[Tex/LaTex] How to place thick vertical line in table

Question

I have a table like this at the moment:

Made up of the following LaTeX:

\begin{table} [htbp]
        \centering
        \begin{tabular}{p{2.50cm}|p{0.25cm}|p{0.25cm}|p{0.25cm}|p{0.25cm}}
            % \multirow{1}{*} {\textbf{Authors}} & & & & & & & & \textbf{Context and use of RSS} \\        &
            & \rotatebox{90}{Student 3} &
            \rotatebox{90}{Student 4} &
            \rotatebox{90}{Student 6} &
            \rotatebox{90}{Student 9} \\
            \thickhline
            Student 3 & & & & \\
            \hline
            Student 4 & \checkmark & & \\
            \hline
            Student 6 & \checkmark & \checkmark & \\
            \hline
            Student 9 & \checkmark & \checkmark & \checkmark & \\
            \thickhline
        \end{tabular}
        \caption{Averaging of correlations for RSS feed 140.}
        \label{tab:CorrelationAveraging}
    \end{table}

But would like to have the first vertical line as thick as either the first horizontal line or last horizontal line.

Can anyone advise how this can be done with the packages specified in the MWE below?

Instruction \thickhline is:

\newcommand{\thickhline}{%
    \noalign {\ifnum 0=`}\fi \hrule height 1.5pt
    \futurelet \reserved@a \@xhline
}

A full MWE is listed below:

\documentclass[a4paper,11pt]{article}

\usepackage{alltt}
\usepackage{anysize}
\usepackage{array}
\usepackage{booktabs}
\usepackage{caption}
\usepackage{changepage}
\usepackage{color}
\usepackage{enumerate}
\usepackage{etoolbox}
\usepackage{fancyhdr}
\usepackage{fixltx2e}
\usepackage[hang,flushmargin]{footmisc}
% \usepackage{graphics}
\usepackage{longtable}
\usepackage{ragged2e}
\usepackage[numbers,sort]{natbib}
%\usepackage{url}
\usepackage[normalem]{ulem}
\usepackage{subcaption}
\usepackage{float}
\usepackage{makecell}
\usepackage{rotating}
\usepackage{multirow}
\usepackage{amssymb}
\usepackage{amsmath}
\usepackage{amsfonts}

\marginsize{2.54cm}{2.54cm}{2.54cm}{2.54cm}

% Tables.
\newcolumntype{C}[1]{>{\centering\arraybackslash}p{#1}}
\newcolumntype{R}[1]{>{\RaggedLeft\arraybackslash}p{#1}}
\setlength\heavyrulewidth{0.25ex}
\setlength\lightrulewidth{0.25ex}

\renewcommand\theadfont{\bfseries}
\settowidth\rotheadsize{\theadfont pair}

\makeatletter
\newcommand{\thickhline}{%
   \noalign {\ifnum 0=`}\fi \hrule height 1.50pt
   \futurelet \reserved@a \@xhline
}
\newcolumntype{"}{@{\hskip\tabcolsep\vrule width 1pt\hskip\tabcolsep}}
\makeatother

\begin{document}

\title{Title}

\author{Author}

\maketitle

    \begin{table} [htbp]
    \centering
    \begin{tabular}{p{1.65cm}|p{0.25cm}|p{0.25cm}|p{0.25cm}|p{0.25cm}}
        % \multirow{1}{*} {\textbf{Authors}} & & & & & & & & \textbf{Context and use of RSS} \\        &
        & \rotatebox{90}{Student 3} &
        \rotatebox{90}{Student 4} &
        \rotatebox{90}{Student 6} &
        \rotatebox{90}{Student 9} \\
        \thickhline
        Student 3 & & & & \\
        \hline
        Student 4 & \checkmark & & \\
        \hline
        Student 6 & \checkmark & \checkmark & \\
        \hline
        Student 9 & \checkmark & \checkmark & \checkmark & \\
        \thickhline
    \end{tabular}
    \caption{Example of averaging of correlations for a sentiment for RSS feed 140.}
    \label{tab:CorrelationAveraging}
    \end{table}

\end{document}

Answer 1

Don't reinvent the wheel: it all exists with the \hlineB, clineB commands and the V column separator, defined in the boldline package, from the shipunov bundle. They all accept a number as an argument, which is a factor in front of \arrayrulewidth. Rules with 1.5pt thickness are approximately 4\arrayrulewidth:

\documentclass{article}
\usepackage[utf8]{inputenc} 
\usepackage{amssymb}
\usepackage{array, boldline, rotating}

\newcommand{\thickhline}{\hlineB{4}}

\begin{document}

\begin{table} [htbp]
    \centering
    \begin{tabular}{p{2.50cm}V{4}*{4}{p{0.25cm}|}}
        % \multirow{1}{*} {\textbf{Authors}} & & & & & & & & \textbf{Context and use of RSS} \\ &
        & \rotatebox{90}{Student 3} &
        \rotatebox{90}{Student 4} &
        \rotatebox{90}{Student 6} &
        \rotatebox{90}{Student 9} \\
        \thickhline
        Student 3 & & & & \\
        \hline
        Student 4 & \checkmark & & & \\
        \hline
        Student 6 & \checkmark & \checkmark & & \\
        \hline
        Student 9 & \checkmark & \checkmark & \checkmark & \\
        \thickhline
    \end{tabular}
    \caption{Averaging of correlations for RSS feed 140.}
    \label{tab:CorrelationAveraging}
\end{table}

\end{document}