Yet another operator to simplify data preparation with memisc

20 August 2023

The recently published version 0.99.31.6 of the memisc package also contains an %$$% operator that simplifies routine data preparation steps that hitherto would involve calls to the function within(). It is analogous to the operator %$%, which is provided by the “magrittr” package, but is also defined by this package.

These operators are illustrated by the following code examples.

library(magrittr)
library(memisc) 
set.seed(42)

Here we create a simple example data frame:

df <- data.frame(a = 1:7, x = rnorm(7))
df

The following code creates two new variables b and x.sq in the data frame using within():

df <- within(df,{
    b <- a + 4
    x.sq <- x^2
})
df

This is a bit tedious, because we have to write the name of the data frame (i.e. “df”) twice. Using the operator %<>% from the magrittr package one needs to write the name of the data frame only once:

df %<>% within({
    b <- a + 4
    x.sq <- x^2
})
df

The magrittr package defines an operator %$% that can be used as a shorthand for with():

with(df, mean(x))

df %$% mean(x)

Thus it does not seem to be far-fetched to use an analogous shorthand for within() - which is defined in the most recent version of memisc:

df[c("b","x.sq")] <- NULL

df %$$% {
    b <- a + 4
    x.sq <- x^2
}
df

Beside being shorter than a call to within(), it results in a data frame (or data set) in which the variables are ordered by their creation - variables created frist, appear first in the resulting data frame.