R use ifelse to replicate

Question

I want to use ifelse to replicate my data.
The problem is How to use ifelse to replicate different rows, which have different conditions. Or maybe there are other solutions. data here:

type     Time          value
A        2015-01-01    100
A        2016-05-01    200
B        2015-12-01    150
B        2016-12-01    300

The result I want is like:

type     Time          value
A        2015-01-01    100
A        2015-01-01    100
A        2015-01-01    100
A        2015-01-01    100
A        2015-01-01    100
A        2015-01-01    100
A        2015-01-01    100
A        2015-01-01    100
A        2015-01-01    100
A        2015-01-01    100
A        2015-01-01    100
A        2015-01-01    100
A        2015-01-01    100
A        2016-05-01    200
A        2016-05-01    200
A        2016-05-01    200
A        2016-05-01    200
A        2016-05-01    200
A        2016-05-01    200
A        2016-05-01    200
A        2016-05-01    200
B        2015-12-01    150
B        2015-12-01    150
B        2015-12-01    150
B        2015-12-01    150
B        2015-12-01    150
B        2015-12-01    150
B        2015-12-01    150
B        2015-12-01    150
B        2015-12-01    150
B        2015-12-01    150
B        2015-12-01    150
B        2015-12-01    150
B        2015-12-01    150    
B        2016-12-01    300

My code:

library(readxl)
library(lubridate)
library(data.table)
data <- read_excel("data.xlsx")
data <- as.data.table(data)
data[,Time:=as.Date(Time,"%Y/%m/%d")]
result <- data[ifelse(year(Time)==2016,rep(1:.N,12-month(Time)+1),rep(1:.N,13))]

However, it is not the same as what I actually want.
I think the problem is I cannot use .N. Any suggestion? Thanks.

Is `.N` a variable you've declared? Or a function? Try encasing `.N` in backwards apostophes. `\`.N\`` — Oliver Frost, Apr 20 '17 at 08:17
`.N` is a special-symbol in package `data.table`. use `?.N` for more details. — Peter Chen, Apr 20 '17 at 08:20

mtoto · Accepted Answer · 2017-04-20T11:43:30.253

4

You can create a reps column based on your conditions, that will allow us to repeat each row times the value in this new variable:

library(data.table)
data[,reps:=ifelse(year(Time)==2016, 12-month(Time)+1, 13)][rep(1:.N,reps)]

Or without ifelse():

data[,reps := 13][year(Time)==2016, reps := 11-month(Time)][rep(1:.N, reps)]

edited Apr 20 '17 at 11:43

answered Apr 20 '17 at 08:21

mtoto

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Since ifelse is slow, maybe better to do `data[, reps := 13][year(Time)==2016, reps := 11-month(Time)][rep(1:.N, reps)]` – Frank Apr 20 '17 at 11:41
why `ifelse` is slow? – Peter Chen Apr 20 '17 at 11:53
2

@PeterChen http://stackoverflow.com/questions/16275149/does-ifelse-really-calculate-both-of-its-vectors-every-time-is-it-slow – Frank Apr 20 '17 at 12:28

R use ifelse to replicate

1 Answers1