**Learning R**, and kindly contributed to R-bloggers)

Sometimes it is preferable to label data series instead of using a legend. This post demonstrates one way of using labels instead of legend in a ggplot2 plot.

> library(ggplot2) |

> p <- ggplot(dfm, aes(month, value, group = City, colour = City)) + geom_line(size = 1) + opts(legend.position = "none") |

> p + geom_text(data = dfm[dfm$month == "Dec", ], aes(label = City), hjust = 0.7, vjust = 1) |

The addition of labels requires manual calculation of the label positions which are then passed on to `geom_text()`. If one wanted to move the labels around, the code would need manual adjustment – label positions need to be recalculated..

This problem is easily solved with the help of `directlabels` package by Toby Dylan Hocking that “is an attempt to make direct labeling a reality in everyday statistical practice by making available a body of useful functions that make direct labeling of common plots easy to do with high-level plotting systems such as lattice and ggplot2″.

> install.packages("directlabels", repos = "http://r-forge.r-project.org") |

> library(directlabels) |

The above plot can be reproduced with one line of code.

> direct.label(p, list(last.points, hjust = 0.7, vjust = 1)) |

In addition to several predefined positioning functions, one can also write their own positioning function. For example, placing the rotated labels at the starting values of each series.

> angled.firstpoints <- list("first.points", rot = 45, hjust = 0, vjust = -0.7) > direct.label(p, angled.firstpoints) |

I agree with the author’s conclusion that the `directlabels` package simplifies and makes more convenient the labeling of data series in both `lattice` and `ggplot2`.

Thanks to Baptiste for bringing this package to my attention.

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