R – ggplot2: add line for average per group

ggplot2r

library(ggplot2)

orderX <- c("A" = 1, "B" = 2, "C" = 3)
y <- rnorm(20)
x <- as.character(1:20)
group <- c(rep("A", 5), rep("B", 7), rep("C", 5), rep("A", 3))
df <- data.frame(x, y, group)
df$lvls <- as.numeric(orderX[df$group])

ggplot(data = df, aes(x=reorder(df$x, df$lvls), y=y)) + 
geom_point(aes(colour = group)) + 
geom_line(stat = "hline", yintercept = "mean", aes(colour = group))

I want to create a graph like this:
graph with averages for each group

This does work, when I do not need to reorder the values of X, however, when I do use reorder, it doesn't work anymore.

Best Answer

From your question, I don't this df$x is relevant to your data at all, especially if you can re-order it. How about just using group as x, and jitter the actual x position to separate the points:

ggplot(data=df, aes(x=group,y=y,color=group)) + geom_point() +
geom_jitter(position = position_jitter(width = 0.4)) +
geom_errorbar(stat = "hline", yintercept = "mean",
  width=0.8,aes(ymax=..y..,ymin=..y..))

I have used errorbar instead of h_line (and collapsed the ymax and ymin to y) since hline is complex. If anyone has a better solution to that part, I'd love to see.

alt text

update

If you want to preserve the order of X, try this solution (with modified X)

df$x = factor(df$x)

ggplot(data = df, aes(x, y, group=group)) + 
facet_grid(.~group,space="free",scales="free_x") + 
geom_point() + 
geom_line(stat = "hline", yintercept = "mean")

alt text

Related Solutions

R – How to set limits for axes in ggplot2 R plots

Basically you have two options

scale_x_continuous(limits = c(-5000, 5000))

coord_cartesian(xlim = c(-5000, 5000))

Where the first removes all data points outside the given range and the second only adjusts the visible area. In most cases you would not see the difference, but if you fit anything to the data it would probably change the fitted values.

You can also use the shorthand function xlim (or ylim), which like the first option removes data points outside of the given range:

+ xlim(-5000, 5000)

For more information check the description of coord_cartesian.

The RStudio cheatsheet for ggplot2 makes this quite clear visually. Here is a small section of that cheatsheet:

Distributed under CC BY.

R – Creating a line chart in r for the average value of groups

You can also use the dplyr package to aggregate the data:

library(dplyr)
mean_data <- group_by(data, gender, week) %>%
             summarise(motivation = mean(motivation, na.rm = TRUE))

You can use na.omit() to get rid of the NA values as follows:

library(ggplot2)
ggplot(na.omit(mean_data), aes(x = week, y = motivation, colour = gender)) +
  geom_point() + geom_line()

There is no need here to explicitly use the group aesthetic because ggplot will automatically group the lines by the categorical variables in your plot. And the only categorical variable you have is gender. (See this answer for more information).

Best Answer

Related Solutions

R – How to set limits for axes in ggplot2 R plots

R – Creating a line chart in r for the average value of groups

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