Horizontal line with different colours

Question

How I can modify this code to have different colors for lines (for example Black, red, green)

library(ggplot2)

    lt <- data.frame(yint = c(200, 250, 210, 215, 279, 280),
                     grp  = factor(c(1, 1, 2, 2, 3, 3),
                                   levels = 1:3,
                                   labels = c("Group 1", "Group 2", "Group 3")))


    ggplot(mtcars, aes(mpg, disp)) + 
          geom_point(aes(colour=factor(vs), 
          fill = factor(vs)), shape=21, size = 4) + 
          scale_fill_manual(values=c("blue", "pink")) + 
          scale_colour_manual(values=c("black", "black"))+
          geom_hline(data = lt,
                     mapping = aes(yintercept = yint, linetype = grp))

I tried to use this function buT I got the error

ggplot(DataSet, aes(AGE, RESULT)) + 
      geom_point(aes(colour=PATIENT.SEX, 
      fill = PATIENT.SEX), shape=21, size = 1.4) + 
      scale_fill_manual(values=c("hotpink", "skyblue2")) + 
      scale_colour_manual(values=c("hotpink", "skyblue2"))+  
      ylab("Potassium (mmol/L) ")+xlab("Age (month) ")+ggtitle("Alberta observations")+theme_bw()+
      theme(plot.title = element_text(lineheight=.8, face="bold",size=13))+
      theme(axis.text=element_text(size=12),axis.title=element_text(size=12,face="bold"))+
      theme(panel.border = element_blank(), panel.grid.major = element_blank(),
      panel.grid.minor = element_blank(), axis.line = element_line(colour = "black"))+
      geom_hline(data = lt,
                 mapping = aes(yintercept = yint,linetype = RI),colour
=c("blue","blue", "red", "red", "black","black" ))

Answer 1

A solution is to modify the scale_color_manual call. Set the values and the limits for the factor levels for vs (as already done in your post) and for the three group levels. In the example below I've set the color for the factor(vs) to black for both levels, as was done in the original post, and then set the colors for Group 1, Group 2, and Group 3 as purple, green, and yellow.

library(ggplot2)

lt <- data.frame(yint = c(200, 250, 210, 215, 279, 280),
                 grp  = factor(c(1, 1, 2, 2, 3, 3),
                               levels = 1:3,
                               labels = c("Group 1", "Group 2", "Group 3")))


ggplot(mtcars, aes(mpg, disp)) + 
      geom_point(aes(colour=factor(vs), fill = factor(vs)), shape=21, size = 4) + 
      scale_fill_manual(values=c("blue", "pink")) + 
      geom_hline(data = lt,
                 mapping = aes(yintercept = yint, linetype = grp, color = grp)) +
      scale_color_manual(name   = "",
                         values = c("black", "black", "Purple", "Green", "Yellow"),
                         limits = c(0, 1, "Group 1", "Group 2", "Group 3"))

Answer 2

One "brute force" option available starting in the current development version of ggplot2, 2.2.1.9000, is to set colors outside of aes. The colors you give either has to be length 1 (all colors the same) or the same length as the dataset used in that layer.

In your example you have 6 rows in your dataset to make 6 horizontal lines so I give 6 colors.

If using this method you have to be careful to get the colors matched up with the appropriate row in the dataset. In your real use case you could consider adding the colors to the dataset to keep organized.

ggplot(mtcars, aes(mpg, disp)) + 
     geom_point(aes(colour=factor(vs), 
                    fill = factor(vs)), shape=21, size = 4) + 
     scale_fill_manual(values=c("blue", "pink")) + 
     scale_colour_manual(values=c("black", "black"))+
     geom_hline(data = lt,
                mapping = aes(yintercept = yint, linetype = grp), 
                color = c("black", "black", "red", "red", "green", "green") )

If you want to put the colors on the linetype legend, you can use guide_legend and override.aes to set legend colors.

ggplot(mtcars, aes(mpg, disp)) + 
     geom_point(aes(colour=factor(vs), 
                    fill = factor(vs)), shape=21, size = 4) + 
     scale_fill_manual(values=c("blue", "pink")) + 
     scale_colour_manual(values=c("black", "black"))+
     geom_hline(data = lt,
                mapping = aes(yintercept = yint, linetype = grp), 
                color = c("black", "black", "red", "red", "green", "green") ) +
     guides(linetype = guide_legend(override.aes = list(color = c("black", "red", "green") ) ) )