ggplot2 (version 1.0.1)

geom_hline: Horizontal line.


This geom allows you to annotate the plot with horizontal lines (see geom_vline and geom_abline for other types of lines).


geom_hline(mapping = NULL, data = NULL, stat = "hline",
  position = "identity", show_guide = FALSE, ...)


The aesthetic mapping, usually constructed with aes or aes_string. Only needs to be set at the layer level if you are overriding the plot defaults.
A layer specific dataset - only needed if you want to override the plot defaults.
The statistical transformation to use on the data for this layer.
The position adjustment to use for overlapping points on this layer
should a legend be drawn? (defaults to FALSE)
other arguments passed on to layer. This can include aesthetics whose values you want to set, not map. See layer for more details.


[results=rd,stage=build]{ggplot2:::rd_aesthetics("geom", "hline")} p <- ggplot(mtcars, aes(x = wt, y=mpg)) + geom_point()

p + geom_hline(aes(yintercept=mpg)) p + geom_hline(yintercept=20) p + geom_hline(yintercept=seq(10, 30, by=5))

# With coordinate transforms p + geom_hline(aes(yintercept=mpg)) + coord_equal() p + geom_hline(aes(yintercept=mpg)) + coord_flip() p + geom_hline(aes(yintercept=mpg)) + coord_polar()

# To display different lines in different facets, you need to # create a data frame. p <- qplot(mpg, wt, data=mtcars, facets = vs ~ am) <- data.frame(z = 1:4, vs = c(0,0,1,1), am = c(0,1,0,1)) p + geom_hline(aes(yintercept = z),

geom_vline for vertical lines, geom_abline for lines defined by a slope and intercept, geom_segment for a more general approach


There are two ways to use it. You can either specify the intercept of the line in the call to the geom, in which case the line will be in the same position in every panel. Alternatively, you can supply a different intercept for each panel using a data.frame. See the examples for the differences