Centering a value on a row with multicolumns

Question

I have the following table with 5 rows with a first column of text and 4 columns of data :

\newenvironment{mytable}[1][h!]{\begin{table}[#1]\centering\small}{\end{table}}
\begin{mytable}
\begin{center}
\begingroup
\setlength{\tabcolsep}{3pt} % Default value: 6pt
\renewcommand{\arraystretch}{1} % Default value: 1
\begin{tabular}{|c|c|c|c|c|}
\hline
\addstackgap{Redshift central bin} & 1.0 & 1.2 & 1.4 & 1.65 \ \hline
\addstackgap{$\mathrm{d}N / \mathrm{d}\Omega\mathrm{d}z\left[\mathrm{deg}^{-2}\right]$} & 1815.0 & 1701.5 & 1410.0 & 940.97 \ \hline
\addstackgap{$\Delta z$ : width of bin} & 0.2 & 0.2 & 0.2 & 0.3 \ \hline
\addstackgap{$\rho_{gal}$,(gal.arcmin$^{-2}$}) & 0.1008 & 0.0945 & 0.0783 & 0.0784 \ \hline
\addstackgap{$\rho_{gal,tot}$,(gal.arcmin$^{-2}$)} & 
\multicolumn{1}{c}{}  0.3521 &
\multicolumn{1}{c}{} &

\multicolumn{1}{c}{} & \
\hline
\end{tabular}
\endgroup
\end{center}
\caption{Spectroscopic specifications from \citetalias{IST:paper1} with 4 bins}
\label{density1}
\end{mytable}\

Here is the rendering :

I would like to keep the same format excepted the fact that I should center the value 0.3521 on the last row, between the first and fourth column.

Could anyone see how to perform this centering ?

Answer 1

For information, here is the way to construct that table with nicematrix.

\documentclass{article}
\usepackage{nicematrix}
\begin{document}
\begin{table}
\centering
\renewcommand{\arraystretch}{1.4}
\begin{NiceTabular}{ccccc}[hvlines]
Redshift central bin & 1.0 & 1.2 & 1.4 & 1.65 \ 
$\mathrm{d}N / \mathrm{d}\Omega\mathrm{d}z\left[\mathrm{deg}^{-2}\right]$ & 1815.0 & 1701.5 & 1410.0 & 940.97 \ 
$\Delta z$ : width of bin & 0.2 & 0.2 & 0.2 & 0.3 \ 
$\rho_{gal}$,(gal.arcmin$^{-2}$) & 0.1008 & 0.0945 & 0.0783 & 0.0784 \ 
$\rho_{gal,tot}$,(gal.arcmin$^{-2}$) & \Block{1-4}{0.3521}
\end{NiceTabular}
\caption{Spectroscopic specifications from XXXXXXX with 4 bins}\label{density1}
\end{table}
\end{document}

Answer 2

I would like to show you a solution with tabularray:

\documentclass{article}
\usepackage{tabularray}
\newenvironment{mytable}[1][h]{\begin{table}[#1]\centering\small}{\end{table}}
\begin{document}
\begin{mytable}
\begin{tblr}{
    colspec={*5{c}},
    hlines,vlines,
    rows={rowsep+=2pt},
    colsep=3pt
    }
Redshift central bin & 1.0 & 1.2 & 1.4 & 1.65 \ 
$\mathrm{d}N / \mathrm{d}\Omega\mathrm{d}z\left[\mathrm{deg}^{-2}\right]$ & 1815.0 & 1701.5 & 1410.0 & 940.97 \ 
$\Delta z$ : width of bin & 0.2 & 0.2 & 0.2 & 0.3 \ 
$\rho_{gal}$,(gal.arcmin$^{-2}$) & 0.1008 & 0.0945 & 0.0783 & 0.0784 \ 
$\rho_{gal,tot}$,(gal.arcmin$^{-2}$) & 
\SetCell[c=4]{c} 0.3521 &&&\
\end{tblr}
\caption{Spectroscopic specifications from XXXXXXX with 4 bins}\label{density1}
\end{mytable}
\end{document}

However, with your MWE, as frabjous suggested, use \multicolumn{4}{c|}{0.3521}:

\documentclass{article}
\usepackage{stackengine}
\newenvironment{mytable}[1][h]{\begin{table}[#1]\centering\small}{\end{table}}
\begin{document}
\begin{mytable}
%\begin{center}<--- no, you're already using \centering and see https://tex.stackexchange.com/questions/23650/when-should-we-use-begincenter-instead-of-centering
%\begingroup<--- Why this? you're already in a group
\setlength{\tabcolsep}{3pt} % Default value: 6pt
\renewcommand{\arraystretch}{1} % Default value: 1
\begin{tabular}{|c|c|c|c|c|}
\hline
\addstackgap{Redshift central bin} & 1.0 & 1.2 & 1.4 & 1.65 \ \hline
\addstackgap{$\mathrm{d}N / \mathrm{d}\Omega\mathrm{d}z\left[\mathrm{deg}^{-2}\right]$} & 1815.0 & 1701.5 & 1410.0 & 940.97 \ \hline
\addstackgap{$\Delta z$ : width of bin} & 0.2 & 0.2 & 0.2 & 0.3 \ \hline
\addstackgap{$\rho_{gal}$,(gal.arcmin$^{-2}$)} & 0.1008 & 0.0945 & 0.0783 & 0.0784 \ \hline
\addstackgap{$\rho_{gal,tot}$,(gal.arcmin$^{-2}$)} & \multicolumn{4}{c|}{0.3521} \
\hline
\end{tabular}
%\endgroup
%\end{center}
\caption{Spectroscopic specifications from XXXXXXX with 4 bins}\label{density1}
\end{mytable}%\<--- don't use \ outside tables
\end{document}