%\begin{table}[htbp]
\small
\centering
\caption{Add caption}
\begin{tabular}{|l|p{4.855em}|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|}
\toprule
\multicolumn{2}{|l|}{} & \multicolumn{1}{p{4.215em}|}{NIM (\%)} & \multicolumn{1}{p{4.215em}|}{GDP (\%)} & \multicolumn{1}{p{4.215em}|}{ROE} & \multicolumn{1}{p{4.215em}|}{ROA} & \multicolumn{1}{p{4.215em}|}{INFLTN} & \multicolumn{1}{p{4.215em}|}{FDI} & \multicolumn{1}{p{4.215em}|}{BCBD (\%)} & \multicolumn{1}{p{4.215em}|}{DBACBA (\%)} & \multicolumn{1}{p{4.215em}|}{CBAGDP (\%)} & \multicolumn{1}{p{4.215em}|}{DBAGDP (\%)} & \multicolumn{1}{p{4.215em}|}{FDGDP (\%)} & \multicolumn{1}{p{4.215em}|}{LISTCO\_PC} & \multicolumn{1}{p{4.215em}|}{LL\_USD} & \multicolumn{1}{p{4.215em}|}{XREGME} & \multicolumn{1}{p{4.215em}|}{XREGCON} & \multicolumn{1}{p{4.215em}|}{OVERHEAD (\%)} & \multicolumn{1}{p{4.215em}|}{LLGDP (\%)} & \multicolumn{1}{p{4.215em}|}{STMKCAP (\%)} & \multicolumn{1}{p{4.215em}|}{STVALT\_D (\%)} & \multicolumn{1}{p{4.215em}|}{STTURN\_R (\%)} & \multicolumn{1}{p{4.215em}|}{NRBLOAN (\%)} \\
\midrule
\multicolumn{1}{|l|}{\multirow{21}[41]{*}{Pearson Correlation}} & NIM (\%) & 1.000 & .068 & .466 & .556 & .325 & -.030 & -.322 & -.418 & .304 & -.280 & -.329 & -.312 & -.081 & -.329 & .470 & .593 & -.386 & -.182 & -.114 & .102 & .016 \\
\cmidrule{2-2} & GDP (\%) & .068 & 1.000 & -.015 & .111 & .044 & -.089 & -.079 & .013 & -.036 & .006 & -.031 & .002 & .103 & -.240 & .329 & .143 & -.045 & -.454 & -.461 & .037 & -.234 \\
\cmidrule{2-2} & ROE & .466 & -.015 & 1.000 & .810 & .097 & .234 & -.162 & .139 & -.095 & -.067 & .058 & .064 & -.159 & .221 & -.068 & -.164 & .018 & .070 & .074 & -.026 & .087 \\
\cmidrule{2-2} & ROA & .556 & .111 & .810 & 1.000 & .246 & -.034 & -.153 & .034 & -.054 & -.048 & -.018 & -.058 & -.072 & .018 & .222 & -.014 & -.059 & -.044 & -.041 & -.053 & -.010 \\
\cmidrule{2-2} & INFLTN & .325 & .044 & .097 & .246 & 1.000 & -.231 & -.146 & -.335 & .321 & -.065 & -.142 & -.115 & -.012 & -.292 & .308 & .048 & -.134 & -.081 & -.051 & .091 & -.072 \\
\cmidrule{2-2} & FDI & -.030 & -.089 & .234 & -.034 & -.231 & 1.000 & -.172 & -.049 & .131 & -.165 & .066 & .105 & -.169 & .315 & -.294 & .010 & -.021 & .271 & .259 & -.029 & -.069 \\
\cmidrule{2-2} & BCBD (\%) & -.322 & -.079 & -.162 & -.153 & -.146 & -.172 & 1.000 & .375 & -.334 & .394 & .179 & .208 & .158 & .206 & -.522 & -.262 & .254 & .079 & .071 & .042 & .391 \\
\cmidrule{2-2} & DBACBA (\%) & -.418 & .013 & .139 & .034 & -.335 & -.049 & .375 & 1.000 & -.884 & .364 & .453 & .298 & .318 & .268 & -.248 & -.569 & .440 & .105 & .083 & .150 & -.139 \\
\cmidrule{2-2} & CBAGDP (\%) & .304 & -.036 & -.095 & -.054 & .321 & .131 & -.334 & -.884 & 1.000 & -.203 & -.266 & -.174 & -.238 & -.295 & .221 & .513 & -.269 & -.086 & -.069 & -.106 & .075 \\
\cmidrule{2-2} & DBAGDP (\%) & -.280 & .006 & -.067 & -.048 & -.065 & -.165 & .394 & .364 & -.203 & 1.000 & .900 & .794 & .045 & -.218 & -.247 & -.393 & .929 & .087 & .030 & -.026 & .155 \\
\cmidrule{2-2} & FDGDP (\%) & -.329 & -.031 & .058 & -.018 & -.142 & .066 & .179 & .453 & -.266 & .900 & 1.000 & .819 & -.039 & -.036 & -.270 & -.463 & .974 & .134 & .065 & -.022 & .040 \\
\cmidrule{2-2} & LISTCO\_PC & -.312 & .002 & .064 & -.058 & -.115 & .105 & .208 & .298 & -.174 & .794 & .819 & 1.000 & -.074 & .105 & -.451 & -.419 & .806 & .121 & .064 & .015 & .042 \\
\cmidrule{2-2} & LL\_USD & -.081 & .103 & -.159 & -.072 & -.012 & -.169 & .158 & .318 & -.238 & .045 & -.039 & -.074 & 1.000 & -.301 & .204 & -.108 & -.086 & -.034 & -.016 & .060 & -.303 \\
\cmidrule{2-2} & XREGME & -.329 & -.240 & .221 & .018 & -.292 & .315 & .206 & .268 & -.295 & -.218 & -.036 & .105 & -.301 & 1.000 & -.706 & -.255 & -.018 & .177 & .151 & .034 & .220 \\
\cmidrule{2-2} & XREGCON & .470 & .329 & -.068 & .222 & .308 & -.294 & -.522 & -.248 & .221 & -.247 & -.270 & -.451 & .204 & -.706 & 1.000 & .407 & -.342 & -.345 & -.308 & .013 & -.489 \\
\cmidrule{2-2} & OVERHEAD (\%) & .593 & .143 & -.164 & -.014 & .048 & .010 & -.262 & -.569 & .513 & -.393 & -.463 & -.419 & -.108 & -.255 & .407 & 1.000 & -.495 & -.311 & -.254 & .125 & -.060 \\
\cmidrule{2-2} & LLGDP (\%) & -.386 & -.045 & .018 & -.059 & -.134 & -.021 & .254 & .440 & -.269 & .929 & .974 & .806 & -.086 & -.018 & -.342 & -.495 & 1.000 & .110 & .035 & -.052 & .145 \\
\cmidrule{2-2} & STMKCAP (\%) & -.182 & -.454 & .070 & -.044 & -.081 & .271 & .079 & .105 & -.086 & .087 & .134 & .121 & -.034 & .177 & -.345 & -.311 & .110 & 1.000 & .988 & -.023 & .162 \\
\cmidrule{2-2} & STVALT\_D (\%) & -.114 & -.461 & .074 & -.041 & -.051 & .259 & .071 & .083 & -.069 & .030 & .065 & .064 & -.016 & .151 & -.308 & -.254 & .035 & .988 & 1.000 & .083 & .168 \\
\cmidrule{2-2} & STTURN\_R (\%) & .102 & .037 & -.026 & -.053 & .091 & -.029 & .042 & .150 & -.106 & -.026 & -.022 & .015 & .060 & .034 & .013 & .125 & -.052 & -.023 & .083 & 1.000 & .051 \\
\cmidrule{2-2} & NRBLOAN (\%) & .016 & -.234 & .087 & -.010 & -.072 & -.069 & .391 & -.139 & .075 & .155 & .040 & .042 & -.303 & .220 & -.489 & -.060 & .145 & .162 & .168 & .051 & 1.000 \\
\end{tabular}%
\label{tab:addlabel}%
%\end{table}%
答案1
让 21x21 的相关表看起来“不错”始终是一项严峻的艺术挑战。（另外：您有什么理由相信您的读者会关心完整的相关表吗？如果您只报告真正重要的 2 或 3 个相关性，他们会不会感觉一样好，甚至更好？）
一些建议：
为了节省大量稀缺的水平空间，请省略整个第一列，并将字符串“Pearson Correlation”放置在 的参数中
\caption。加载
sidewaystable包并将整个表封装在sidewaystable环境中。我相信你能猜出sidewaystable环境的作用。大大简化标题单元格。不要说明变量名称，只需将列编号为 (1)、(2) 等。没有足够的空间再次列出变量名称。毕竟，您已经在第一列中列出了变量名称。
删除所有 23 条 [!] 垂直线（您会惊讶于 23 条线会占用多少空间）和 23 条水平线中的 20 条。加载包
booktabs并使用\toprule、\midrule和\bottomrule绘制剩余的 3 条水平线。可选：\addlinespace在每 5 行后插入指令。使用
tabular*环境并将其整体宽度设置为\textwidth。对数据列使用数学模式，以确保
-符号排版为数学减号符号，而不是文本模式的“破折号”符号即使进行了所有这些调整，您仍然需要将字体大小切换为
\footnotesize或 甚至\scriptsize。
\documentclass{article}
\usepackage[a4paper,margin=2.5cm]{geometry} % set page size parameters appropriately
\usepackage{booktabs,rotating,array,caption}
\newcolumntype{R}{>{$}r<{$}} % right-aligned, math mode
\begin{document}
\begin{sidewaystable}
\captionsetup{skip=0.5\baselineskip,font=footnotesize}
\caption{Pearson Correlations} \label{tab:addlabel}
\footnotesize % or even "\scriptsize", if necessary
\setlength\extrarowheight{2pt} % optional; for a more open "look"
\setlength\tabcolsep{0pt} % make LaTeX figure out max. intercol. whitespace
\begin{tabular*}{\textwidth}{@{\extracolsep{\fill}} l *{21}{R} }
\toprule
& (1) & (2) & (3) & (4) & (5) & (6) & (7) & (8) & (9) & (10)
& (11) & (12) & (13) & (14) & (15) & (16) & (17) & (18) & (19) & (20) & (21) \\
\midrule
(1) NIM (\%) & 1.000 & .068 & .466 & .556 & .325 & -.030 & -.322 & -.418 & .304 & -.280 & -.329 & -.312 & -.081 & -.329 & .470 & .593 & -.386 & -.182 & -.114 & .102 & .016 \\
(2) GDP (\%) & .068 & 1.000 & -.015 & .111 & .044 & -.089 & -.079 & .013 & -.036 & .006 & -.031 & .002 & .103 & -.240 & .329 & .143 & -.045 & -.454 & -.461 & .037 & -.234 \\
(3) ROE & .466 & -.015 & 1.000 & .810 & .097 & .234 & -.162 & .139 & -.095 & -.067 & .058 & .064 & -.159 & .221 & -.068 & -.164 & .018 & .070 & .074 & -.026 & .087 \\
(4) ROA & .556 & .111 & .810 & 1.000 & .246 & -.034 & -.153 & .034 & -.054 & -.048 & -.018 & -.058 & -.072 & .018 & .222 & -.014 & -.059 & -.044 & -.041 & -.053 & -.010 \\
(5) INFLTN & .325 & .044 & .097 & .246 & 1.000 & -.231 & -.146 & -.335 & .321 & -.065 & -.142 & -.115 & -.012 & -.292 & .308 & .048 & -.134 & -.081 & -.051 & .091 & -.072 \\
\addlinespace
(6) FDI & -.030 & -.089 & .234 & -.034 & -.231 & 1.000 & -.172 & -.049 & .131 & -.165 & .066 & .105 & -.169 & .315 & -.294 & .010 & -.021 & .271 & .259 & -.029 & -.069 \\
(7) BCBD (\%) & -.322 & -.079 & -.162 & -.153 & -.146 & -.172 & 1.000 & .375 & -.334 & .394 & .179 & .208 & .158 & .206 & -.522 & -.262 & .254 & .079 & .071 & .042 & .391 \\
(8) DBACBA (\%) & -.418 & .013 & .139 & .034 & -.335 & -.049 & .375 & 1.000 & -.884 & .364 & .453 & .298 & .318 & .268 & -.248 & -.569 & .440 & .105 & .083 & .150 & -.139 \\
(9) CBAGDP (\%) & .304 & -.036 & -.095 & -.054 & .321 & .131 & -.334 & -.884 & 1.000 & -.203 & -.266 & -.174 & -.238 & -.295 & .221 & .513 & -.269 & -.086 & -.069 & -.106 & .075 \\
(10) DBAGDP (\%) & -.280 & .006 & -.067 & -.048 & -.065 & -.165 & .394 & .364 & -.203 & 1.000 & .900 & .794 & .045 & -.218 & -.247 & -.393 & .929 & .087 & .030 & -.026 & .155 \\
\addlinespace
(11) FDGDP (\%) & -.329 & -.031 & .058 & -.018 & -.142 & .066 & .179 & .453 & -.266 & .900 & 1.000 & .819 & -.039 & -.036 & -.270 & -.463 & .974 & .134 & .065 & -.022 & .040 \\
(12) LISTCO\_PC & -.312 & .002 & .064 & -.058 & -.115 & .105 & .208 & .298 & -.174 & .794 & .819 & 1.000 & -.074 & .105 & -.451 & -.419 & .806 & .121 & .064 & .015 & .042 \\
(13) LL\_USD & -.081 & .103 & -.159 & -.072 & -.012 & -.169 & .158 & .318 & -.238 & .045 & -.039 & -.074 & 1.000 & -.301 & .204 & -.108 & -.086 & -.034 & -.016 & .060 & -.303 \\
(14) XREGME & -.329 & -.240 & .221 & .018 & -.292 & .315 & .206 & .268 & -.295 & -.218 & -.036 & .105 & -.301 & 1.000 & -.706 & -.255 & -.018 & .177 & .151 & .034 & .220 \\
(15) XREGCON & .470 & .329 & -.068 & .222 & .308 & -.294 & -.522 & -.248 & .221 & -.247 & -.270 & -.451 & .204 & -.706 & 1.000 & .407 & -.342 & -.345 & -.308 & .013 & -.489 \\
\addlinespace
(16) OVERHEAD (\%) & .593 & .143 & -.164 & -.014 & .048 & .010 & -.262 & -.569 & .513 & -.393 & -.463 & -.419 & -.108 & -.255 & .407 & 1.000 & -.495 & -.311 & -.254 & .125 & -.060 \\
(17) LLGDP (\%) & -.386 & -.045 & .018 & -.059 & -.134 & -.021 & .254 & .440 & -.269 & .929 & .974 & .806 & -.086 & -.018 & -.342 & -.495 & 1.000 & .110 & .035 & -.052 & .145 \\
(18) STMKCAP (\%) & -.182 & -.454 & .070 & -.044 & -.081 & .271 & .079 & .105 & -.086 & .087 & .134 & .121 & -.034 & .177 & -.345 & -.311 & .110 & 1.000 & .988 & -.023 & .162 \\
(19) STVALT\_D (\%) & -.114 & -.461 & .074 & -.041 & -.051 & .259 & .071 & .083 & -.069 & .030 & .065 & .064 & -.016 & .151 & -.308 & -.254 & .035 & .988 & 1.000 & .083 & .168 \\
(20) STTURN\_R (\%) & .102 & .037 & -.026 & -.053 & .091 & -.029 & .042 & .150 & -.106 & -.026 & -.022 & .015 & .060 & .034 & .013 & .125 & -.052 & -.023 & .083 & 1.000 & .051 \\
(21) NRBLOAN (\%) & .016 & -.234 & .087 & -.010 & -.072 & -.069 & .391 & -.139 & .075 & .155 & .040 & .042 & -.303 & .220 & -.489 & -.060 & .145 & .162 & .168 & .051 & 1.000 \\
\bottomrule
\end{tabular*}
\end{sidewaystable}
\end{document}