Question

How can one concisely change a numeric R variable (keeping it numeric) so that, e.g.,
“-0.34” becomes simply “-.34”?

Answer 1

Only when you output a numeric value do you have to choose a concrete representation (i.e., how the number should be formatted). You cannot change a numeric variable from “-0.34” to “-.34”; both are representations for the same number.

However, when you output an expression e, you can choose how it should be formatted. I don’t know of any build-in way to leave off the leading “0”, but you could always just remove it manually:

> sub("^(-?)0.", "\\1.", sprintf("%.2f", -0.34))
[1] "-.34"

You can define a function for convenience, e.g.,

numformat <- function(val) { sub("^(-?)0.", "\\1.", sprintf("%.2f", val)) }