Adding error bars to a line graph with ggplot2 in R

Question

I have three y values corresponding to three x values. I just want to have a line graph between these three dots

g <- c("1","2","3")
i <- c(181.83,178.74,152.02)
df <- data.frame(g,i)
p <- ggplot(df, aes(x=g, y=i)) + geom_line() + geom_point()

Using this I get this:

First of all why does my geom_line() not work? After that I have:

se <- c(22.95,22.72,19.2)
p + geom_errorbar(aes(ymin=se,ymax=se))

And what I get is:

Why are my errorbars not centered around the data points? Why are they smushed to the bottom? Why do they seem horizontal? What can I do to fix this?

You can fix the first problem with adding group = 1 like this ggplot(df, aes(x = g, y = i, group = 1)) + geom_line() + geom_point() — kath
– kath, Commented Mar 23, 2019 at 17:36
Thank you so much! Should I edit out that part of the question because it's resolved? — YarkınErgin
– YarkınErgin, Commented Mar 23, 2019 at 17:46

markus · Accepted Answer · 2019-03-23 19:42:13Z

2

Alright I figured it out: the ymin and ymax arguments are telling where the error line starts and ends quite literally, so you can't just put the real standard error value and expect ggplot2 to figure out where will this error line be centered. So you have to specify it as:

geom_errobar(aes(ymin = i - se, ymax = i + se))

And finally you get:

Hope it helps others as well.

edited Mar 23, 2019 at 19:42

markus

26.5k5 gold badges47 silver badges59 bronze badges

answered Mar 23, 2019 at 18:05

YarkınErgin

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