Index list within map function - r

Question

This is a continuation from the previous question:
Apply function over every entry one table to every entry of another
I have the following tables loss.tib and bandstib and function bandedlossfn:
library(tidyverse)
set.seed(1)
n <- 5
loss.tib <- tibble(lossid = seq(n),
loss = rbeta(n, 1, 10) * 100)
bandstib <- tibble(bandid = seq(4),
start = seq(0, 75, by = 25),
end = seq(25, 100, by = 25))
bandedlossfn <- function(loss, start, end) {
pmin(end - start, pmax(0, loss - start))
}
It is possible to apply this function over loss.tib using bandstib as arguments:
loss.tib %>%
mutate(
result = map(
loss, ~ tibble(result = bandedlossfn(.x, bandstib$start,
bandstib$end))
)
) %>% unnest
However, I would like to add an index within map as follows:
loss.tib %>%
mutate(
result = map(
loss, ~ tibble(result = bandedlossfn(.x, bandstib$start,
bandstib$end)) %>%
mutate(bandid2 = row_number())
)
) %>% unnest
But it does not seem to work as intended.
I also want to add filter(!near(result,0)) within the map function too for efficient memory management.
The result I'm expecting is:
lossid loss bandid result
1 21.6691088 1 21.6691088
2 6.9390647 1 6.9390647
3 0.5822383 1 0.5822383
4 5.5671643 1 5.5671643
5 27.8237244 1 25.0000000
5 27.8237244 2 2.8237244
Thank you.

Answer 1

Here is one possibility:
you first nest bandstib and add it to loss.tib. This way the id sticks to your calculations:
bandstib <- tibble(bandid = seq(4),
start = seq(0, 75, by = 25),
end = seq(25, 100, by = 25)) %>%
nest(.key = "data")
set.seed(1)
n <- 5
result <- tibble(loss = rbeta(n, 1, 10) * 100) %>%
bind_cols(., slice(bandstib, rep(1, n))) %>%
mutate(result = map2(loss, data, ~bandedlossfn(.x, .y$start, .y$end))) %>%
unnest()