How to Realign a Horizontal Stack with the Above Item

Question

Consider the MWE

\documentclass{article}
\textheight 8.25in \textwidth 4.75in
\usepackage{scalefnt}
\usepackage{amsmath,amssymb}

%\blacksquare\hspace*{.7em}
\usepackage{stackengine,xcolor,lipsum}
\let\svitem\item
\newcommand\difbox[1]{\stackengine{0pt}{\color{white}\rule{5ex}{1.15ex}}{%
    $\iftrue\makeballs#1\fi$}{O}{c}{F}{F}{L} }
\def\makeballs#1#2\fi{\fi\ifx R#1\textcolor{red}{\blacksquare}\else
  \ifx B#1\textcolor{blue!35}{\blacksquare}\fi\fi%
  \ifx\relax#2\relax\else\makeballs#2\fi}
\newenvironment{benumerate}
{\renewcommand\item[1][1]{\def\difficulty{##1}\svitem}%
  \def\labelenumi{\smash{\stackunder[5pt]{\color{blue!65!black}%
  \bfseries\sffamily\theenumi}{\expandafter\difbox\expandafter{\difficulty}}}}%
  \enumerate}{\endenumerate}

\begin{document}
\large
\begin{benumerate}
\setcounter{enumi}{0}
\item[RBRRBR] \lipsum[11]
\item[RRR] \lipsum[39]
\item[BRRRB] \lipsum[13]
\end{benumerate}
\end{document}

with output

I would like to widen the gap between the colored squares; but when I replace both instances of \blacksquare with \blacksquare\hspace*{.7em}---I get the extra spacing I want, but relative to the above enumeration, the new horizontal stack appears to be non-aligned; i.e., not lying centered beneath the above number, as follows:

Now, the alignment in the first output is not perfect, but reasonably accurate. However, the alignment in the second output is clearly not centered beneath the corresponding number.

QUESTION: How may I increase the gap between the colored boxes of the original output so that the horizontal stack of colored squares lies reasonably centered below the upper number?

Thank you.

Answer 1

You can use \unskip at the end to remove the trailing space that is causing the offset:

\documentclass{article}
\textheight 8.25in \textwidth 4.75in
\usepackage{scalefnt}
\usepackage{amsmath,amssymb}

\usepackage{stackengine,xcolor,lipsum}
\let\svitem\item
\newcommand\difbox[1]{\stackengine{0pt}{\color{white}\rule{5ex}{1.15ex}}{\makeballs{#1}}{O}{c}{F}{F}{L}}

\newcommand\makeballs[1]{$\iftrue\makeballsA#1\fi \unskip$}
\def\makeballsA#1#2\fi{\fi
  \ifx R#1\textcolor{red}{\blacksquare}\else
  \ifx B#1\textcolor{blue!35}{\blacksquare}\fi\fi \hspace{.7em}%
  \ifx\relax#2\relax \else\makeballsA#2\fi}
  
\newenvironment{benumerate}
{\renewcommand\item[1][1]{\def\difficulty{##1}\svitem}%
  \def\labelenumi{\smash{\stackunder[5pt]{\color{blue!65!black}%
  \bfseries\sffamily\theenumi}{\expandafter\difbox\expandafter{\difficulty}}}}%
  \enumerate}{\endenumerate}

\begin{document}
\large
\begin{benumerate}
\setcounter{enumi}{0}
\item[RBRRBR] \lipsum[11]
\item[RRR] \lipsum[39]
\item[BRRRB] \lipsum[13]
\end{benumerate}
\end{document}

Here I abstracted away \makeballs to a separate macro so it may be reused elsewhere without having to pay attention to the actual working details.

Also, \hspace (unstarred) or \hskip must be used here since \hspace* adds intervening boxes.

---

Addendum: another way is to add the space only if there is a next iteration.

\newcommand\makeballs[1]{$\iftrue\makeballsA#1\fi$}
\def\makeballsA#1#2\fi{\fi
  \ifx R#1\textcolor{red}{\blacksquare}\else
  \ifx B#1\textcolor{blue!35}{\blacksquare}\fi\fi
  \ifx\relax#2\relax \else\hspace{.7em}\makeballsA#2\fi}