remove legend title in ggplot

This works too and also demonstrates how to change the legend title:

ggplot(df, aes(x, y, colour=g)) +
  geom_line(stat="identity") + 
  theme(legend.position="bottom") +
  scale_color_discrete(name="")

You were almost there : just add theme(legend.title=element_blank())

ggplot(df, aes(x, y, colour=g)) +
  geom_line(stat="identity") + 
  theme(legend.position="bottom") +
  theme(legend.title=element_blank())

This page on Cookbook for R gives plenty of details on how to customize legends.

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