Force error bars to be in the middle of bar

Question

I\'m using R and ggplot2 to plot a pretty basic bar graph with error bars, but I\'m having trouble forcing them to be in the center of the bars that I create.

My co

Answer 1

Your bars are 10.8 units wide (12 units each, times 0.9 for the gap), so try:

position = position_dodge(10.8*2)

in your geom_errorbar call

Answer 2

While @jeremycg's answer is correct (+1 for obscure knowledge of ggplot theme system), it's more of a side-effect than a solution.

Let's just think for a moment of the typical use case scenario for a bar chart. Generally we would use a bar chart when we are trying to present data that are:

• Discrete by Continuous

Right now, we have data that are:

• Continuous by Continuous

A dot plot would be more appropriate for this data type. But we can see that it looks a bit ridiculous because our data are not truly continuous.

ggplot(df, aes(Time,CellCount, color = Type)) + 
  geom_point(stat="identity") + 
  geom_errorbar(aes(
    ymin = CellCount - Error, 
    ymax = CellCount + Error),   
    width = 0.9)

For a presentation of this nature, one ought to use a categorical variable for their x-coordinate.

This can be accomplished by pre-processing your variable, Time, as a factor, or by calling the variable as.factor in the aesthetic string (aes).

ggplot(df, aes(
    x=as.factor(Time), # as.factor() makes this a discrete scale
    y = CellCount, 
    fill = Type)) +
  geom_bar(stat = "identity", position = "dodge") +
  geom_errorbar(aes(
    ymin = CellCount - Error, 
    ymax = CellCount + Error),   
    width = 0.9, 
    position = position_dodge(width = 0.9)) + # now you can use it
  labs(x= "Time (h)", y = "Cell count") +
  scale_fill_discrete(labels = c("Anirridia", "Control"))