change line color in ggplot

Question

I have this data frame:

dftt <- data.frame(values = runif(11*4,0,1),
                 col = c(rep(2,4),
                         rep(1,4),
                         rep(5,9*4)),
                 x= rep(1:4, 11*4),
                 group=rep(factor(1:11), each=4)
                 )

> head(dftt)
     values col x group
1 0.2576930   2 1     1
2 0.4436522   2 2     1
3 0.5258673   2 3     1
4 0.2751512   2 4     1
5 0.5941050   1 1     2
6 0.7596024   1 2     2

I plot it like this:

ggplot(dftt, aes(x=x, y=values, group=group, color=col)) + geom_line() 

How can I change the line colors, I want the first two lines to be black and red (in the above plot they are both black) and the remaining lines to be gray (they are light blue)?

Answer 1

Is there a reason why you even try adding colors via col? It seems to me like this is strange as col has fewer values than group. If you just want to color the groups, this would be the correct way:

  ggplot(dftt, aes(x=x, y=values, group=group, color=group)) + 
  geom_line() +
  scale_color_manual(values = c("black",
                                "red",
                                rep("gray", 9)))

Answer 2

Covert your col column to a factor and then add scale_color_manual to your plot function.

library(ggplot2)
dftt$col<-as.factor(dftt$col)

ggplot(dftt, aes(x=x, y=values, group=group, color=col)) + geom_line(size=1.2) +
  scale_color_manual(values=c( "black", "red", "blue"))

You may need to rearrange the color scale to match your choice of color (1,2 and 5)