R 对列的前导X行求和？

我有一个代码，其中我对值的前导行进行检查，以计算覆盖率值。我有以下代码示例：

library(data.table)

df <- data.frame(
  dept = c(rep('FIREDEPT', 5), rep('WATERDEPT', 5)),
  month = 201808:201812,
  initial_stock = sample(75884:85347, 10),
  variable_predicted = sample(50000:100000, 10))


df <- mutate(df, calculation = ifelse(initial_stock <= (shift(variable_predicted, type="lead", fill = 0)
                                                        + shift(variable_predicted, type="lead", fill = 0, n = 2)
                                                        + shift(variable_predicted, type="lead", fill = 0, n = 3)),
                                      (3 + (initial_stock 
                                            - shift(variable_predicted, type="lead", fill = 0) 
                                            - shift(variable_predicted, type="lead", fill = 0, n = 2)
                                      ) / shift(variable_predicted, type="lead", fill = 0, n = 3)) * 30,
                                      0)) 

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在不使用一系列移位的情况下？

shift

是矢量化的，因此您可以给它一个

n

的向量，然后将结果与

Reduce（“+”，…）

---

非常感谢。我对Reduce不熟悉。

(shift(variable_predicted, type="lead", fill = 0)
  + shift(variable_predicted, type="lead", fill = 0, n = 2)
  + shift(variable_predicted, type="lead", fill = 0, n = 3)),

a <- 
with(df,
     (shift(variable_predicted, type="lead", fill = 0)
  + shift(variable_predicted, type="lead", fill = 0, n = 2)
  + shift(variable_predicted, type="lead", fill = 0, n = 3)))

b <- 
with(df,
     Reduce(`+`, shift(variable_predicted, n = 1:3, fill = 0, type = 'lead')))


identical(a, b)
# [1] TRUE

library(zoo)
d <- 
with(df, 
  rollsum(c(variable_predicted[-1], rep(0, 3)), 3))

all.equal(a, d)
# [1] TRUE