我有一个数据帧，看起来像这样：
| a | b |
|---|---|
| 1 | 1 |
| 2 | 2 |
| 3 | 3 |
| 4 | 4 |
| 5 | 5 |
您可以使用一堆if/else:
f <- function(n, data){
if(n == 1){
data.frame(a = head(data[1], n),
b = head(data[2], n)) |>
transform(result = a + b)
}
else{
if(n == nrow(data)) n <- 1
data.frame(a = head(data[1], n),
b = tail(data[2], n)) |>
transform(result = a + b)
}
}
输出
lapply(vec, f, data = w)
[[1]]
a b result
1 1 1 2
[[2]]
a b result
1 1 4 5
2 2 5 7
[[3]]
a b result
1 1 3 4
2 2 4 6
3 3 5 8
[[4]]
a b result
1 1 2 3
2 2 3 5
3 3 4 7
4 4 5 9
[[5]]
a b result
1 1 5 6
您可以使用ifelse函数，它对我来说总是比ifelse指令更简单。试试这个它会起作用：
library(tidyverse)
a = seq(1,5,1)
b = seq(1,5,1)
w = tibble(a,b)
im = function(mat,window){
SA = unlist(#unlist to transform list type result of ifelse to vector
ifelse(
# here is the condition
window==nrow(mat),
# if condition is TRUE return first element
mat%>%
dplyr::select(1)%>%
dplyr::slice_head(n=1),
# if condition is FALSE return first window elements
mat%>%
dplyr::select(1)%>%
dplyr::slice_head(n=window))
)
SB = unlist(
ifelse(window==nrow(mat),
mat%>%
dplyr::select(2)%>%
dplyr::slice_tail(n=1),
mat%>%
dplyr::select(2)%>%
dplyr::slice_tail(n=window))
)
margin = min(SA+SB)
return(margin)
}
im(w,5)