我试着用R来计算矩阵中一系列值的移动平均值。R中似乎没有一个内置函数可以让我计算移动平均线。有任何软件包提供这样的服务吗?还是需要我自己写?
当前回答
事实上，RcppRoll非常好。
cantdutchthis发布的代码必须在窗口的第四行进行修正:
ma <- function(arr, n=15){
res = arr
for(i in n:length(arr)){
res[i] = mean(arr[(i-n+1):i])
}
res
}
这里给出了另一种处理缺失的方法。
第三种方法，改进cantdutch这段代码来计算部分平均与否，如下:
ma <- function(x, n=2,parcial=TRUE){
res = x #set the first values
if (parcial==TRUE){
for(i in 1:length(x)){
t<-max(i-n+1,1)
res[i] = mean(x[t:i])
}
res
}else{
for(i in 1:length(x)){
t<-max(i-n+1,1)
res[i] = mean(x[t:i])
}
res[-c(seq(1,n-1,1))] #remove the n-1 first,i.e., res[c(-3,-4,...)]
}
}
其他回答
您可以使用RcppRoll来实现用c++编写的快速移动平均线。只需调用roll_mean函数。文档可以在这里找到。
否则，这个(较慢的)for循环应该可以做到:
ma <- function(arr, n=15){
res = arr
for(i in n:length(arr)){
res[i] = mean(arr[(i-n):i])
}
res
}
事实上，RcppRoll非常好。
cantdutchthis发布的代码必须在窗口的第四行进行修正:
ma <- function(arr, n=15){
res = arr
for(i in n:length(arr)){
res[i] = mean(arr[(i-n+1):i])
}
res
}
这里给出了另一种处理缺失的方法。
第三种方法，改进cantdutch这段代码来计算部分平均与否，如下:
ma <- function(x, n=2,parcial=TRUE){
res = x #set the first values
if (parcial==TRUE){
for(i in 1:length(x)){
t<-max(i-n+1,1)
res[i] = mean(x[t:i])
}
res
}else{
for(i in 1:length(x)){
t<-max(i-n+1,1)
res[i] = mean(x[t:i])
}
res[-c(seq(1,n-1,1))] #remove the n-1 first,i.e., res[c(-3,-4,...)]
}
}
下面的示例代码展示了如何使用zoo包中的rollmean函数计算居中移动平均和尾随移动平均。
library(tidyverse)
library(zoo)
some_data = tibble(day = 1:10)
# cma = centered moving average
# tma = trailing moving average
some_data = some_data %>%
mutate(cma = rollmean(day, k = 3, fill = NA)) %>%
mutate(tma = rollmean(day, k = 3, fill = NA, align = "right"))
some_data
#> # A tibble: 10 x 3
#> day cma tma
#> <int> <dbl> <dbl>
#> 1 1 NA NA
#> 2 2 2 NA
#> 3 3 3 2
#> 4 4 4 3
#> 5 5 5 4
#> 6 6 6 5
#> 7 7 7 6
#> 8 8 8 7
#> 9 9 9 8
#> 10 10 NA 9
vector_avg <- function(x){
sum_x = 0
for(i in 1:length(x)){
if(!is.na(x[i]))
sum_x = sum_x + x[i]
}
return(sum_x/length(x))
}
编辑:非常喜欢添加侧参数，例如，一个日期向量的过去7天的移动平均值(或总和，或…)。
对于那些只想自己计算的人来说，它无非是:
# x = vector with numeric data
# w = window length
y <- numeric(length = length(x))
for (i in seq_len(length(x))) {
ind <- c((i - floor(w / 2)):(i + floor(w / 2)))
ind <- ind[ind %in% seq_len(length(x))]
y[i] <- mean(x[ind])
}
y
但是让它独立于mean()会很有趣，所以你可以计算任何“移动”函数!
# our working horse:
moving_fn <- function(x, w, fun, ...) {
# x = vector with numeric data
# w = window length
# fun = function to apply
# side = side to take, (c)entre, (l)eft or (r)ight
# ... = parameters passed on to 'fun'
y <- numeric(length(x))
for (i in seq_len(length(x))) {
if (side %in% c("c", "centre", "center")) {
ind <- c((i - floor(w / 2)):(i + floor(w / 2)))
} else if (side %in% c("l", "left")) {
ind <- c((i - floor(w) + 1):i)
} else if (side %in% c("r", "right")) {
ind <- c(i:(i + floor(w) - 1))
} else {
stop("'side' must be one of 'centre', 'left', 'right'", call. = FALSE)
}
ind <- ind[ind %in% seq_len(length(x))]
y[i] <- fun(x[ind], ...)
}
y
}
# and now any variation you can think of!
moving_average <- function(x, w = 5, side = "centre", na.rm = FALSE) {
moving_fn(x = x, w = w, fun = mean, side = side, na.rm = na.rm)
}
moving_sum <- function(x, w = 5, side = "centre", na.rm = FALSE) {
moving_fn(x = x, w = w, fun = sum, side = side, na.rm = na.rm)
}
moving_maximum <- function(x, w = 5, side = "centre", na.rm = FALSE) {
moving_fn(x = x, w = w, fun = max, side = side, na.rm = na.rm)
}
moving_median <- function(x, w = 5, side = "centre", na.rm = FALSE) {
moving_fn(x = x, w = w, fun = median, side = side, na.rm = na.rm)
}
moving_Q1 <- function(x, w = 5, side = "centre", na.rm = FALSE) {
moving_fn(x = x, w = w, fun = quantile, side = side, na.rm = na.rm, 0.25)
}
moving_Q3 <- function(x, w = 5, side = "centre", na.rm = FALSE) {
moving_fn(x = x, w = w, fun = quantile, side = side, na.rm = na.rm, 0.75)
}
