Plot multiple lines (data series) each with unique color in R

I am fairly new to R and I have the following queries :

I am trying to generate a plot in R which has multiple lines (data series). Each of these lines is a category and I want it to have a unique color.

Currently my code is setup in this way :

First, I am creating an empty plot :

plot(1,type='n',xlim=c(1,10),ylim=c(0,max_y),xlab='ID', ylab='Frequency')

Then for each of my category, I am plotting lines in this empty plot using a “for” loop like so :

for (category in categories){
lines(data.frame.for.this.category, type='o', col=sample(rainbow(10)), lwd=2)
}

There are 8 categories here, and so there are 8 lines produced in the plot. As you can see, I am trying to sample a color from the rainbows() function to generate a color for each line.

However, when the plot is generated, I find that there are multiple lines which have the same color. For instance, 3 of those 8 lines have green color.

How do I make each of these 8 lines have a unique color ?

Also, how do I reflect this uniqueness in the legend of the plot ? I was trying to lookup the legend() function, however it was not clear which parameter I should use to reflect this unique color for each category ?

Any help or suggestions would be much appreciated.