In the solution provided here by egreg, how to go about splitting the data into three columns if the data is even larger like this:
Here is his code:
\documentclass[a4paper]{book}
\usepackage{booktabs}
\usepackage{amsmath}
\usepackage{siunitx}
\usepackage{xparse}
\usepackage{filecontents}
\ExplSyntaxOn
\ior_new:N \g_joe_file_stream
\tl_new:N \l__joe_file_body_tl
\int_new:N \l__joe_file_rows_int
\NewDocumentCommand{\readfile}{smm}
{% * = keep header, #2 = file name, #3 = symbolic name
\seq_clear_new:c { l_joe_file_#3_seq }
\ior_open:Nn \g_joe_file_stream { #2 }
\ior_map_inline:Nn \g_joe_file_stream
{
\seq_put_right:cn { l_joe_file_#3_seq } { ##1 }
}
\IfBooleanF{#1}{ \seq_pop_left:cN { l_joe_file_#3_seq } \l_tmpa_tl }
}
\NewDocumentCommand{\processdata}{mmmm}
{% #1 = name in, #2 = name out, #3 = code in, #4 = code out
\seq_clear_new:c { l_joe_file_#2_seq } % the output sequence
\cs_set:Npn \__joe_file_process:w #3 { #4 }
\seq_set_map:ccn { l_joe_file_#2_seq } { l_joe_file_#1_seq } { \__joe_file_process:w ##1 }
}
\cs_generate_variant:Nn \seq_set_map:NNn { cc }
\NewDocumentCommand{\maketable}{mmmm}
{% #1 = cols, #2 = table preamble, #3 = headers, #4 = data set
\tl_clear:N \l__joe_file_body_tl
\int_set:Nn \l__joe_file_rows_int
{
\int_div_truncate:nn { \seq_count:c { l_joe_file_#4_seq } + #1 - 1 } { #1 } % rounds
}
\int_step_inline:nnnn { 1 } { 1 } { \l__joe_file_rows_int }
{
\int_step_inline:nnnn { 0 } { 1 } { #1 - 1 }
{
\tl_put_right:Nx \l__joe_file_body_tl
{
\seq_item:cn { l_joe_file_#4_seq } { ##1 + ####1 * \l__joe_file_rows_int } &
}
}
\tl_put_right:Nn \l__joe_file_body_tl { \\ }
}
\begin{tabular}{ *{#1}{#2} l@{} }
\toprule
\prg_replicate:nn { #1 } { #3 & } \\
\midrule
\tl_use:N \l__joe_file_body_tl
\bottomrule
\end{tabular}
}
\ExplSyntaxOff
\usepackage{filecontents}
\begin{filecontents}{detJ.dat}
Move Det_J
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\end{filecontents}
\begin{document}
\begin{table}
\centering
\readfile{detJ.dat}{datain}
\processdata{datain}{dataout}{#1 #2}{#1 & #2}
\sisetup{group-digits=false}
\footnotesize
\maketable{3}{S[table-format=3.0]S[table-format=-1.7]}{{Movement}&{DetJ}}{dataout}
\end{table}
\end{document}
