Width of error bars in line plot using ggplot2

Below is a reproducible example using random data. The fix to the problem is to multiply the width by the number of classes/factors that you have. In the plot below, since I used three factors, using a width of 3 fixes the problem. ggplot2 seems to calculate the relative width by the number of data points in your dataset, rather than the numeric values on the x-axis. This is (IMO) a bug.

library(ggplot2)library(grid)#plot with factorshod <- data.frame(h = c(1:24,1:24,1:24), mean = 1:(24*3) + runif(24*3, 0, 5),ci = runif(24*3, 0, 2), t = c(rep("a",24),rep("b",24),rep("c",24)))pd <- position_dodge(0.3)  dayplot <- ggplot(hod, aes(x=h, y=mean, colour=as.factor(t),group=as.factor(t))) +     geom_line(position=pd, size=1) +    geom_errorbar(aes(ymin=mean-ci, ymax=mean+ci),                  width=1,                  size=0.5,                  position=pd) +    geom_point(position=pd, shape=21, size=1, fill="white") +    scale_x_continuous(limits=c(-0.5,23.5),                       breaks=c(0:8*3),                       labels=ifelse(                              c(0:8*3) < 10,                              paste('0',c(0:8*3),':00',sep=''),                              paste(c(0:8*3),':00',sep='')                              )                       ) +    xlab("Hour of day") +    theme_minimal() +     theme(plot.margin = unit(c(1,0,1,1), "cm"),           axis.title.x = element_text(vjust=-1),          axis.title.y = element_text(angle=90, vjust=0),          legend.margin = unit(c(0), "cm"),          legend.key.height = unit(c(0.9), "cm"),          panel.grid.major = element_line(colour=rgb(0.87,0.87,0.87)),          panel.grid.minor = element_blank(),          plot.background = element_rect(fill = rgb(0.97,0.97,0.97), linetype=0)    )print(dayplot)#plot without factorshod <- data.frame(h = c(1:24,1:24,1:24), mean = 1:(24) + runif(24, 0, 5),ci = runif(24, 0, 2))pd <- position_dodge(0.3)  dayplot <- ggplot(hod, aes(x=h, y=mean)) +     geom_line(position=pd, size=1) +    geom_errorbar(aes(ymin=mean-ci, ymax=mean+ci),                  width=1,                  size=0.5,                  position=pd) +    geom_point(position=pd, shape=21, size=1, fill="white") +    scale_x_continuous(limits=c(-0.5,23.5),                       breaks=c(0:8*3),                       labels=ifelse(                              c(0:8*3) < 10,                              paste('0',c(0:8*3),':00',sep=''),                              paste(c(0:8*3),':00',sep='')                              )                       ) +    xlab("Hour of day") +    theme_minimal() +     theme(plot.margin = unit(c(1,0,1,1), "cm"),           axis.title.x = element_text(vjust=-1),          axis.title.y = element_text(angle=90, vjust=0),          legend.margin = unit(c(0), "cm"),          legend.key.height = unit(c(0.9), "cm"),          panel.grid.major = element_line(colour=rgb(0.87,0.87,0.87)),          panel.grid.minor = element_blank(),          plot.background = element_rect(fill = rgb(0.97,0.97,0.97), linetype=0)    )print(dayplot)

I have managed to solve a similar issue. In my case I wanted to set both horizontal and vertical errorbar heads to the same size - regardless of the aspect ratio of the plot.

Based on the original posted code:

f <- ggplot_build(dayplot)f$plot$layers[[5]]$geom_params$width  <- 0.02 * diff(f$layout$panel_params[[1]]$x.range)f$plot$layers[[6]]$geom_params$height <- 0.02 * diff(f$layout$panel_params[[1]]$y.range)dayplot <- f$plot

This will set the errorbar head to 2% of the axis range. Maybe could solve your issue.