Bob Bob - 1 year ago 142
R Question

In R, why is there awkward output in the legend when I am using paste() instead of c() in addition to pretty10exp()?

I'm trying to make the legend of this plot pretty, so I need there the be an actual superscript, which is why I am using the pretty10exp() function from the sfsmisc library. It works when I use the c() function.

However, I am also trying to keep the string and the scientific notation number on the same line. The legend() is broken into two lines, which I think is due to c(). I thought I could use paste(), but for some reason the output is now incorrect.

pVal <- 4
legend("topright", legend = c("P value:", sfsmisc::pretty10exp(pVal)), cex = 1.5)

legend("topright", legend = paste("P value:", sfsmisc::pretty10exp(pVal)), cex = 1.5)

pVal being an arbitrary number represented in scientific notation. The second line results in output like this:
"P value: (significand) %*% 10^-4"
. The first line also doesn't give me what I want. How can I fix this problem?

Answer Source

pretty10exp returns an expression which allows it to use the ?plotmath features for making nice looking numbers. When working with expressions, you can't just paste values in like strings. You need to manipulate them with a special set of functions. One such function is substitute. You can do

pVal <- 4
legend("topright", cex = 1.5, 
    legend = substitute("P value: "*x, list(x=sfsmisc::pretty10exp(pVal)[[1]])) )

We use substitute() to take the value contained in the expression from pretty10exp and prefix it with the label you want. (We use * to concatenate rather than paste() since plotmath allows it)

enter image description here

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