in base R or with something like dplyr or RcppRoll.

推荐答案

这比你现有的要短:

sum(abs(diff(x)))

它等同于您的第二个解决方案，除了使用 diff 来计算差异和 abs 而不是 Mod，因为输入是实部(无虚部).

It's equivalent to your second solution, other than using diff to compute the diffs, and abs instead of Mod, as the input is real (no imaginary component).

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