Applying a function to a nested list - r

Question

I have a data frame that contains nested list based on ID. I am trying to apply a function to the nested list within this data frame, but I am running into this error:
Error in make_track(tbl = x, .x = x, .y = y, .t = date, uid = ID, crs = sp::CRS("+init=epsg:32612")) : Non existent columns from tbl were requested.
Here is my reproducible example. I was wondering what the best way to apply a function to a nested list might be, and how I can go about fixing this error. Do I have to do a double lapply to fix this problem?
set.seed(12345)
library(lubridate)
library(dplyr)
library(amt)
f = function(data){
data %>% mutate(
new = floor_date(data$date, "10 days"),
new = if_else(day(new) == 31, new - days(10), new)
) %>%
group_split(new)
}
nested <- tibble(
ID = rep(c("A","B","C","D", "E"), 100),
date = rep_len(seq(dmy("01-01-2010"), dmy("31-12-2013"), by = "days"), 500),
x = runif(length(date), min = 60000, max = 80000),
y = runif(length(date), min = 800000, max = 900000)
) %>% group_by(ID) %>%
nest() %>%
mutate(data = map(data, f))
track_list <- lapply(nested, function (x){
make_track(tbl = x, .x = x, .y = y, .t = date,
uid = ID,
# lat/long: 4326 (lat/long, WGS84 datum).
# utm: crs = sp::CRS("+init=epsg:32612"))
crs = sp::CRS("+init=epsg:32612"))
})

Answer 1

The issue is that the data is nested, so we need to do one more level inside to pick up the data. Also, the make_track requires all columns to be in the same data object, so we need to create the corresponding uid from the 'ID' column of nested object
library(purrr)
library(dplyr)
library(amt)
out <- map2_dfr(nested$ID, nested$data, function(z, lst1)
map_dfr(lst1, ~ {
dat <- .x %>%
mutate(ID = z)
make_track(tbl = dat, .x = x, .y = y, .t = date, uid = ID,
crs = sp::CRS("+init=epsg:32612"))
}))
-output
> out
# A tibble: 500 x 4
x_ y_ t_ uid
<dbl> <dbl> <date> <chr>
1 74418. 820935. 2010-01-01 A
2 63327. 885896. 2010-01-06 A
3 60691. 873949. 2010-01-11 A
4 69250. 868411. 2010-01-16 A
5 69075. 876142. 2010-01-21 A
6 67797. 829892. 2010-01-26 A
7 75860. 843542. 2010-01-31 A
8 67233. 882318. 2010-02-05 A
9 75644. 826283. 2010-02-10 A
10 66424. 853789. 2010-02-15 A
# … with 490 more rows
If we want the output as a nested list, use remove the _dfr
out <- map2(nested$ID, nested$data, function(z, lst1)
map(lst1, ~ {
dat <- .x %>%
mutate(ID = z)
make_track(tbl = dat, .x = x, .y = y, .t = date, uid = ID,
crs = sp::CRS("+init=epsg:32612"))
}))