R - dplyr map slice for repeat rows - r

Question

I have trouble combining slice and map.
I am interested of doing something similar to this; which is, in my case, transforming a compact person-period file to a long (sequential) person-period one. However, because my file is too big, I need to split the data first.
My data look like this
group id var ep dur
1 A 1 a 1 20
2 A 1 b 2 10
3 A 1 a 3 5
4 A 2 b 1 5
5 A 2 b 2 10
6 A 2 b 3 15
7 B 1 a 1 20
8 B 1 a 2 10
9 B 1 a 3 10
10 B 2 c 1 20
11 B 2 c 2 5
12 B 2 c 3 10
What I need is simply this (answer from this)
library(dplyr)
dt %>% slice(rep(1:n(),.$dur))
However, I am interested in introducing a split(.$group).
How I am suppose to do so ?
dt %>% split(.$group) %>% map_df(slice(rep(1:n(),.$dur)))
Is not working for example.
My desired output is the same as dt %>% slice(rep(1:n(),.$dur))
which is
group id var ep dur
1 A 1 a 1 20
2 A 1 a 1 20
3 A 1 a 1 20
4 A 1 a 1 20
5 A 1 a 1 20
6 A 1 a 1 20
7 A 1 a 1 20
8 A 1 a 1 20
9 A 1 a 1 20
10 A 1 a 1 20
.....
But I need to split this operation because the file is too big.
data
dt = structure(list(group = structure(c(1L, 1L, 1L, 1L, 1L, 1L, 2L,
2L, 2L, 2L, 2L, 2L), .Label = c("A", "B"), class = "factor"),
id = structure(c(1L, 1L, 1L, 2L, 2L, 2L, 1L, 1L, 1L, 2L,
2L, 2L), .Label = c("1", "2"), class = "factor"), var = structure(c(1L,
2L, 1L, 2L, 2L, 2L, 1L, 1L, 1L, 3L, 3L, 3L), .Label = c("a",
"b", "c"), class = "factor"), ep = structure(c(1L, 2L, 3L,
1L, 2L, 3L, 1L, 2L, 3L, 1L, 2L, 3L), .Label = c("1", "2",
"3"), class = "factor"), dur = c(20, 10, 5, 5, 10, 15, 20,
10, 10, 20, 5, 10)), .Names = c("group", "id", "var", "ep",
"dur"), row.names = c(NA, -12L), class = "data.frame")

Answer 1

map takes two arguments: a vector/list in .x and a function in .f. It then applies .f on all elements in .x.
The function you are passing to map is not formatted correctly. Try this:
f <- function(x) x %>% slice(rep(1:n(), .$dur))
dt %>%
split(.$group) %>%
map_df(f)
You could also use it like this:
dt %>%
split(.$group) %>%
map_df(slice, rep(1:n(), dur))
This time you directly pass the slice function to map with additional parameters.

Answer 2

I'm not quite sure what your desired final output is, but you could use tidyr to nest the data that you want to repeat and a simple function to expand levels of your nested data, very similar to Tutuchan's answer.
expand_df <- function(df, repeats) {
df %>% slice(rep(1:n(), repeats))
}
dt %>%
tidyr::nest(var:ep) %>%
mutate(expanded = purrr::map2(data, dur, expand_df)) %>%
select(-data) %>%
tidyr::unnest()
Tutuchan's answer gives exactly the same output as your original approach - is that what you were looking for? I don't know if it will have any advantage over your original method.