How to vertically align text in the headers of a PgfplotsTable?

Question

I am stacking one header by using this macro: \newcommand*{\textstackrel}[2]{\ensuremath{\stackrel{\hbox{#1}}{\hbox{#2}}}}. This makes the other single line headers bottom aligned, which looks bad.

So I tried a few multirow tricks I know to no avail, e.g.: assign column name/.code={\multicolumn{1}{c}{\multirow{2}{*}{#1}}}

Most of the time I ran into this error message:

! siunitx error: "duplicate-exponent-token"
! Duplicate exponent marker token '\token_to_str:N d' in input.

How do I do this correctly?

PS: MWE will follow when I have (more) time and if there is no answer before that.

Answer 1

While preparing the MWE I have found a possible solution. Feel free to improve it or post another one.

\documentclass{article}
\usepackage{multirow}
\usepackage{booktabs}
\usepackage{longtable}
\usepackage{siunitx}
\usepackage{pgfplots}
\usepackage{pgfplotstable}

\begin{document}

\pgfplotstableread{
size        min         max         avg         med
1           2e-03       3e-03       2.5e-03     2.4e-03
10          2.02e-03    3.02e-03    2.72e-03    2.32e-03
123456789   2.02        123.72e9    2.72e9      2.32e-03
}{\loadedtable}

\pgfplotstableset{
    begin table=\begin{longtable},
    end table=\end{longtable},
}
\sisetup{
    table-format = 3.2e+3,
    round-precision=2,
    round-mode=places,
    scientific-notation=engineering,
    group-digits=integer,
    group-separator={,},
    exponent-product = \cdot,
}

\pgfplotstabletypeset[
    header=true,
    string type,
    multicolumn names,
    columns={size,med,min,avg,max},
    assign column name/.code={%
        \pgfkeyssetvalue{/pgfplots/table/column name}{\multicolumn{1}{c}{\multirow{2}{*}{#1}} }%
    },
    columns/size/.style ={column name={\shortstack{Instance\\Size}}, column type={S[scientific-notation=false,table-format=9]}, int detect},
    columns/min/.style ={column name=Minimum,   column type=S},
    columns/avg/.style ={column name=Average,   column type=S},
    columns/med/.style ={column name=Median,    column type=S},
    columns/max/.style ={column name=Maximum,   column type=S},
    every head row/.style={before row=\toprule, after row=\\\midrule\endhead},
    every last row/.style={after row=\bottomrule},
]{\loadedtable}

\end{document}

The important bits are:

• to use \pgfkeyssetvalue in assign column name/.code, and
• the additional \\ line break in after row in the every head row style.