Adding legend to a single line chart using ggplot

Question

I just try to make a line chart and add a legend to it using ggplot in R. The following is my code.

ggplot(mtcars, aes(x=mpg, y=wt)) + geom_line(stat = "identity") + scale_fill_identity(name = "", guide = "legend", labels = c("myLegend"))

and I got the following:

The legend is not shown in the plot and what I want is the following:

which I plot using Matlab. Could anyone tell me how to do it in R? Thank you so much!!

Michael Ohlrogge · Accepted Answer · 2017-05-07 02:55:14Z

8

You plot is not showing a legend, because there are no aesthetics mapped to the line. Basically, ggplot sees no reason to add a legend as there's only one line.

A simple way to get a legend is to map the line type to a character string:

ggplot(mtcars, aes(x=mpg, y=wt, lty = 'MyLegend')) + geom_line()

You can have a look at ?scale_linetype for information on how to modify tthat legend.

For example, use + scale_linetype('MyLegendTitle') to change the legend title.

edited May 7, 2017 at 2:55

Michael Ohlrogge

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answered Sep 5, 2016 at 10:02

Axeman

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