[英]How to add lag and lead to each observations for more variables excluding NAs within data.table?
I have a data.table similar to this: 我有一个类似这样的data.table:
library(data.table)
mydt <- data.table(id = LETTERS[1:6], x = 1:6, y = 2:3)
> mydt
id x y
1: A 1 2
2: B 2 3
3: C 3 2
4: D 4 3
5: E 5 2
6: F 6 3
I would like to replace the value columns with adding the lag and lead to each observation (ie x[-1] + x + x[1]
). 我想替换值列,添加滞后并导致每个观察(即
x[-1] + x + x[1]
)。 I can do something like this with the amazing shift()
feature. 我可以使用惊人的
shift()
功能做这样的事情。
cols <- c('x', 'y')
mydt[
,
(cols) := shift(.SD, 1) + .SD + shift(.SD, 1, type = 'lead'),
.SDcols = cols
][]
id x y
1: A NA NA
2: B 6 7
3: C 9 8
4: D 12 7
5: E 15 8
6: F NA NA
But this introduces NAs for rows where there is no lead/lag value. 但是这会为没有超前/滞后值的行引入NA。 How can I modify the calculation to use the available two values only for these rows (like
na.rm = TRUE
)? 如何修改计算以仅对这些行使用可用的两个值(如
na.rm = TRUE
)? So that the output would be 这样输出就可以了
id x y
1: A 3 5
2: B 6 7
3: C 9 8
4: D 12 7
5: E 15 8
6: F 11 5
I tried using sum(..., na.rm = TRUE)
instead of the +
operator but that gives error: Error in sum(shift(.SD, 1), .SD, shift(.SD, 1, type = "lead"), na.rm = TRUE) : invalid 'type' (list) of argument
. 我尝试使用
sum(..., na.rm = TRUE)
而不是+
运算符,但这给出了错误: Error in sum(shift(.SD, 1), .SD, shift(.SD, 1, type = "lead"), na.rm = TRUE) : invalid 'type' (list) of argument
。
I also tried the following but that apparently gives something else as a result. 我也试过以下但是显然会给出其他的东西。
mydt[
,
(cols) := lapply(
.SD,
function(x) sum(shift(x, 1), x, shift(x, 1, type = 'lead'), na.rm = TRUE)
),
.SDcols = cols
][]
id x y
1: A 126 90
2: B 126 90
3: C 126 90
4: D 126 90
5: E 126 90
6: F 126 90
As @akrun and @DavidArenburg pointed out, the shift
function has a fill
parameter which solves the issue. 正如@akrun和@DavidArenburg指出的那样,
shift
函数有一个fill
参数来解决问题。
cols <- c('total_open', 'total_send')
mydt[
,
(cols) := shift(.SD, 1, fill = 0) + .SD + shift(.SD, 1, type = 'lead', fill = 0),
.SDcols = cols
][]
id x y
1: A 3 5
2: B 6 7
3: C 9 8
4: D 12 7
5: E 15 8
6: F 11 5
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