plot - R: non-numeric arguments to binary operators

Question

I am working with the R programming language. I am trying to make a "parallel coordinates plot" using some fake data:

library(MASS)

a = rnorm(100, 10, 10)

b = rnorm(100, 10, 5)

c = rnorm(100, 5, 10)

d = matrix(a, b, c)

parcoord(d[, c(3, 1, 2)], col = 1 + (0:149) %/% 50)

However, a problem arises when I try to mix numeric and factor variables together:

group <- sample( LETTERS[1:4], 100, replace=TRUE, prob=c(0.25, 0.25, 0.25, 0.25) )
d = matrix(a,b, group)
 parcoord(d[, c(3, 1, 2)], col = 1 + (0:149) %/% 50)

Error in x - min(x, na.rm = TRUE): non-numeric argument to binary operator

I am just curious. Can this problem be resolved? Or is it simply impossible to make such a plot using numeric and factor variables together?

I saw a previous stackoverflow post over here where a similar plot is made using numeric and factor variables: How to plot parallel coordinates with multiple categorical variables in R

However, I am using a computer with no USB port or internet access - I have a pre-installed version of R with limited libraries (I have plotly, ggplot2, dplyr, MASS ... I don't have ggally or tidyverse) and was looking for a way to do this only with the parcoord() function.

Does anyone have any ideas if this can be done? Thanks

Thanks

Answer 1

One option is to label rows of the matrix using a factor and use that on the plot, e.g.

library(MASS)
set.seed(300)
par(xpd=TRUE)
par(mar=c(4, 4, 4, 6))
a = rnorm(12, 10, 10)
b = rnorm(12, 10, 5)
c = rnorm(12, 5, 10)
group <- sample(c("#FF9289", "#FF8AFF", "#00DB98", "#00CBFF"),
                12, replace=TRUE)

d = cbind(a, b, c)
rownames(d) <- group

parcoord(d[, c(3, 1, 2)], col = group)
title(main = "Plot", xlab = "Variable", ylab = "Values")
axis(side = 2, at = seq(0, 1, 0.1),
     tick = TRUE, las = 1)
legend(3.05, 1, legend = c("A", "B", "C", "D"), lty = 1,
       col = c("#FF9289", "#FF8AFF", "#00DB98", "#00CBFF"))

EDIT

Thanks for the additional explanation. What you want does make sense, but unfortunately it doesn't look like it will work as I expected. I tried to make a plot using an ordered factor as the middle variable (per https://pasteboard.co/JKK4AUD.jpg) but got the same error ("non-numeric argument to binary operator").

One way I thought of doing it is to recode the factor as a number (e.g. "Var_1" -> 0.2, "Var_2" -> 0.4) as below:

library(MASS)
set.seed(123)
par(xpd=TRUE)
par(mar=c(4, 4, 4, 6))
a = rnorm(12, 10, 10)
b = c(rep("Var_1", 3),
      rep("Var_2", 3),
      rep("Var_3", 3),
      rep("Var_4", 3))
c = rnorm(12, 5, 10)
group <- c(rep("#FF9289", 3),
           rep("#FF8AFF", 3),
           rep("#00DB98", 3),
           rep("#00CBFF", 3))

d = data.frame("A" = a,
               "Factor" = b,
               "C" = c,
               "Group" = group)

d$Factor <- sapply(d$Factor, switch,
                   "Var_1" = 0.8,
                   "Var_2" = 0.6,
                   "Var_3" = 0.4,
                   "Var_4" = 0.2)

parcoord(d[, c(1, 2, 3)], col = group)
title(main = "Plot", xlab = "Variable", ylab = "Values")
axis(side = 2, at = seq(0, 1, 0.1),
     tick = TRUE, las = 1)
legend(3.05, 1, legend = c("A", "B", "C", "D"), lty = 1,
       col = c("#FF9289", "#FF8AFF", "#00DB98", "#00CBFF"))
mtext(text = "Var 1", side = 1, adj = 0.6, padj = -30)
mtext(text = "Var 3", side = 1, adj = 0.6, padj = -12)
mtext(text = "Var 2", side = 1, adj = 0.6, padj = -21)
mtext(text = "Var 4", side = 1, adj = 0.6, padj = -3)