如何用dplyr引用变量而不是列

Question

When using dplyr:filter, I often compute a local variable that holds the viable choices:

df <- as_tibble(data.frame(id=c("a","b"), val=1:6))
ids <- c("b","c")
filter(df, id %in% ids)
# giving id %in% c("b","c")

However, if the dataset by chance has a column with the same name, this fails to achieve the intended purpose:

df$ids <- "a"
filter(df, id %in% ids)
# giving id %in% "a"

How should I explicitly refer to the ids variable instead of the ids column?

Answer 1

Unquote with !! to tell filter to look in the calling environment instead of the data frame:

library(tidyverse)

df <- data_frame(id = rep(c("a","b"), 3), val = 1:6)
ids <- c("b", "c")

df %>% filter(id %in% ids)
#> # A tibble: 3 x 2
#>      id   val
#>   <chr> <int>
#> 1     b     2
#> 2     b     4
#> 3     b     6

df <- df %>% mutate(ids = "a")

df %>% filter(id %in% ids)
#> # A tibble: 3 x 3
#>      id   val   ids
#>   <chr> <int> <chr>
#> 1     a     1     a
#> 2     a     3     a
#> 3     a     5     a

df %>% filter(id %in% !!ids)
#> # A tibble: 3 x 3
#>      id   val   ids
#>   <chr> <int> <chr>
#> 1     b     2     a
#> 2     b     4     a
#> 3     b     6     a

Of course, the better way to avoid such issues is to not put identically-named vectors in your global environment.