A helper for creating modules. Checks for previous module outputs in a chain and returns the named list item if it exists in any parent environment.
Usage
get_prev_outputs(module, item, parent_n = 2)
Arguments
- module
the name of a previously run module
- item
the name of the list item to extract
- parent_n
the number of parents to traverse up the chain. Noramlly 2 if you are calling this from a module function, but maybe more if you are calling it from a helper function.
Value
the extracted list item, or NULL if not found
Examples
# .__mc__prev_outputs is usually created by `module_run()`
.__mc__prev_outputs <- list(mod_1 = list(a = 1, b = 2))
f <- function(item) { get_prev_outputs("mod_1", item) }
f("a")
#> [1] 1
f("d")
#> NULL
