# Easily add direct labels to plots using the directlabels package!

This package 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. The main function that the package provides is direct.label(p), which takes a lattice or ggplot2 plot p and adds direct labels:

```install.packages("directlabels")
library(lattice)
library(directlabels)
direct.label(xyplot(jitter(Sepal.Length)~jitter(Petal.Length),iris,groups=Species))
```

• Before emailing me, please search and post on stackoverflow.
• How to avoid overlapping labels? Use a Positioning Method with calc.boxes to compute the label bounding box. For example, smart.grid for scatterplots and last.polygons or last.qp for lineplots.
• Can I increase text size? Yes, but do it before calling Positioning Methods that calculate the label bounding box: direct.label(p, list(cex=2, "last.qp")) for a lineplot p.
• Why are some labels small when using lineplot labeling methods like last.polygons? Because the labels are automatically resized to fit in the plotting area. To increase the text size you can increase the x axis limits as in the lars and ridge examples.
• How to adjust all labels left or right? For example you can use direct.label(p, list(dl.trans(x=x+0.1), "last.qp")) to move labels to the right 0.1cm and then apply last.qp for a lineplot p.
• How about fontface, fontfamily, rot, alpha text parameters? See example(dlcompare).
• How about direct labeling aesthetics other than colour in ggplot2? See example(geom_dl).
• Can I use directlabels to label individual points on scatterplots? The intended purpose of directlabels is to replace a confusing legend (which labels groups of points, not individual points). You may want to try to write your own Positioning Method but be aware that automatic label placement is an NP-hard problem!

## Positioning Methods specify the direct label positions

Direct labeling a plot can be decomposed into 2 steps: calculating label positions, then drawing the labels. For the first step, the directlabels package introduces the concept of the Positioning Method, which is a list that specifies how to transform the data points into labels. For example, with the scatterplot above, the default Positioning Method is smart.grid, which places each label close to the center of the corresponding point cloud. The following diagram shows how the data to plot is converted to standard form column names and positions in centimeters before the Positioning Method is applied:

 ```Petal.Length Sepal.Length Species 1.4 5.1 setosa 1.4 4.9 setosa 1.3 4.7 setosa 1.5 4.6 setosa 1.4 5.0 setosa 1.7 5.4 setosa ... ... ... ``` ``` convert to standard form (cm) ---------------------> direct.label.trellis and drawDetails.dlgrob ``` ``` x y groups 2.021041 3.786670 setosa 2.021041 3.066771 setosa 1.772450 2.346872 setosa 2.269632 1.986922 setosa 2.021041 3.426721 setosa 2.766813 4.866519 setosa ... ... ... ``` ``` calculate label positions with Positioning Method ---------------------> smart.grid ``` ``` x y groups 0.8364451 3.806 setosa 11.2194634 11.418 virginica 8.0289573 7.958 versicolor ```

If default label positions are not satisfactory, you can always specify your own Positioning Method, using the method= argument to direct.label. For example, we can label longitudinal data either on the left or right of the lines:

```install.packages("ggplot2")
library(ggplot2)
data(BodyWeight,package="nlme")
p <- qplot(Time,weight,data=BodyWeight,colour=Rat,geom="line",facets=.~Diet)
direct.label(p,"first.qp")
direct.label(p,"last.qp")
```

first.qp and last.qp are the names of Positioning Methods which place the labels respectively near the first or last points, ensuring that the labels do not overlap and so are readable. To find out which built-in Positioning Methods are appropriate for your plot, check out the Positioning Methods example database.

However, the power of the directlabels system is the fact that you can write your own Positioning Methods, and they can be reused for different plots. So once you write a Positioning Method that works, adding direct labels in everyday plots is as simple as calling direct.label, no matter if you are using lattice or ggplot2.

Recent advances in direct labeled graphics [source]. Invited talk for semin-r, the Paris R user group (2012).

Adding direct labels to plots, Best Student Poster at useR 2011, attempts to motivate the package and explain how it works [source]. Notably, the "Optimal Labels" section is basically the only documentation of how to implement the qp.labels Positioning Method. The details of the "Modular package design" section have changed in version 2.0. Rather than calling label.positions the first time the plot is printed, we now draw a dlgrob whose drawDetails method calculates label positions every time the plot window is resized/redrawn.

semin-r, 15 oct 2009. "Visualizing multivariate data using lattice and direct labels" with R code examples. Note that the latticedl package used in these slides is obsolete, so please use the directlabels package instead.

Blog reviews: learnr 2010, Karl Broman 2011.

The labcurve function in the Hmisc package provides some similar functionality.

More examples of directlabels on the R Graphical Manual.