Expand SQL tables to include all possible combinations of values

Source: R/verb-expand.R

This is a method for the tidyr::expand generics. It doesn't sort the result explicitly, so the order might be different to what expand() returns for data frames.

# S3 method for class 'tbl_lazy'
expand(data, ..., .name_repair = "check_unique")

Arguments

data

A lazy data frame backed by a database query.

...

Specification of columns to expand. See tidyr::expand for more details.

.name_repair

Treatment of problematic column names:

  • "minimal": No name repair or checks, beyond basic existence,

  • "unique": Make sure names are unique and not empty,

  • "check_unique": (default value), no name repair, but check they are unique,

  • "universal": Make the names unique and syntactic

  • "unique_quiet": Same as "unique", but "quiet"

  • "universal_quiet": Same as "universal", but "quiet"

  • a function: apply custom name repair (e.g., .name_repair = make.names for names in the style of base R).

  • A purrr-style anonymous function, see rlang::as_function()

This argument is passed on as repair to vctrs::vec_as_names(). See there for more details on these terms and the strategies used to enforce them.

Value

Another tbl_lazy. Use dplyr::show_query() to see the generated query, and use collect() to execute the query and return data to R.

Examples

fruits <- memdb_frame(
  type   = c("apple", "orange", "apple", "orange", "orange", "orange"),
  year   = c(2010, 2010, 2012, 2010, 2010, 2012),
  size = c("XS", "S",  "M", "S", "S", "M"),
  weights = rnorm(6)
)

# All possible combinations ---------------------------------------
fruits %>% tidyr::expand(type)
#> # Source:   SQL [?? x 1]
#> # Database: sqlite 3.50.4 [:memory:]
#>   type  
#>   <chr> 
#> 1 apple 
#> 2 orange
fruits %>% tidyr::expand(type, size)
#> # Source:   SQL [?? x 2]
#> # Database: sqlite 3.50.4 [:memory:]
#>   type   size 
#>   <chr>  <chr>
#> 1 apple  XS   
#> 2 apple  S    
#> 3 apple  M    
#> 4 orange XS   
#> 5 orange S    
#> 6 orange M    

# Only combinations that already appear in the data ---------------
fruits %>% tidyr::expand(nesting(type, size))
#> # Source:   SQL [?? x 2]
#> # Database: sqlite 3.50.4 [:memory:]
#>   type   size 
#>   <chr>  <chr>
#> 1 apple  XS   
#> 2 orange S    
#> 3 apple  M    
#> 4 orange M