Centered text in Tikz nodes with linebreaks does not work properly

Question

I want to place a two lines text inside each node in a grid and want them to be centered. Now I am aware of this among other threads. E.g. the most natural solution would be to use align=center in combination with linebreaks \\ inside the node text brackets.

Picture and MWE below. As you can see, the letters are not centered, while the numbering is. I tried:

• align + \\
• text width, alone and in combination with the above
• tabular environment inside the node text brackets
• removing the \scriptsize parameter I use As you can see, I use nested for loops to create a grid that counts up in a serpentine formation. Certain groups of indices (predefined externally) receiver certain letters, I achieve this with the defined command \mylabel. Got the idea for this from my question earlier. However, I just cant get the letters to align centered with the numbers in the line below.

\documentclass{standalone}
\usepackage{tikz}
%=================================
\def\groupC{{2,11,13,22,24,33,35,44,46,55,57,66,68,77,79,88}}
\def\groupA{{3,4,5,6,7,8,9,10,14,15,16,17,18,19,20,21,25,26,27,28,29,30,31,32,36,37,38,39,40,41,42,43,47,48,49,50,51,52,53,54,58,59,60,61,62,63,64,65,69,70,71,72,73,74,75,76,80,81,82,83,84,85,86,87}}
\def\groupH{{12,23,34,45,56,67,78}}
\def\groupO{{89}}
\newcommand{\mylabel}[1]
{%
  \pgfmathtruncatemacro{\num}{#1}
  \foreach\c in {0,...,15}
  {%
    \pgfmathtruncatemacro{\temp}{\groupC[\c]}%
    \ifnum \num = \temp \scriptsize C\fi
  }
  \foreach\a in {0,...,63}
  {%
    \pgfmathtruncatemacro{\temp}{\groupA[\a]}%
    \ifnum \num = \temp \scriptsize A\fi
  }

  \foreach\h in {0,...,6}
  {%
    \pgfmathtruncatemacro{\temp}{\groupH[\h]}%
    \ifnum \num = \temp \scriptsize H\fi
  }
  \ifnum \num = 89 \scriptsize O\fi 
}
\begin{document}
\begin{tikzpicture}[node distance=1cm]
\foreach \i in {0,...,7}
  \foreach \j in {0,...,10}
    {\pgfmathtruncatemacro{\label}{11\i+\j+2}
    {\pgfmathsetmacro{\x}{1\j(-1)^(\i) + 5(-1)^(\i+1)}
    \node (e\label) [rectangle, draw=black, minimum width=1cm, align=center] at (\x,-1*\i) {
    \mylabel{\label}\[-5pt]
    \scriptsize(\label)
    };
    }}
\end{tikzpicture}
\end{document}

Answer 1

The align is good, but there are a couple of unwanted spaces that you can't see. Try to enclose the \mylabel command in a \fbox and you'll see these spaces:

\fbox{\mylabel{\label}}\\[-5pt]

You can do the following to prevent the not needed spaces:

\documentclass{standalone}
\usepackage{tikz}
%=================================
\def\groupC{{2,11,13,22,24,33,35,44,46,55,57,66,68,77,79,88}}
\def\groupA{{3,4,5,6,7,8,9,10,14,15,16,17,18,19,20,21,25,26,27,28,29,30,31,32,36,37,38,39,40,41,42,43,47,48,49,50,51,52,53,54,58,59,60,61,62,63,64,65,69,70,71,72,73,74,75,76,80,81,82,83,84,85,86,87}}
\def\groupH{{12,23,34,45,56,67,78}}
\def\groupO{{89}}
\newcommand{\mylabel}[1]
{%
  \pgfmathtruncatemacro{\num}{#1}% <-- to prevent unwanted spaces
  \scriptsize% you can put this here instead of inside each loop (unrelated)
  \foreach\c in {0,...,15}
  {%
    \pgfmathtruncatemacro{\temp}{\groupC[\c]}%
    \ifnum \num = \temp C\fi
  }% <-- to prevent unwanted spaces
  \foreach\a in {0,...,63}
  {%
    \pgfmathtruncatemacro{\temp}{\groupA[\a]}%
    \ifnum \num = \temp A\fi
  }% <-- to prevent unwanted spaces
  \foreach\h in {0,...,6}
  {%
    \pgfmathtruncatemacro{\temp}{\groupH[\h]}%
    \ifnum \num = \temp H\fi
  }% <-- to prevent unwanted spaces
  \ifnum \num = 89  O\fi
}
\begin{document}
\begin{tikzpicture}[node distance=1cm]
\foreach \i in {0,...,7}
  \foreach \j in {0,...,10}
    {\pgfmathtruncatemacro{\label}{11\i+\j+2}
    {\pgfmathsetmacro{\x}{1\j(-1)^(\i) + 5(-1)^(\i+1)}
    \node (e\label) [rectangle, draw=black, minimum width=1cm, align=center] at (\x,-1*\i) {
    \mylabel{\label}\[-5pt]
    \scriptsize(\label)
    };
    }}
\end{tikzpicture}
\end{document}

Edit: for a better compiling time if the groups are not needed in other part of the picture, it would be faster to change the macro in this way (and to remove the groups definitions, not needed now):

\newcommand{\mylabel}[1]
{%
  \pgfmathtruncatemacro{\num}{#1}% <-- to prevent unwanted spaces
  \scriptsize% you can put this here instead of inside each loop
  \foreach\c in { 2,11,13,22,24,33,35,44,46,55,57,66,68,77,79,88} % GROUP C
    {\ifnum \num = \c C\fi}% <-- to prevent unwanted spaces
  \foreach\a in { 3, 4, 5, 6, 7, 8, 9,10,14,15,16,17,18,19,20,21, % GROUP A
                 25,26,27,28,29,30,31,32,36,37,38,39,40,41,42,43,
                 47,48,49,50,51,52,53,54,58,59,60,61,62,63,64,65,
                 69,70,71,72,73,74,75,76,80,81,82,83,84,85,86,87}
    {\ifnum \num = \a A\fi}% <-- to prevent unwanted spaces
  \foreach\h in {12,23,34,45,56,67,78}                            % GROUP H
    {\ifnum \num = \h H\fi}% <-- to prevent unwanted spaces
  \ifnum \num = 89  O\fi                                          % GROUP O
}

Note: Perhaps I should have pointed all this in my previous answer.