Vrftjkry

I try to create a table in latex, however, the space between some columns is very unexpected.

Here is my working example:

begin{table}[H]

    centering

    begin{tabular}{c c c c c c}

    hline hline

    & & The title of my table is long & &  \ hline hline

     Criteria & M$_{1}$&  M$_{2}$ & M$_{3}$& M$_{4}$& M$_{5}$\

    1 & 1400 & 1450& 300 &3340 & \ 

    2 & & & & & \

    3 & & & & & 

    \ 

    hline 

    hline 

    end{tabular}

    caption{Caption}

    label{tab:my_label}

end{table}

If the title of the table is short then, there is no problem.

Any help, please?

Reason

The title of your table is considered as an element in Column 3.

Fix

documentclass{article}

begin{document}

begin{table}

    centering

    begin{tabular}{cccccc}

        hlinehline

        multicolumn{6}{c}{The title of my table is long}\ 

        hlinehline 

        Criteria & $M_1$ & $M_2$ & $M_3$ & $M_4$ & $M_5$ \ 

        1        & 1400  & 1450  & 300   & 3340  & 0     \

        2        &       &       &       &       &       \

        3        &       &       &       &       &       \

        hlinehline

    end{tabular}

    caption{Caption}

end{table}

end{document}

As @DũngVũ has already pointed out in this answer, the immediate cause of the problem is that you've assigned the string "The title of my table is long" to the third column of the six-column table. That third column is thus made as wide as is needed to display the title string.

One way to fix this issue is to let the title string span all 6 columns of the tabular environment, via a multicolumn{6}{c}{...} directive. This method "works", but only if the width of the title string is less than the width of the remaining tabular material. A second, and in my view more robust fix starts off by recognizing that the title string is, structurally speaking, part of the title of the table and that it should not be placed inside the tabular environment. Instead, it should be placed inside the argument of caption, and the caption statement should likely be placed above rather than below the tabular material.

While you're at it, you may also want to improve the "look" of the table by replacing the hline statements with toprule, midrule, and bottomrule -- macros provided by the booktabs package.

The following screenshot displays 3 tables: (1) the OP's original approach, (2) the fix achieved by using multicolumn, and (3) the fix achieved by moving the title outside of the tabular environment (and using the line-drawing macros of the booktabs package).

documentclass{article}

usepackage{booktabs}

usepackage[skip=0.333baselineskip]{caption} % optional

begin{document}



begin{table}[ht!]  %% OP's original code

    centering

    begin{tabular}{c c c c c c}

    hline hline

    & & The title of my table is long & &  \ 

    hline hline

    Criteria & M$_{1}$ & M$_{2}$ & M$_{3}$& M$_{4}$& M$_{5}$\

    1 & 1400 & 1450& 300 &3340 & 4400  \ 

    2 & & & & & \

    3 & & & & & \ 

    hline hline 

    end{tabular}

    caption{Caption}

    label{tab:my_label_1}

end{table}



begin{table}[h]  %% using multicolumn to fix the spacing issue

    centering

    begin{tabular}{c c c c c c}

    hline hline

    multicolumn{6}{c}{The title of my table is long}\ 

    hline hline

    Criteria & M$_{1}$&  M$_{2}$ & M$_{3}$& M$_{4}$& M$_{5}$\

    1 & 1400 & 1450& 300 &3340 & 4400  \ 

    2 & & & & & \

    3 & & & & & \ 

    hline hline 

    end{tabular}

    caption{Caption}

    label{tab:my_label_2}

end{table}



begin{table}[h]  %% using caption and the macros of the booktabs package

    caption{The title of my table}

    label{tab:my_label_3}

    centering

    begin{tabular}{@{} *{6}{c} @{}}

    toprule

    Criteria & Mtextsubscript{1}&  Mtextsubscript{2} & Mtextsubscript{3}& Mtextsubscript{4}& Mtextsubscript{5}\

    midrule

    1 & 1400 & 1450& 300 &3340 & 4400  \ 

    2 & & & & & \

    3 & & & & & \ 

    bottomrule

    end{tabular}

end{table}

end{document}