如何在R中的单个图上用不同的颜色绘制多条线？

Question

I have a data set that consists of cumulative counts of three species of fish for successive transects so this consists of 3 columns (species, count, transect);

eg

Species Count Transect
Cod     25    1
Cod     36    2
Cod     45    3
Haddock 12    1
Haddock 23    2
Haddock 34    3

Etc… I'm likely to have lots of species that I want to plot in a single plot so I have tried to use a loop (my first go at properly trying to use loops!!) to speed this up and have done the following

xrange <- range(Data$Transect)
ymax <- max(Data$Count)
plot(xrange,y=c(0,ymax+10),  yaxs = "i", type="n", las=1, xlab="Transect      Number", ylab="Total Number")
for (i in Data$Species){
species <- subset(Data, Species==i) 
lines(species$Transect, species$Count, type="o",lwd=2,lty=1,pch=NA)}

This produces a plot with all the species in the data set with a separate line but I would like each of these lines to have a unique colour and am struggling to do this.

I have tried the following but it doesn't work and all of the lines still come out as the same colour and I'm not sure what to try next?

nspecies <- levels(Data$Species)
colors<- rainbow(nspecies)
for (i in Data$Species) { 
species <- subset(Trial, Species==i) 
lines(species$Haul, species$Catch, type="o",lwd=2,lty=1,pch=NA,   col=colors[i])}

Any help would be great thanks!

Answer 1

The problem is that with each call to lines() , you are applying the same colour. To prevent this, you would want to iterate over a vector of colours each time you call lines() . Note that you are actually overwriting lines three times here since you are iterating through Data$Species -- you probably intended unique(Data$Species) .

But as per @Iris's comment, you can do this more easily using ggplot2 :

require(ggplot2)
ggplot(data = Data, aes(x = Transect, y = Count, group = Species)) +
    xlab("Transect Number") + ylab("Total Number") +
    geom_line(aes(color = Species)) 

Answer 2

Short answer is look at ggplot2 as that's far superior than using plot. Just to see the above working, here's a working example (your code slightly modified):

tt <- "Species Count Transect
Cod     25    1
Cod     36    2
Cod     45    3
Haddock 12    1
Haddock 23    2
Haddock 34    3"

Data <- read.table(text=tt,header = T)
xrange <- range(Data$Transect)
ymax <- max(Data$Count)

my.levels <- levels(Data$Species)
my.colors<- rainbow(length(my.levels))

plot(xrange,
     y=c(0,ymax+10),
     yaxs = "i",
     type="n",
     las=1,
     xlab="Transect Number",
     ylab="Total Number")

for (i in 1:length(my.levels))
{
    species <- subset(Data, Species==my.levels[i]) 
    lines(species$Transect, species$Count, type="o",lwd=2,lty=1,pch=NA, col = my.colors[i])
}

When executed will plot: