README.md

struct

{struct} provides ways to modify objects more strictly, guaranteeing that we keep the type of the modified element, where type is defined by vctrs::vec_ptype().

The struct() function gives a subclass “struct” to the objects if its internal type is list (thus including data frames), and recursively to its list components.

When assigning new values, we give it the “struct” subclass if relevant then use vctrs::vec_cast() to check the compatibility of the input with the output, and apply coercion if necessary.

Installation

Install with:

remotes::install_github("cynkra/struct")

Example

library(struct)
library(tibble)

x1 <- list(
  a = 1,
  b = list(tibble(c = 3:4, d = 5:6)),
  c = tibble(e = 7:8, f = 9:10),
  y = list(z = c("a", "b"))
)
x2 <- deep_struct(x1)

x2
#> # list_struct object: 4 element(s)
#>   a            b                        c                  y             
#> * <dbl>        <list<tbbl_str[,2]>>     <tbbl_str[,2]>     <named list>  
#> 1 <scalar [1]> <list<tbbl_str[,2]> [1]> <tbbl_str [2 × 2]> <lst_strc [1]>

print_tree(x2)
#> █─ x2 <lst_strc>
#> ├─── a <scalar>
#> ├─█─ b <list<tbbl_str[,2]>>
#> ├─█─ c <tbbl_str[,2]>
#>   ├─── e <int>
#>   ├─── f <int>
#> ├─█─ y <lst_strc>
#>   ├─── z <chr>

# works
x2$a <- 11
x2$b <- list(tibble(c = 13:14, d = 15:16))
x2$c <- tibble(e = 17:18, f = 19:20)

# fails
x2$a <- c(11, 12)
#> Error in `struct_cast()` at struct/R/modify.R:8:3:
#> ! not a scalar
x2$a <- "a"
#> Error in `structure()` at struct/R/classes.R:52:11:
#> ! Can't convert `new` <character> to <double>.
x2$b <- list("a", "b")
#> Error in `struct_cast()` at struct/R/modify.R:8:3:
#> ! Can't convert `..1` <character> to <tibble_struct>.
x2$c <- 1
#> Error in `struct_cast()` at struct/R/modify.R:8:3:
#> ! Can't convert `new` <double> to <tbl_df>.
x2[["z"]]
#> Error in `x2[["z"]]`:
#> ! Invalid index
#> ✖ element `z` not found