R: changing plot colors

Question

I made the following plot in R :

library(MASS)

a = rnorm(100, 10, 10)

b = rnorm(100, 10, 5)

c = rnorm(100, 5, 10)

group <- sample( LETTERS[1:4], 100, replace=TRUE, prob=c(0.25, 0.25, 0.25, 0.25) )

d = data.frame(a, b, c, group)
d$group = as.factor(d$group)

  parcoord(d[, c(3, 1, 2)], col = 1 + (0:149) %/% 50)
title(main = "Plot", xlab = "Variable", ylab = "Values")
axis(side = 2, at = seq(0, 5, 0.1),
     tick = TRUE, las = 1)

Can someone please show me how to color each line in this plot according the value of "d$group" and add a legend in the corner of the screen?

I think the following line of code changes the color of lines per value of "d$group":

parcoord(d[, c(3, 1, 2)], col = d$group)

And this line of code creates a legend:

legend( "topleft", c("A", "B", "C", "D"), 
text.col=c("blue", "red", "yellow", "green") )

title("Legend",
      cex.main = 1.1)

But I am not sure how to have the colors from the legend match the real colors. I tried:

legend( "topleft", c("A", "B", "C", "D"), 
text.col= d$group)

But this did not work. Can someone please show me how to fix this?

Thanks

EDIT: is there a way to run the code (provided in the answer) if variable "C" is a factor?

e.g.

a = rnorm(100, 10, 10)

b = rnorm(100, 10, 5)

c <- sample( LETTERS[1:2], 100, replace=TRUE, prob=c(0.5,0.5) )

group <- sample( LETTERS[1:4], 100, replace=TRUE, prob=c(0.25, 0.25, 0.25, 0.25) )

d = data.frame(a, b, c, group)
d$group = as.factor(d$group)
d$c = as.factor(d$c)


library(tidyverse)
library(ggplot2)
library(dplyr)

d %>% 
  mutate(rn = row_number()) %>% 
  pivot_longer(a:c) %>% 
  ggplot(aes(name, value, group = rn, color = group)) +
  scale_x_discrete(expand = expansion(0, 0)) +
  geom_line()

question from:https://stackoverflow.com/questions/65839197/r-changing-plot-colors

Answer 1

a = rnorm(100, 10, 10)

b = rnorm(100, 10, 5)

c <- sample( LETTERS[1:2], 100, replace=TRUE, prob=c(0.5,0.5) )

group <- sample( LETTERS[1:4], 100, replace=TRUE, prob=c(0.25, 0.25, 0.25, 0.25) )

d = data.frame(a, b, c, group)
d$group = as.factor(d$group)
d$c = as.factor(d$c)


library(tidyverse)
library(ggplot2)
library(dplyr)

d %>% 
  mutate(rn = row_number()) %>% 
  reshape2::melt(id=c("group","c","rn")) %>% 
  ggplot(aes(variable, value, group = rn, color = group)) +
  scale_x_discrete(expand = expansion(0, 0)) +
  geom_line()+
  facet_wrap(c~.,)

I have done some modifications in the code, and you can add c as a factor in the code.