different behavior b/w modify_depth and at_depth

[lmwang9527]

With at_depth in purrr pre-0.2.3, it is possible to run the following code, but modify_depth breaks the code as it tries to modify .x. I understand modify_depth may not be intended to be backward-compatible, but is there an alternative function with at_depth like behavior in 0.2.3?

Thanks for the powerful package and the improvement in the new version!

# See https://stackoverflow.com/a/43861746/688693 for more details
devtools::install_version("purrr", version = "0.2.2.2", repos = "http://cran.us.r-project.org")

library(gapminder)
library(dplyr)
library(tidyr)
library(purrr)
library(broom)

fmlas <- tibble::tribble(
  ~continent, ~formula,
  "Asia", ~lm(lifeExp ~ year, data = .),
  "Europe", ~lm(lifeExp ~ year + pop, data = .),
  "Africa", ~lm(lifeExp ~ year + gdpPercap, data = .),
  "Americas", ~lm(lifeExp ~ year - 1, data = .),
  "Oceania", ~lm(lifeExp ~ year + pop + gdpPercap, data = .)
)

by_continent <- gapminder %>% 
  nest(-continent) %>%
  left_join(fmlas) %>%
  mutate(model=map2(data, formula, ~at_depth(.x, 0, .y)))

by_continent %>% 
  mutate(glance=map(model, glance)) %>% 
  unnest(glance, .drop=T)

detach(package:purrr, unload=TRUE)
devtools::install_version("purrr", version = "0.2.3", repos = "http://cran.us.r-project.org")
library(purrr)

by_continent <- gapminder %>% 
  nest(-continent) %>%
  left_join(fmlas) %>%
  mutate(model=map2(data, formula, ~modify_depth(.x, 0, .y)))
# Error in mutate_impl(.data, dots) : 
#   Evaluation error: replacement element 7 has 5 rows, need 396.

## OR
by_continent <- gapminder %>% 
  nest(-continent) %>%
  left_join(fmlas) %>%
  mutate(model=map2(data, formula, ~modify(.x, .y)))
#Error in mutate_impl(.data, dots) : 
#  Evaluation error: object 'lifeExp' not found.

[hadley]

Duplicate of #381