(This example is inspired by and derived from this thread on the mailing list. This can be useful since the space for facets is not expanded to guarantee that the entire label is visible. The following is an example of a labeller which wraps long labels at a fixed character count so that they take up less space. Multiple factors occur with formula of the type. A list of calls, each element of which is one label A labeller function accepts a data frame of labels (character vectors) containing one column for each factor.A list of expressions, each element of which is one label.A factor whose character representation is the labels.All four built in labellers return different structures, all of which are apparently acceptable. The output of labeller varies quite a lot. What gets passed as value need not be unique because levels can be repeated in the case of nested faceting see the last example. If the faceting variable is a character variable or a numeric variable, then value is a simple vector of the (not necessarily unique, but ordered) values of the faceting variable. If the faceting variable is a factor, this is a factor including the used levels (note that there may be additional levels to the factor which are not part of the faceting, but were levels of the factor to begin with thus it is the character representation of the factor which is relevant, not the levels). value is the ordered (not necessarily unique) values of the facets. variable is a length 1 character vector with the name of the variable which is being faceted on. The structure of a labeller is a function that takes two arguments: variable and value. P + facet_grid( drv ~ cyl, labeller =label_bquote( expr = alpha)) The purpose it to allow the levels of the factor to be substituted into a given expression (which is provided to the generator).įor examples, we will use the same mpg2 data set as is used in the examples in 7.2 of the ggplot book as well as the same base plot. ![]() label_bquote: This labeller is different that the others in that it is not itself a labeller, but a function that creates a valid labeller.label_parsed: This labeller takes the character representation of the facet levels and passes them to parse so that they may be typeset as mathematics as per plotmath (see help(plotmath)).label_both: This labeller prepends the name of the variable being faceted on to the factor level, separated by a colon and a space. ![]() This labeller uses the direct character representation of the levels of the factor as what appears in the facet label. The purpose of the labeller argument is to give a way to transform the levels of a factor which a plot is being faceted on before they appear on the plot itself. It is based on the structure of the source code and functions and is not guaranteed to work or be correct in future versions. This documentation is descriptive, not proscriptive. This page is meant to try and document it. See Generic labeller function for more information.įacet_grid has an option, labeller, which is not well documented as to what it does and how it is to be used. ![]() Labellers taking variableand value arguments, like the examples on this page, are now deprecated. Note: The ggplot2 wiki is no longer maintained, please use the ggplot2 website instead!
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