why can't I use element_text() in an ifelse()?

Question

How come I can't return an element_text()

> ifelse(TRUE,element_text(size=20),element_text(size=10))
[[1]]
NULL

but I can do this?

> element_text(size=20)
List of 8
 $ family    : NULL
 $ face      : NULL
 $ colour    : NULL
 $ size      : num 20
 $ hjust     : NULL
 $ vjust     : NULL
 $ angle     : NULL
 $ lineheight: NULL
 - attr(*, "class")= chr [1:2] "element" "element_text"

Answer 1

You can just not in the way you're trying to use it:

Here's an example of what I mean:

ggplot(data=PlantGrowth, aes(x=group, y=weight, fill=group)) + 
    geom_boxplot() + 
    theme(legend.text = element_text(size=ifelse(TRUE, 20, 10)))

It has to do with the if else you're using (ifelse) that's vectorized. I think you're after if(){}else{} as in:

ggplot(data=PlantGrowth, aes(x=group, y=weight, fill=group)) + 
    geom_boxplot()+ 
    theme(legend.text = if(TRUE){element_text(size=20)} else {element_text(size=10)})

though I really wouldn't format it this way but kept it to one line to allow comparison to your method.

The problem isn't ggplot2 but your use of ifelse. Check out ?ifelse and the documentation says:

 ‘ifelse’ returns a value with the same shape as ‘test’ which is
 filled with elements selected from either ‘yes’ or ‘no’ depending
 on whether the element of ‘test’ is ‘TRUE’ or ‘FALSE’.

In your question you show the output of element_text(size=10) that does not resemble test in structure.