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The listcompr package is a light-weight collection of functions for list comprehension. It is intended as “syntactic sugar” for R and it is inspired by the list comprehension capabilities from ‘python’. Next to lists, similar structures like vectors (of numeric or character type), data frames, matrices, or named lists can be easily composed. The package may be used for the simple generation of small data sets for “textbook examples”, for unit tests of your R code, or for tiny mathematical tasks.
listcompr is on CRAN. To install the latest version from CRAN, simply use:
install.packages("listcompr")To install and load the latest development version from this repository, execute the following in R:
install.packages("devtools")
library(devtools)
install_github("patrickroocks/listcompr", build_vignettes = TRUE)
library(listcompr)We show the basic functionality to compose lists, vectors and data
frames. The first argument for each generator function
(gen.list, gen.vector,
gen.data.frame, and gen.matrix) is a base
expression, and the other arguments are variable ranges and
conditions.
First, we want to get a vector of all numbers in 1:10
which can be divided by 3 or 4:
gen.vector(i, i = 1:10, i %% 3 == 0 || i %% 4 == 0)
## Returns: c(3, 4, 6, 8, 9)Next we want to compose a list of tuples c(i, j) where
i and j are from 1:3
andi <= j holds:
gen.list(c(i, j), i = 1:3, j = i:3)
## Returns: list(c(1, 1), c(1, 2), c(2, 2), c(1, 3), c(2, 3), c(3, 3))There is also a function to compose a data frame which expects a
named vector as base expression. For example we can easily sum up
1:i while iterating over i:
gen.data.frame(c(a, sum = sum(1:a)), a = 1:10)The first three lines of this data frame are:
a sum
1 1 1
2 2 3
3 3 6In listcompr, the list and vector compositions can be nested. We create a vector containing all “perfect numbers” between 2 and 100, i.e., numbers where the sum of the divisors equals the number:
gen.vector(a, a = 2:100, a == sum(gen.vector(x, x = 1:(a-1), a %% x == 0)))
## Returns: c(6, 28)There are also functions to compose characters. For instance the
package offers a function gen.named.list, where the first
argument is the name (expressions in {}-brackets are
substituted) of each list entry. The remaining arguments are the same as
for gen.list. The following statement gives us all the
divisors between 5 and 10:
gen.named.list('divisors_of_{a}', gen.vector(x, x = 1:(a-1), a %% x == 0), a = 5:10)The last list entry has the name 'divisors_of_10' and
the content c(1, 2, 5).
After installation of the package, run
vignette("introduction", package = "listcompr")to see a vignette with some more examples.
To submit bugs or suggest improvements, feel free to open a issue or write a mail to me: Patrick Roocks, mail@p-roocks.de
These binaries (installable software) and packages are in development.
They may not be fully stable and should be used with caution. We make no claims about them.