fabR (version 2.1.0)

parceval: Shortcut to turn String character into R code

Description

Shortcut to parse() and eval() evaluate R expression in a character string, and turns it into actual R code. This function is targeted for interaction with external files (where expression is stored in text format) ; for tidy elements where code expression is generated using dplyr::mutate(), combined with paste0() ; in for while, map, etc. loops where character string expression can be indexed or iteratively generated and evaluated ; objects to be created (using assign, <- or <<- obj) where the name of the R object is stored in a string. Some issues may occur when parceval is used in a different environment, such as in a function. Prefer eval(parse(text = ...) instead.

Usage

parceval(...)

Value

Any output generated by the evaluation of the string character.

Arguments

...

String character to be parsed and evaluated

See Also

parse(), eval()

Examples

{

##### Example 1 -------------------------------------------------------------
# Simple assignation will assign 'b' in parceval environment (which is
# associated to a function and different from .GlobalEnv, by definition).
# Double assignation will put 'b' in .GlobalEnv.
# (similar to assign(x = "b",value = 1,envir = .GlobalEnv))

a <- 1
parceval("print(a)")

##### Example 2 -------------------------------------------------------------
# use rowwise to directly use parceval in a tibble, or use a for loop.
library(dplyr)
library(tidyr)

tibble(cars) %>%
  mutate(
    to_eval = paste0(speed,"/",dist)) %>%
  rowwise() %>%
  mutate(
    eval = parceval(to_eval))

##### Example 3 -------------------------------------------------------------
# parceval can be parcevaled itself!

code_R <-
  'as_tibble(cars) %>%
  mutate(
    to_eval = paste0(speed,"/",dist)) %>%
  rowwise() %>%
  mutate(
    eval = parceval(to_eval))'

cat(code_R)
parceval(code_R)

}