connect points in ggplot2 with different line type

Question

"a" is a data frame.

set.seed(2)
a<-data.frame(group= rep(c("A","B","C"),each=4),factor=rep(c(1,1,2,2),3),
              model=rep(c("old","new"),6),mean=runif(12),sd=runif(12)/10)

>a
           group factor model      mean          sd
        1      A      1   old 0.1848823 0.076051331
        2      A      1   new 0.7023740 0.018082010
        3      A      2   old 0.5733263 0.040528218
        4      A      2   new 0.1680519 0.085354845
        5      B      1   old 0.9438393 0.097639849
        6      B      1   new 0.9434750 0.022582546
        7      B      2   old 0.1291590 0.044480923
        8      B      2   new 0.8334488 0.007497942
        9      C      1   old 0.4680185 0.066189876
        10     C      1   new 0.5499837 0.038754954
        11     C      2   old 0.5526741 0.083688918
        12     C      2   new 0.2388948 0.015050144

I want to draw a "mean±sd" line graph with ggplot2. My aim is to draw a picture (x-axis is "group", y-axis is "mean±sd", different "factor" should have different color, different "model" should have different connecting line type (old model is dashed line, new model is solid line))

I use following code:

library("ggplot2")
pd <- position_dodge(0.1)  #The errorbars overlapped, so use position_dodge to move 
                           #them horizontally 
plot<-ggplot(a, aes(x=group, y=mean, colour=as.factor(factor), linetype=model)) + 
    geom_errorbar(aes(ymin=mean-sd, ymax=mean+sd), width=.1, position=pd) +
    geom_point(position=pd, size=3, shape=21, fill="white") + # 21 is filled circle
    xlab("Groups") +
    ylab("Power") +
    geom_line(position=pd) +
    scale_linetype_manual(values = c(new = "solid", old = "dashed"))

but "mean±sd" should all be solid lines, and connection between points should be added. Actually I want it to be like this:

Can you give me some advice, thank you!

Answer 1

I'd suggest adding a new grouping variable:

a$group2 <- paste(a$factor, a$model, sep="_")

Then remove linetype from ggplot() and modify geom_line() :

    ggplot(a, aes(x = group, y = mean, colour = as.factor(factor))) + 
      geom_errorbar(aes(ymin = mean-sd, ymax = mean+sd), 
                    width = .1, position = pd) +
      geom_point(position = pd, size = 3, shape = 21, fill = "white") + 
      xlab("Groups") +
      ylab("Power") +
      geom_line(aes(x = group, y = mean, colour = as.factor(factor), 
                    group = group2, linetype = model)) +
      scale_linetype_manual(values = c(new = "solid", old = "dashed"))