How can I add a legend

General Usage
1

Hi!

I plot a data, for example y = [1, 2, 3, 999, 34, 35, 34, 23, 345, 234, 23] and with classes=[1, 2, 1, 2, 3, 1, 2, 3, …]
Then I write:
plot(x, y, linecolor = classes)
So I get a plot with one line with three different colours (like a piecewise line).

The question is how can label three different colours since when I use plot(label = [“1” “2” “3”]), the plot only shows “1” since there is actually one line. Thanks a lot!

1 Like
2

Welcome @bayerndd,

which plotting package are you using and please check

1 Like
3

Hi! I am using Plots only

4

I think, what you want is not possible in a more or less single plot command.
The way to go is to decompose the single line into pieces for each color and plot them successively into the same plot.
Here is how I solved it:

using Plots 

function decompose(classes,c)
	r1=falses(length(classes)+1)
	r2=falses(length(classes)+1)
	b=0
	for i in 1:length(classes)
		if classes[i]==c
			if b==0
				b=1
				r1[i]=true
				r1[i+1]=true
			else
				b=0
				r2[i]=true
				r2[i+1]=true
			end
		else
			i>1&&!r1[i-1] ? r1[i]=false : nothing
			i>1&&!r2[i-1] ? r2[i]=false : nothing
		end
	end
	(r1,r2)
end

x=1:11   #x-axis
y = [1, 2, 3, 999, 34, 35, 34, 23, 345, 234, 23]  #y-axes 11 points
classes=[1, 2, 1, 2, 3, 1, 2, 3, 2, 3]  # 11 points define 10 lines => 10 color entries

yp1=Array{Union{Missing, Int64}}(undef,length(y))
yp2=Array{Union{Missing, Int64}}(undef,length(y))

p=plot()
for c in sort(unique(classes))
	#global p #not needed
	yp1.=missing
	yp2.=missing
	yp1[decompose(classes,c)[1]]=y[decompose(classes,c)[1]]
	yp2[decompose(classes,c)[2]]=y[decompose(classes,c)[2]]
	plot!(p,x,yp1,linecolor=c,label=c)
	plot!(p,x,yp2,linecolor=c,label=nothing)
end
display(p)

out

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