Can't use [[ with scoped mutate

[copernican]

I want to dynamically extract one or more keys from a map column using the new remote evaluation of [[. I would expect each of the cases in the reprex below to give equivalent output.

ID	map column name	map column quoted	verb	works as expected
1	x	no	mutate()	yes
2	x	no	mutate_at()	no
3	x	yes	mutate()	no
4	x	yes	mutate_at()	no
5	x	no	extract_keys()	no
6	dim	no	extract_keys()	yes

My best guess is that there is some interaction among [[, mutate_at(), and quasiquotation. The target DB is Presto, but this issue doesn't appear specific to Presto. Also, I suspect this is related to other recent issues, e.g., #305.

library(dplyr, warn.conflicts = FALSE)
library(dbplyr, warn.conflicts = FALSE)
library(purrr)
library(rlang, warn.conflicts = FALSE)

build_extractor <- function(map, key) {
  key_chr <- rlang::as_name(dplyr::enquo(key))
  map_quo <- rlang::enquo(map)
  rlang::list2(!!key_chr := ~ `[[`(!!map_quo, !!key_chr))
}

extract_keys <- function(.data, map, ...) {
  map_quo <- rlang::enquo(map)
  keys <- rlang::enquos(...)

  extractors <-
    keys %>%
    purrr::map(build_extractor, map = !!map_quo) %>%
    purrr::reduce(c)

  .data %>%
    dplyr::mutate_at(dplyr::vars(!!map_quo), extractors)
}

df <- tibble(x = list(c(a = 1, b = 2), c(a = 3, b = 4)))
df_dbi <- tbl_lazy(df)
map_var <- dplyr::quo(x)

df_dbi %>% mutate(a = x[["a"]], b = x[["b"]])
#> <SQL>
#> SELECT `x`, `x`.`a` AS `a`, `x`.`b` AS `b`
#> FROM `df`

df_dbi %>% mutate_at(vars(x), list(a = ~`[[`(., "a"), b = ~`[[`(., "b")))
#> Error in as.pairlist(list(...)): object 'x' not found

df_dbi %>% mutate(a = !!map_var[["a"]], b = !!map_var[["b"]])
#> <SQL>
#> SELECT `x`
#> FROM `df`

df_dbi %>% mutate_at(vars(!!map_var), list(a = ~`[[`(., "a"), b = ~`[[`(., "b")))
#> Error in as.pairlist(list(...)): object 'x' not found

df_dbi %>% extract_keys(x, a, b)
#> Error in as.pairlist(list(...)): object 'x' not found

df_dbi %>% rename(dim = x) %>% extract_keys(dim, a, b)
#> <SQL>
#> SELECT `dim`, `dim`.`a` AS `a`, `dim`.`b` AS `b`
#> FROM (SELECT `x` AS `dim`
#> FROM `df`) `dbplyr_001`

^{Created on 2019-05-20 by the reprex package (v0.3.0)}

Session info

devtools::session_info()
#> ─ Session info ──────────────────────────────────────────────────────────
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#>  date     2019-05-20                  
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#> [2] /usr/lib/R/library

[hadley]

There's a lot going on in your reprex, but it seems like all of the problems have the same error, so I think it makes sense to fix that first:

library(dbplyr)
library(dplyr, warn.conflicts = FALSE)

lf <- lazy_frame(x = list(c(a = 1, b = 2), c(a = 3, b = 4)))
lf %>% mutate_at(vars(x), list(a = ~`[[`(., "a"), b = ~`[[`(., "b")))
#> <SQL>
#> Error in x[[]]: argument "i" is missing, with no default

^{Created on 2019-05-30 by the reprex package (v0.2.1.9000)}

I see a different error message to you, but the most likely explanation is that I have some development version of something installed at the moment.

[hadley]

Simpler reprex with slightly different error:

library(dbplyr)
library(dplyr, warn.conflicts = FALSE)

lf <- lazy_frame(x = list(c(a = 1, b = 2), c(a = 3, b = 4)))
lf %>% mutate_all(list(a = ~ .$a, b = ~ .$b))
#> <SQL>
#> Error in eval_bare(x, .env): argument "y" is missing, with no default

^{Created on 2019-05-30 by the reprex package (v0.2.1.9000)}

[hadley]

Installed cran dplyr and now I'm getting the same error as above.

[copernican]

As a follow-up, I've discovered that using the names of other functions for the list column "avoids" the error, though the output does not appear correct, either. It just so happened that I noticed the dim case above because that was the name of a column in a database table I was using.

library(dbplyr)
library(dplyr, warn.conflicts = FALSE)

lf0 <- lazy_frame(x = list(c(a = 1, b = 2), c(a = 3, b = 4)))
lf0 %>% mutate_all(list(a = ~ .$a, b = ~ .$b))
#> Error in as.pairlist(list(...)): object 'x' not found

lf1 <- lazy_frame(match = list(c(a = 1, b = 2), c(a = 3, b = 4)))
lf1 %>% mutate_all(list(a = ~ .$a, b = ~ .$b))
#> <SQL>
#> SELECT `match`, `.`.`a` AS `a`, `.`.`b` AS `b`
#> FROM `df`

lf2 <- lazy_frame(filter = list(c(a = 1, b = 2), c(a = 3, b = 4)))  
lf2 %>% mutate_all(list(a = ~ .$a, b = ~ .$b))
#> <SQL>
#> SELECT `filter`, `.`.`a` AS `a`, `.`.`b` AS `b`
#> FROM `df`

^{Created on 2019-06-04 by the reprex package (v0.3.0)}