Aligning columns under a \multicolumn

Question

Edit: Modified the MWE and tried to give a better description of my problem

I'd like to be able to align columns under a multicolumn column header.

In the MWE I've just the data in the first table, and it appears how I expect it too, in the second table I've added a long column header.

I'd like to be able to modify the final two columns, such that the vertical divider appears midway through the "Very Long Column Name", and the final column in the last row does not get pushed into the center of the column.

This is the current output of the MWE

While this is what I'm after...

Thanks in advance!

\documentclass{article}

\usepackage[separate-uncertainty=true]{siunitx}

\begin{document}
  \begin{tabular}{l c l|l}
    Row 1 & & a  & b \\
    Row 2 & & \tablenum[table-format = 1.1]{1.2} & \tablenum[table-format = 1.1]{3.4} \\
  \end{tabular} \\

  \begin{tabular}{l c l|l}
    \multicolumn{1}{c}{Column Name} & \phantom{} & \multicolumn{2}{c}{Very Long Column Name} \\
    Row 1 & & a  & b \\
    Row 2 & & \tablenum[table-format = 1.1]{1.2} & \tablenum[table-format = 1.1]{3.4} \\
  \end{tabular}
\end{document}

Are line breaks allowed in the string "Very Long Column Name", or must the combined column be at least as wide as this string? Please advise. — Mico, Sep 11 '17 at 19:16
@Bernard, \tablenum comes from the siunitx package, it's not mine. — Andy, Sep 11 '17 at 19:23
What does "cannot" mean here? Do you mean "want not", or do you mean to say that you don't know how to insert line breaks? — Mico, Sep 11 '17 at 19:23
@Mico, Some of the column names in my document are images, so cannot be line broken. — Andy, Sep 11 '17 at 19:27
Sorry, but I have no idea what you're trying to achieve. It would be really helpful if you edited your posting and described both your document setup and the image-related issues in greater detail. Maybe somebody else will be able to help you. — Mico, Sep 11 '17 at 19:36

CarLaTeX · Accepted Answer · 2017-09-11T20:56:22.803

Like the second tabular here?

\documentclass{article}
\usepackage{graphicx}
\usepackage[separate-uncertainty=true]{siunitx}

\begin{document}
    \begin{tabular}{l c l|l}
        Row 1 & & a  & b \\
        Row 2 & & \tablenum[table-format = 1.1]{1.2} & \tablenum[table-format = 1.1]{3.4} \\
    \end{tabular} \\

    \begin{tabular}{l c}
        Column Name & Very Long Column Name \\
        \begin{tabular}{@{}l@{}}
            Row 1\\
            Row 2\\
        \end{tabular}
        &
        \begin{tabular}{@{}r|l@{}}
             a  & b \\
            \tablenum[table-format = 1.1]{1.2} & \tablenum[table-format = 1.1]{3.4} \\
        \end{tabular}
    \end{tabular}
\end{document}

Yes! Changing the @{}r|l@{} to @{}l|l@{} gives me exactly what I'm after! — Andy, Sep 11 '17 at 21:02

Aligning columns under a \multicolumn

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