[Tex/LaTex] \arraybackslash doing on the table column

line-breakingtables

The \arraybackslash was used on answer table at How to auto adjust my last table column width, and why is there Underfull \vbox badness on this table?

\documentclass[10pt,a5paper,twoside]{memoir}
\usepackage[T1]{fontenc}

\usepackage[utf8]{inputenc}
\usepackage[brazil]{babel}

\usepackage{ragged2e}
\usepackage[showframe,pass]{geometry}

\usepackage{ltablex}
\keepXColumns

\begin{document}
\frenchspacing

\setlength\extrarowheight{2pt}
\begin{tabularx}{\linewidth}{|>{\RaggedRight}p{3cm}|>{\arraybackslash}X|}

    \caption{Formatação do texto}
    \label{tab:a_table_formatacao_de_texto} \\
    \hline
    \endfirsthead

    \multicolumn{2}{c}{\tablename~\thetable: Formatação do texto (continued)} \\
    \hline
    \endhead

    \hline
    \multicolumn{2}{r}{\footnotesize to be continued}
    \endfoot

    \hline
    \endlastfoot

    Cor                          & Branco -                              \\ \hline
    Formato do papel             & A5                                    \\ \hline
    Gramatura                    & 75                                    \\ \hline
    Cabeçalho                    & 0,7                                   \\ \hline
    Impressão                    & Frente e verso                        \\ \hline
    Margens                      & Espelhadas: superior 2, Inferior: 1,5 \\ \hline
    Cabeçalho                    & 0,7                                   \\ \hline
    Rodapé                       & 0,7                                   \\ \hline
    Paginação                    & Externa                               \\ \hline
    Alinhamento vertical         & Superior                              \\ \hline
    Cabeçalho                    & 0,7                                   \\ \hline
    Alinhamento do texto         & Justificado                           \\ \hline
    Cor                          & Branco -                              \\ \hline
    Formato do papel             & A5                                    \\ \hline
    Cabeçalho                    & 0,7                                   \\ \hline
    Gramatura                    & 75                                    \\ \hline
    Impressão                    & Frente e verso                        \\ \hline
    Margens                      & Espelhadas: superior 2, Inferior: 1,5 \\ \hline
    Rodapé                       & 0,7                                   \\ \hline
    Paginação                    & Externa                               \\ \hline
    Alinhamento vertical         & Superior                              \\ \hline
    Alinhamento do texto         & Justificado                           \\ \hline

\end{tabularx}

\end{document}

On the question Difference between \\ and \tabularnewline there is some explaining about it:

\arraybackslash: Restore \\ for use in array and tabular
environment (after \raggedright etc.).
 \def\arraybackslash{\let\\\tabularnewline}

Why \\ is broken by \raggedright and these etc other commands?

Reading the line \def\arraybackslash{\let\\\tabularnewline} seems the \\ is being redefined as \tabularnewline, does \raggedright and these etc other commands redefine it as something else, why?

Does I need to put \arraybackslash only on my last table column? What happens if I do not put it or put on/only a middle column or put on every column?

Best Answer

As with almost everything in TeX, control sequences (macros and control words) can be redefined, and because local grouping allows for local redefinition, the definitions of macros within a particular environment can be different from the definitions outside of that environment. This is the case of \\, which has multiple definitions depending on the environment.

In normal text, \\ is defined as:

\let \reserved@e \relax \let \reserved@f \relax \@ifstar 
 {\let \reserved@e \vadjust \let \reserved@f \nobreak \@xnewline }
 \@xnewline

Inside a tabular environment, it is defined as:

 \@tabularcr

which expands to:

 {\ifnum 0=`}\fi \@ifstar \@xtabularcr \@xtabularcr

Inside a raggedright environment, \\ is redefined to be

 \@centercr

which expands to:

 \ifhmode \unskip \else \@nolnerr \fi \par \@ifstar {\nobreak \@xcentercr }\@xcentercr

Since these definitions are different, after using a \raggedright environment in a tabular you need to use \arraybackslash to restore it to its tabular definition.

In addition to the question you linked to, see also:

What is the difference between \newline and \\?

Related Solutions

[Tex/LaTex] How to prevent hyphenation in a table column

Setting the text ragged right will do this for you. Something like

\usepackage{array}
...
\begin{tabular}{>{\raggedright}p{4cm}>{\raggedright\arraybackslash}p{4cm}}
Want to avoid hyphenation & also want to avoid hyphenation here \\
\end{tabular}

[Tex/LaTex] Sorting Table Column

I have no doubt that datatool is the way to go here. However, it is possible to use the code from my answer to the sorting question to do this.

You need to define a new comparator that compares only the first column. This particular implementation wants something that has a top level expansion into a row. E.g., you can define a macro for each row.

\def\rowi  {C & foo & qwer \\}
\def\rowii {A & bar & asdf \\}
\def\rowiii{B & baz & zxcv \\}

The goal is to be able to write the following to get sorted rows.

\begin{tabular}{lll}
\toprule
Letters & Metasyntatic variables & Gibberish\\
\midrule
\sortfirstcol{\rowi\rowii\rowiii}
\bottomrule
\end{tabular}

In particular, the \sortfirstcol{\rowi\rowii\rowiii} should expand to the sorted rows. As with \sortalpha, \sortfirstcol is just a simple macro that expands \sort with the comparator \sort@firstcol as its first argument.

\newcommand*\sortfirstcol{\sort\sort@firstcol}

The comparator isn't extremely complicated, but it does need to extract the first column of each argument. For that, we use a helper macro. And in keeping with the spirit of the original answer, this version is expandable.

\def\sort@firstcol#1#2{%
    \expandafter\expandafter\expandafter
        \sort@fc@helper\expandafter#1#2#1#2%
}

\def\sort@fc@helper#1&#2\\#3&#4\\#5#6#7{%
    \ifnumcomp{\pdfstrcmp{#1}{#3}}<{0}
    {#7{#5}{#6}}% else
    {#7{#6}{#5}}%
}

The \expandafters are going to expand the first two arguments a single time. For example, if the comparator is "called" as \sort@firstcol{\rowi}{\rowii}{...}, then it will expand to

\sort@fc@helper C & foo & qwer \\A & bar & asdf \\\rowi\rowii{...}

and so #1 will be the tokens "C ", #3 will be "A ", #5 will be \rowi, #6 will be \rowii, and lastly #7 will be the {...} that is the continuation that gets passed to the comparator.

From here, it's identical to \sort@alpha: it compares #1 and #3, passing #5 and #6 to the continuation.

Lastly, due to the representation of the rows, the \sortend and \sortoutput macros should be set to just expand to their argument:

\newcommand*\sortoutput[1]{#1}
\newcommand*\sortend[1]{#1}

The following is a complete example using the above code and the code from the previous answer.

\documentclass{article}
\usepackage{etoolbox}
\usepackage{booktabs}
\makeatletter
% #1 - comparator
% #2 - token list to sort
\newcommand\sort[2]{%
        \ifstrempty{#2}
        {}% else
        {%
                \sort@begin#1{}#2\sort@s\sort@begin
        }%
}

% helpers
\def\sort@s{\sort@s}
\def\ifsort@s#1{%
        \ifx\sort@s#1%
                \expandafter\@firstoftwo
        \else
                \expandafter\@secondoftwo
        \fi
}

% #1 - comparator
% #2 - tokens processed so far
% #3 - smallest token so far
% #4 - rest of the list
\def\sort@begin#1#2#3#4\sort@begin{%
        \ifsort@s{#4}
        {%
                \sortend{#3}%
                \sort#1{#2}%
        }% else
        {%
                \sort@go#1{#2}{#3}#4\sort@go
        }%
}

%     #1 - comparator
% #2 - tokens processed so far
% #3 - smallest token so far
% #4 - token under consideration
% #5 - rest of the list
\def\sort@go#1#2#3#4#5\sort@go{%
        #1{#3}{#4}{\sort@output#1{#2}{#5}}%
}
% #1 - comparator
% #2 - tokens processed so far
% #3 - rest of the list
% #4 - smaller of the two tokens
% #5 - larger of the two tokens
\def\sort@output#1#2#3#4#5{%
        \ifsort@s{#3}
        {%
                \sortoutput{#4}%
                \sort#1{#2{#5}}%
        }% else
        {%
                \sort@begin#1{#2{#5}}{#4}#3\sort@begin
        }%
}

\def\sort@numlt#1#2#3{%
        \ifnumcomp{#1}<{#2}
        {#3{#1}{#2}}% else
        {#3{#2}{#1}}%
}

\def\sort@numgt#1#2#3{%
        \ifnumcomp{#1}>{#2}
        {#3{#1}{#2}}% else
        {#3{#2}{#1}}%
}

\def\sort@alpha#1#2#3{%
        \ifnumcomp{\pdfstrcmp{#1}{#2}}<{0}
        {#3{#1}{#2}}% else
        {#3{#2}{#1}}%
}

\def\sort@firstcol#1#2{%
    \expandafter\expandafter\expandafter
        \sort@fc@helper\expandafter#1#2#1#2%
}

\def\sort@fc@helper#1&#2\\#3&#4\\#5#6#7{%
    \ifnumcomp{\pdfstrcmp{#1}{#3}}<{0}
    {#7{#5}{#6}}% else
    {#7{#6}{#5}}%
}

\newcommand*\sortnumlt{\sort\sort@numlt}
\newcommand*\sortnumgt{\sort\sort@numgt}
\newcommand*\sortalpha{\sort\sort@alpha}
\newcommand*\sortfirstcol{\sort\sort@firstcol}
\makeatother

% Change these to change out the sort outputs.
\newcommand*\sortoutput[1]{#1}
\newcommand*\sortend[1]{#1}

\begin{document}

\def\rowi  {C & foo & qwer \\}
\def\rowii {A & bar & asdf \\}
\def\rowiii{B & baz & zxcv \\}

\begin{tabular}{lll}
\toprule
Letters & Metasyntatic variables & Gibberish\\
\midrule
\sortfirstcol{\rowi\rowii\rowiii}
\bottomrule
\end{tabular}

\end{document}

Finally, I should point out that this representation (that is, rows as macros) isn't necessary. Due to the way \sort processes its arguments, one could easily write a comparator that allowed one to write the following.

\sortfirstcol{%
    {C & foo & qwer}%
    {A & bar & asdf}%
    {B & baz & zxcv}%
}
\def\sortoutput#1{#1\\}
\def\sortend#1{#1\\}

Perhaps I should have done that. The comparator would be slightly simpler.

Also, as implemented, a space at the beginning or end of the first column matters. One could probably deal with that too.

Best Answer

Related Solutions

[Tex/LaTex] How to prevent hyphenation in a table column

[Tex/LaTex] Sorting Table Column

Related Question