When using guide = guide_legend(...) to change non-angle parameters of label.theme or title.theme, an error is generated due to non-NULL value for angle.
Here are examples trying to set face, without setting angle:
library(ggplot2)
ggplot(iris, aes(x = Sepal.Length, y = Petal.Length, color = Species)) +
geom_point() +
scale_color_discrete(guide = guide_legend(label.theme = element_text(face = "italic")))
#> Error in element_grob.element_text(element = label.theme, label = label, : Text element requires non-NULL value for 'angle'.
ggplot(iris, aes(x = Sepal.Length, y = Petal.Length, color = Species)) +
geom_point() +
scale_color_discrete(guide = guide_legend(title.theme = element_text(face = "italic")))
#> Error in element_grob.element_text(guide$title.theme %||% calc_element("legend.title", : Text element requires non-NULL value for 'angle'.(reprex inserts an 'empty plot placeholder' here, despite the code above errors...)
Trying to set size, hjust or vjust without setting angle leads to the same error.
To change any non-angle parameters, we need to set angle as well. E.g.:
ggplot(iris, aes(x = Sepal.Length, y = Petal.Length, color = Species)) +
geom_point() +
scale_color_discrete(guide = guide_legend(label.theme = element_text(face = "italic", angle = 0)))
In contrast, there is no need to explicitly set any of the other NULL arguments in element_text when setting angle only:
ggplot(iris, aes(x = Sepal.Length, y = Petal.Length, color = Species)) +
geom_point() +
scale_color_discrete(guide = guide_legend(
label.theme = element_text(angle = -5)))
ggplot(iris, aes(x = Sepal.Length, y = Petal.Length, color = Species)) +
geom_point() +
scale_color_discrete(guide = guide_legend(
title.theme = element_text(angle = 5))) 
When using
guide = guide_legend(...)to change non-angleparameters oflabel.themeortitle.theme, an error is generated due to non-NULLvalue forangle.Here are examples trying to set
face, without settingangle:(
reprexinserts an 'empty plot placeholder' here, despite the code above errors...)Trying to set
size,hjustorvjustwithout settingangleleads to the same error.To change any non-
angleparameters, we need to setangleas well. E.g.:In contrast, there is no need to explicitly set any of the other
NULLarguments inelement_textwhen settingangleonly:ggplot(iris, aes(x = Sepal.Length, y = Petal.Length, color = Species)) + geom_point() + scale_color_discrete(guide = guide_legend( title.theme = element_text(angle = 5)))