r - 移动均值作为 dplyr 中的函数

Question

我想创建一个函数来计算可变数量的最后观测值和不同变量的移动平均值。以此作为模拟数据:

df = expand.grid(site = factor(seq(10)),
                 year = 2000:2004,
                 day = 1:50)
df$temp = rpois(dim(df)[1], 5) 

计算 1 个变量和固定数量的最后观察值有效。例如。这将计算过去 5 天的平均温度:

library(dplyr)
library(zoo)

df <- df %>% 
            group_by(site, year) %>% 
                arrange(site, year, day) %>% 
                      mutate(almost_avg = rollmean(x = temp, 5, align = "right", fill = NA)) %>%
                          mutate(avg = lag(almost_avg, 1))

到目前为止一切顺利。现在尝试功能化失败了。

avg_last_x <- function(dataframe, column, last_x) {

  dataframe <- dataframe %>% 
    group_by(site, year) %>% 
      arrange(site, year, day) %>% 
        mutate(almost_avg = rollmean(x = column, k = last_x, align = "right", fill = NA)) %>%
          mutate(avg = lag(almost_avg, 1))

  return(dataframe) }

avg_last_x(dataframe = df, column = "temp", last_x = 10)

我收到这个错误:

Error in mutate_impl(.data, dots) : k <= n is not TRUE 

我知道这可能与 evaluation mechanism in dplyr 有关，但我没有修好它。

预先感谢您的帮助。

Answer 1

这应该可以解决它。

library(lazyeval)

avg_last_x <- function(dataframe, column, last_x) {
  dataframe %>% 
    group_by(site, year) %>% 
    arrange(site, year, day) %>% 
    mutate_(almost_avg = interp(~rollmean(x = c, k = last_x, align = "right", 
                                          fill = NA), c = as.name(column)),
            avg = ~lag(almost_avg, 1))
}