Superscripts within ggplot2's axis text

Question

I would like to create a graph that has superscripts on the axis instead of displaying unformatted numbers using ggplot2. I know that there are a lot of answers which change the axis label, but not the axis text. I am not trying to change the label of the graph, but the text on the axis.

Example:

x<-c('2^-5','2^-3','2^-1','2^1','2^2','2^3','2^5','2^7','2^9','2^11','2^13')
y<-c('2^-5','2^-3','2^-1','2^1','2^2','2^3','2^5','2^7','2^9','2^11','2^13')
df<-data.frame(x,y)
p<-ggplot()+
  geom_point(data=df,aes(x=x,y=y),size=4)
p

So I would like the x-axis to display the same numbers but without the carrot.

Answer 1

You can provide a function to the labels argument of the scale_x_*** and scale_y_*** functions to generate labels with superscripts (or other formatting). See examples below.

library(jrnoldmisc)
library(ggplot2)

df<-data.frame(x=2^seq(-5,5,2),
               y=2^seq(-5,5,2))

ggplot(df) +
  geom_point(aes(x=x,y=y),size=2)  +
  scale_x_log2(breaks=2^seq(-5,5,2),
               labels=function(x) parse(text=paste("2^",round(log2(x),2))))

ggplot(df) +
  geom_point(aes(x=x,y=y),size=2)  +
  scale_x_continuous(breaks=c(2^-5, 2^seq(1,5,2)),
                     labels=function(x) parse(text=paste("2^",round(log2(x),2))))

ggplot(df) +
  geom_point(aes(x=x,y=y),size=2)  +
  scale_x_log10(breaks=10^seq(-1,1,1),
                labels=function(x) parse(text=paste("10^",round(log10(x),2))))

Answer 2

This can be done with functions scale_x_log2 and scale_y_log2 that can be found in GitHub package jrnoldmisc.

First, install the package.

devtools::install_github("jrnold/rubbish")

Then, coerce the variables to numeric. I wil work with a copy of the original dataframe.

df1 <- df
df1[] <- lapply(df1, function(x){
  x <- as.character(x)
  sapply(x, function(.x)eval(parse(text = .x)))
})

Now, graph it.

library(jrnoldmisc)
library(ggplot2)
library(MASS)
library(scales)

a <- ggplot(df1, aes(x = x, y = y, size = 4)) + 
  geom_point(show.legend = FALSE) +
  scale_x_log2(limits = c(0.01, NA), 
                labels = trans_format("log2", math_format(2^.x)),
                breaks = trans_breaks("log2", function(x) 2^x, n = 10)) +
  scale_y_log2(limits = c(0.01, NA),
                labels = trans_format("log2", math_format(2^.x)),
                breaks = trans_breaks("log2", function(x) 2^x, n = 10))
a + annotation_logticks(base = 2)

Edit.

Following the discussion in the comments, here are the two other ways that were seen to give different axis labels.

1. Axis labels every tick mark. Set limits = c(1.01, NA) and function argument n = 11, an odd number.
2. Axis labels on odd number exponents. Keep limits = c(0.01, NA), change to function(x) 2^(x - 1), n = 11.

Just the instructions, no plots.

The first.

a <- ggplot(df1, aes(x = x, y = y, size = 4)) + 
  geom_point(show.legend = FALSE) +
  scale_x_log2(limits = c(1.01, NA), 
                labels = trans_format("log2", math_format(2^.x)),
                breaks = trans_breaks("log2", function(x) 2^(x), n = 11)) +
  scale_y_log2(limits = c(1.01, NA),
                labels = trans_format("log2", math_format(2^.x)),
                breaks = trans_breaks("log2", function(x) 2^(x), n = 11))
a + annotation_logticks(base = 2)

And the second.

a <- ggplot(df1, aes(x = x, y = y, size = 4)) + 
  geom_point(show.legend = FALSE) +
  scale_x_log2(limits = c(0.01, NA), 
               labels = trans_format("log2", math_format(2^.x)),
               breaks = trans_breaks("log2", function(x) 2^(x - 1), n = 11)) +
  scale_y_log2(limits = c(0.01, NA),
               labels = trans_format("log2", math_format(2^.x)),
               breaks = trans_breaks("log2", function(x) 2^(x - 1), n = 11))
a + annotation_logticks(base = 2)

Answer 3

EDIT: A purely base approach:

df %>% 
  mutate_all(as.character)->new_df
res<-unlist(Map(function(x) eval(parse(text=x)),new_df$x))#replace with y for y
to_use<-unlist(lapply(res,as.expression))
split_text<-strsplit(gsub("\\^"," ",names(to_use))," ")
join_1<-as.numeric(sapply(split_text,"[[",1)) #tidyr::separate might help, less robust for numeric(I think)
join_2<-as.numeric(sapply(split_text,"[[",2))
to_use_1<-sapply(seq_along(join_1),function(x) parse(text=paste(join_1[x],"^",
                                                join_2[x])))

The above can be reduced to less step, I posted the stepwise approach I took. The result for only x, the same can be done for y:

new_df %>%   
ggplot()+
  geom_point(aes(x=x,y=y),size=4)+
 scale_x_discrete(breaks=df$x,labels=to_use_1)#replace with y and scale_y_discrete for y

Plot:

Original and erroneous answer:

I have deviated from standard tidyverse practice by using $, you can replace it with . and it might work although in this case it's not really important since the focus is on labels.:

    library(dplyr)
   df %>% 
          mutate(new_x=gsub("\\^"," ",x),
                 new_y=gsub("\\^"," ",y))->new_df
        new_df %>%   
        ggplot()+
          geom_point(aes(x=x,y=y),size=4)+
         scale_x_discrete(breaks=x,labels=new_df$new_x)+
          scale_y_discrete(breaks=y,labels=new_df$new_y)