Скачать или смотреть Subtract the previous number when another row is not NA in R

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This is a simplified data example.
df - data.frame(
SU = c(1, 1, NA, NA, NA, NA),
TIME = c(10, 20, 30, 40, 50, 60),
AMT = c(5, 5, NA, NA, 5, 5)
)

df - data.frame(
SU = c(1, 1, NA, NA, NA, NA),
TIME = c(10, 20, 30, 40, 50, 60),
AMT = c(5, 5, NA, NA, 5, 5)
)

I want to generate a new column TFDS, if is.na(SU) == TRUE, using TIME subtract previous AMT not NA row's TIME.
This is what I want.



SU
TIME
AMT
TFDS




1
10
5
NA


1
20
5
NA


NA
30
NA
10


NA
40
NA
20


NA
50
5
30


NA
60
5
10






SU
TIME
AMT
TFDS




1
10
5
NA


1
20
5
NA


NA
30
NA
10


NA
40
NA
20


NA
50
5
30


NA
60
5
10





SU
TIME
AMT
TFDS



SU
TIME
AMT
TFDS

SU
TIME
AMT
TFDS


1
10
5
NA


1
20
5
NA


NA
30
NA
10


NA
40
NA
20


NA
50
5
30


NA
60
5
10



1
10
5
NA

1
10
5
NA

1
20
5
NA

1
20
5
NA

NA
30
NA
10

NA
30
NA
10

NA
40
NA
20

NA
40
NA
20

NA
50
5
30

NA
50
5
30

NA
60
5
10

NA
60
5
10
I tried dplyr::lag(), but the output was not what I want.
dplyr::lag()
library(dplyr)

df - df |
mutate(
TFDS = if_else(
is.na(SU) == TRUE, TIME - lag(TIME)[!is.na(AMT)], NA
))

library(dplyr)

df - df |
mutate(
TFDS = if_else(
is.na(SU) == TRUE, TIME - lag(TIME)[!is.na(AMT)], NA
))

I believe dplyr::lag() should be used there, but how to set [!is.na(AMT)]?
dplyr::lag()
[!is.na(AMT)]


Tags: r,dplyrSource of the question:
https://stackoverflow.com/questions/7...

Question and source license information:
https://meta.stackexchange.com/help/l...
https://stackoverflow.com/