ptr {pointr}

Working with pointers

Description

Create, remove and analyze pointers in R. Pointers can point to any R object, including selections/subsets.

Usage

ptr(symbol1, symbol2)

symbol1 %=% symbol2

rm.ptr(symbol1, keep = FALSE)

where.ptr(symbol1)

Arguments

symbol1

The name of the pointer, as a one-element character vector.

symbol2

The object/selection the pointer will point to, as a one-element character vector.

keep

A logical value relevant when removing a pointer with rm.ptr. If TRUE, the pointer variable will be kept and filled with a copy of the object the pointers points to; if FALSE, the pointer variable symbol1 will be removed completely. Default is FALSE.

Details

The ptr() function and the %=% operator will create a pointer to an R object, like a vector, list, dataframe or even a subset/selection from a dataframe. where.ptr() shows where a pointer actually points to. Existing pointers can be removed usig the rm.ptr() function. Pointers created with pointr use active bindings that call a hidden access function everytime the pointer is accessed. This hidden access function is named .pointer() (where pointer is the name of the pointer variable) and is created in the environment from which ptr() is called. It is not necessary to call this hidden access function as a pointer user. The hidden access function is removed when rm.ptr() is called.

Value

ptr(), %=% and rm.ptr() have no return value. ptr() and %=% create the pointer variable (argument symbol1) in the environment from which it is called. where.ptr returns the object/selection a pointer points to as a character vector.

Contributions

Thanks to Chad Hammerquist for contributing the pointr operator %=%.

Examples

library(pointr)

# Pointer to simple variable

myvar <- 3
ptr("mypointer", "myvar")
mypointer

myvar <- 5
mypointer

mypointer <- 7
myvar


# Alternative: Use the pointr operator %=%

myvar <- 3
mypointr %=% myvar
myvar


# Pointer to subset from dataframe

df <- data.frame(list(var1 = c(1,2,3), var2 = c("a", "b", "c")), stringsAsFactors = FALSE)
df

i <- 2
ptr("sel", "df$var2[i]")

sel <- "hello"
df$var2[i]

df$var2[i] <- "world"
sel

where.ptr("sel")