ggplot2: axis line at 0 with negative datapoints - r

Question

I am doing boxplot with positive and negative data and would like to have the axis at y=0.
adding a line afterwards is not elegant since the line would be on to of the boxes and not behind them.
(the goal is to have the line at y=0 black, while the lines at 1 and -1 should be gray)
In addition I would like to have only the axis lines. I therefore used
axis.line=element_line()
,panel.border = element_blank()
in the theme. however the vertical line goes above 1, which does not look good (my data is by definition between -1 and 1).
here is the code:
require (ggplot2)
theme_jack <- function (base_size = 10, base_family = "") {
theme_bw(base_size = base_size, base_family = base_family) %+replace%
theme(
title = element_text(size = 12)
,axis.title.x = element_text(colour = "white", size=0)
,axis.title.y = element_text(size=12, angle=90)
,axis.text.x=element_text(size=8)
,panel.grid.major = element_line(colour = "grey")#,
,axis.line=element_line()
,panel.border = element_blank()
,panel.grid.minor = element_blank()
,panel.grid.major.x = element_blank()
,legend.position = "none"
)
}
theme_set(theme_jack())
datatest2=structure(list(datatest2.genotype = structure(c(1L, 1L, 5L, 5L,
1L, 5L, 5L, 5L, 1L, 5L, 1L, 5L, 1L, 5L, 5L, 1L, 1L, 1L, 5L, 5L,
1L, 1L, 1L, 5L, 1L, 1L, 5L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 6L, 6L,
6L, 6L, 6L, 6L), .Label = c("CS_d42-chG80", "CS_G_c380cha", "CS_Gd42-chG80",
"PKC_CS", "PKC_d42-chG80", "PKC_G_c380cha", "PKC_Gd42-chG80"), class = "factor"),
datatest2.score = c(0.8882, -0.3775, -0.4053, 0.1962, 0.9982,
0.5627, -0.4865, 0.7267, 0.3276, 0.5017, 0.9731, 0.1525,
0.7857, 0.6121, 0.8508, 0.1311, -0.2457, 0.8848, -0.1254,
0.1047, -0.2715, 0.7189, 0.4115, 0.9704, -0.8328, -0.1301,
0.9756, 0.2317, 0.4297, 0.9967, 0.6423, 0.8516, 0.3386, 0.5208,
0.9148, 0.2539, 0.8581, 0.5621, 0.5969, 0.7435)), .Names = c("genotype",
"score"), row.names = c(NA, 40L), class = "data.frame")
p=ggplot(datatest2, aes(x=factor(genotype),y= score))
plot=p+ geom_boxplot()+ labs(x="genotype",y="PI during final test")+
scale_fill_grey(start = 0.9, end = 0.9)+ ##allow good bw prints
scale_y_continuous(minor_breaks=NULL,breaks = seq(-1 , 1, 1) )
plot

Answer 1

Try the expand argument to `scale_y_continuous. Replace the final section with this and you should get something closer to what you want. You may have to experiment with the values below.
p = ggplot(datatest2, aes(x = factor(genotype), y = score))
plot = p+ geom_boxplot()+ labs(x = "genotype",
y = "PI during final test")+
scale_fill_grey(start = 0.9, end = 0.9)+ ##allow good bw prints
scale_y_continuous(expand = c(0,0.005),
minor_breaks = NULL,
breaks = seq(-1 , 1, 1) ) +
theme()
plot