Copying and modifying a default theme

Question

I would like to create a new theme for ggplot that is based on theme_bw().

I imagine the following steps are necessary (in pseudocode):

1. Make a copy of theme_bw(): theme_new() <- theme_bw()
2. Modify the copy: theme_update(axis.title.x = theme_text(family = base_family, size = base_size, vjust = 0.5))

Any advice on how to implement this will be very much appreciated!

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Edit: @Andrie, I modified your answer for my needs:

theme_new <- theme_set(theme_bw())
theme_new <- theme_update(axis.title.x = theme_text(family = base_family, size = base_size, vjust = 0.5))

However, I get the following error:

ggplot(mtcars, aes(factor(cyl))) + geom_bar()

Error in match(gparname, names(gpars)) : object 'base_size' not found

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Edit: 31/10/2017, answer provided by @Andrie works just fine. R version 3.4.1, ggplot2_2.2.1

Answer 1

Your code just needs a few small changes to work (mainly removing brackets and adding brackets at the right places)

theme_new <- theme_set(theme_bw())

theme_new <- theme_update(
    panel.background = element_rect(fill="lightblue"))

ggplot(mtcars, aes(factor(cyl))) + geom_bar()

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Reference:

• CRAN: extending-ggplot2
• Tidyverse: themes
• GitHub: New-theme-system