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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!!
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Adding a legend If you want to add a legend to a ggplot2 chart you will need to pass a categorical (or numerical) variable to color , fill , shape or alpha inside aes . Depending on which argument you use to pass the data and your specific case the output will be different.
You can use the following syntax to change the legend labels in ggplot2: p + scale_fill_discrete(labels=c('label1', 'label2', 'label3', ...))
By specifying legend. position=”none” you're telling ggplot2 to remove all legends from the plot.
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.
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