How can I show a leading + sign in siunitx S column?

Question

I'm using siunitx's S columntype to align numbers in a table. The numbers are percentage values which should all have a preceding sign (some - and some +).

The numbers with a "-" are shown with a sign, the "+" sign vanishes as siunitx processes the numbers.

How can I keep the sign of the numbers including the "+" sign?

Answer 1

Pluses are retained is retain-explicit-plus is set

\documentclass{article}
\usepackage{siunitx}
\begin{document}
\begin{tabular}{S[retain-explicit-plus]}
  +1.23 \\
  -4.56 \\
   7.89 \\
\end{tabular}
\end{doument}

Answer 2

Okay, seems that I've found a solution:

I tried retain-explicit-plus as an option for \num but that doesn't do any good in tables.

What I did is fairly similar to this question:

Just omit the "+" sign for numbers that are positive (which gives them the "+" sign stated in S[explicit-sign=+]) and write a minus sign for negative numbers. This makes it work for mixed sign columns!