The problem

I’m currently (finally) learning more about linear algebra, statistical optimisation, and other matrix-related topics. While learning about such abstract topics, for me it really helps to convert the material into small R programs. While doing this, I stumbled upon a problem: Matrix construction in R kind of sucks. Why? Look at this:

M <- matrix(c(1, 0.2, -0.3, 0.4,
              0.2, 1, 0.6, -0.4,
              -0.3, 0.6, 1, 0.4,
              0.4, -0.4, 0.4, 1),
            nrow = 4,
            ncol = 4,
            byrow = TRUE)

If I want to create a matrix, I need to (a) create a full vector of values to put in the matrix, (b) decide into how many rows/columns I want to put these values, and (c) decide whether to fill these values in a columnwise (default) or rowwise manner. This last step in particular is a nuisance, because the default makes sure we cannot have any form of “what you see is what you get” (WYSIWYG) in our script.

The solution

To solve this issue for people who want to rapidly create legible matrices, I created the package Massign. This package has only one operator, %<-%, and it works as follows to create the same matrix as above:

M %<-% "   1
         0.2,    1
        -0.3,  0.6,    1
         0.4, -0.4,  0.4,    1"

Neat right? There are a few features to it:

WYSIWYG Matrix Construction

In it’s most basic form, Massign makes for legible code because of the “what you see is what you get” nature of the matrix construction function.

M %<-% "   1,  0.2, -0.3,  0.4
         0.2,    1,  0.6, -0.4
        -0.3,  0.6,    1,  0.4
         0.4, -0.4,  0.4,    1"
M

##      [,1] [,2] [,3] [,4]
## [1,]  1.0  0.2 -0.3  0.4
## [2,]  0.2  1.0  0.6 -0.4
## [3,] -0.3  0.6  1.0  0.4
## [4,]  0.4 -0.4  0.4  1.0

Automatic Symmetric Construction

As shown before, when you enter a lower triangular matrix, Massign automatically creates a symmetric matrix. This is a major feature, because properly creating the symmetric elements is not simple using the default matrix() function.

Variables Allowed

Because Massign constructs a matrix() call under the hood and evaluates it in the environment in which the function is called, it is allowed to enter variables inside the text string:

phi <- 1.5
M %<-% "1,     1,     1
        1,   phi, phi^2
        1, phi^2, phi^4"
M

##      [,1] [,2]   [,3]
## [1,]    1 1.00 1.0000
## [2,]    1 1.50 2.2500
## [3,]    1 2.25 5.0625

For the same reason, complex numbers work too. It does only work with numbers, though, so for character matrices you’re stuck with the matrix() function for now.

Conclusion

The %<-% operator in Massign makes life a little easier for R programmers who want to quickly construct a relatively small matrix for prototyping or learning. Take this code piece for generating an 8-dimensional multivariate normal distribution with positive correlations:

library(Massign)
library(MASS)

## 
## Attaching package: 'MASS'

## The following object is masked from 'package:dplyr':
## 
##     select

S %<-% "  1,
         .5,   1
         .5,  .5,   1
         .5,  .5,  .5,   1
         .5,  .5,  .5,  .5,   1
         .6,  .6,  .6,  .6,  .6,   1
         .5,  .5,  .5,  .5,  .5,  .5,   1
         .4,  .4,  .4,  .4,  .4,  .4,  .4,  1"

X <- mvrnorm(10, mu = rep(0,8), Sigma = S)

The package is on CRAN, so you can install it as follows:

install.packages("Massign")

If you have any complaints, tips, issues, or suggestions, you can submit an issue on the project’s GitHub page. Here you can also view the source code of the package!