Naming each panel using a title and a segment below x-axis

[jarjarbinks]

I have the same problem as in this Stackoverflow issue.

However, I want the segment and the title to be placed below the x-axis, not above the y-axis.
I'm using the following code to place the panel titles in the x-axis:

facet_grid('. ~group, scales="free", switch = "x") + 

But I dont know how to place a segment above the text. I tried doing:

 + annotate("segment",x=Inf,xend=-1, y=-1,yend=Inf,color="black",lwd=1)

but the horizontal line went inside the ggplot at y=-1 instead of outside the box.

Hope someone can help me with this. Thank you!

[nirgrahamuk]

I came up with this.

my.df <- data.frame(mean = c(0.045729661, 0.030416531, 0.043202944, 0.025600973, 0.040526913, 0.046167044, 0.029352414, 0.021477789, 0.027580529, 0.017614864, 0.020324659, 0.027547972, 0.0268722, 0.030804717, 0.021502093, 0.008342398, 0.02295506, 0.022386184, 0.030849534, 0.017291356, 0.030957321, 0.01871551, 0.016945678, 0.014143042, 0.026686185, 0.020877973, 0.028612298, 0.013227244, 0.010710895, 0.024460647, 0.03704981, 0.019832982, 0.031858501, 0.022194059, 0.030575241, 0.024632496, 0.040815748, 0.025595652, 0.023839083, 0.026474704, 0.033000706, 0.044125751, 0.02714219, 0.025724641, 0.020767752, 0.026480009, 0.016794441, 0.00709195), std.dev = c(0.007455271, 0.006120299, 0.008243454, 0.005552582, 0.006871527, 0.008920899, 0.007137174, 0.00582671, 0.007439398, 0.005265133, 0.006180637, 0.008312494, 0.006628951, 0.005956211, 0.008532386, 0.00613411, 0.005741645, 0.005876588, 0.006640122, 0.005339993, 0.008842722, 0.006246828, 0.005532832, 0.005594483, 0.007268493, 0.006634795, 0.008287031, 0.00588119, 0.004479003, 0.006333063, 0.00803285, 0.006226441, 0.009681048, 0.006457784, 0.006045368, 0.006293256, 0.008062195, 0.00857954, 0.008160441, 0.006830088, 0.008095485, 0.006665062, 0.007437581, 0.008599525, 0.008242957, 0.006379928, 0.007168385, 0.004643819), parent.origin = c("paternal", "paternal", "paternal", "paternal", "paternal", "paternal", "maternal", "maternal", "maternal", "maternal", "maternal", "maternal", "paternal", "paternal", "paternal", "paternal", "paternal", "paternal", "maternal", "maternal", "maternal", "maternal", "maternal", "maternal", "maternal", "maternal", "maternal", "maternal", "maternal", "maternal", "paternal", "paternal", "paternal", "paternal", "paternal", "paternal", "maternal", "maternal", "maternal", "maternal", "maternal", "maternal", "paternal", "paternal", "paternal", "paternal", "paternal", "paternal"), group = c("F1r:M", "F1r:M", "F1r:M", "F1r:M", "F1r:M", "F1r:M", "F1r:M", "F1r:M", "F1r:M", "F1r:M", "F1r:M", "F1r:M", "F1r:F", "F1r:F", "F1r:F", "F1r:F", "F1r:F", "F1r:F", "F1r:F", "F1r:F", "F1r:F", "F1r:F", "F1r:F", "F1r:F", "F1i:M", "F1i:M", "F1i:M", "F1i:M", "F1i:M", "F1i:M", "F1i:M", "F1i:M", "F1i:M", "F1i:M", "F1i:M", "F1i:M", "F1i:F", "F1i:F", "F1i:F", "F1i:F", "F1i:F", "F1i:F", "F1i:F", "F1i:F", "F1i:F", "F1i:F", "F1i:F", "F1i:F"), replicate = c(1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6, 1, 2, 3, 4, 5, 6))

library(ggplot2)
my.df$group_longer <- paste0("  ",my.df$group,"  ")

p1 <- ggplot(data = my.df, aes(factor(replicate), color = factor(parent.origin)))
p1 <- p1 + geom_boxplot(aes(fill = factor(parent.origin), 
                            lower = mean - std.dev, upper = mean + std.dev, middle = mean, ymin = mean - 3 * std.dev, ymax = mean + 3 * std.dev), position = position_dodge(width = 0), width = 0.5, alpha = 0.5, stat = "identity") + 
  facet_wrap(~group_longer,ncol=4, scales="free", strip.position = "bottom",labeller = label_bquote(underline(.(group_longer))))+ 
  scale_fill_manual(values = c("red", "blue"), labels = c("maternal", "paternal"), name = "parental allele") + 
  scale_colour_manual(values = c("red", "blue"), labels = c("maternal", "paternal"), name = "parental allele")
p1 <- p1 + 
  theme(panel.grid.major = element_blank(), panel.grid.minor = element_blank(),
        panel.background = element_rect(fill = "white", colour = "white"), legend.position = "none") +
  theme(strip.background = element_rect(fill = "white")) + 
  theme(strip.placement = "outside")
p1

[jarjarbinks]

Thank you for the reply, but I need the horizontal line above the title name and it should span the entire x-axis for that panel. At the moment, the solution seems to be underlining the title of each panel. Should be something like this, but below each

panel:

But still thank u for this.