LaTeX/List Structures

Convenient and predictable list formatting is one of the many advantages of using LaTeX. Many users of wysiwyg word processors are frequently frustrated by the software's clumsy attempts to figure out when you intend lists to begin and end. This is the price of auto-formatting. As a mark-up language, LaTeX gives you far more control over the structure and content of your list. With a little practice you will find that creating lists in LaTeX is actually a pleasure when compared to wrestling with your typical "high power" word processor.

List Structures

Lists often appear in documents, especially academic, as their purpose is often to present information in a clear and concise fashion. List structures in LaTeX are simply environments which essentially come in three flavors: itemize, enumerate and description.

All lists follow the basic format:

\begin{list_type}
 
  \item The first item
  \item The second item
  \item The third etc \ldots
 
\end{list_type}

All three of these types of lists can have multiple paragraphs per item: just type the additional paragraphs in the normal way, with a blank line between each. So long as they are still contained within the enclosing environment, they will automatically be indented to follow underneath their item.

Itemize

This environment is for your standard bulleted list of items.

\begin{itemize}   \item The first item   \item The second item   \item The third etc \ldots \end{itemize}

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Enumerate

The enumerate environment is for ordered lists, where by default, each item is numbered sequentially.

\begin{enumerate}   \item The first item   \item The second item   \item The third etc \ldots \end{enumerate}

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Description

The description environment is slightly different. You can specify the item label by passing it as an optional argument (although optional, it would look odd if you didn't include it!). Ideal for a series of definitions, such as a glossary.

\begin{description}   \item[First] The first item   \item[Second] The second item   \item[Third] The third etc \ldots \end{description}

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Sometimes you want a description where the text begins on a new line. This cannot easily be done with \\. The trick is to use \hfill.

\begin{description}   \item[First] \hfill \\   The first item   \item[Second] \hfill \\   The second item   \item[Third] \hfill \\   The third etc \ldots \end{description}

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Nested Lists

Latex will happily allow you to insert a list environment into an existing one (up to a depth of four -- if you need more than four, use the easylist package). Simply begin the appropriate environment at the desired point within the current list. Latex will sort out the layout and any numbering for you.

\begin{enumerate}   \item The first item   \begin{enumerate}     \item Nested item 1     \item Nested item 2   \end{enumerate}   \item The second item   \item The third etc \ldots \end{enumerate}

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Customizing Lists

Customizing LaTeX is outside the beginners' domain. While not necessarily difficult in itself, because beginners are already overwhelmed with the array of commands and environments, moving on to more advanced topics runs the risk of confusion.

However, since the tutorial is on formatting, I shall still include a brief guide on customizing lists.

Compacted lists

As you may have noticed, in standard LaTeX document classes article, report or book but not amsart for example, the vertical spacing between items, and above and below the lists as a whole, is more than between paragraphs: it may look odd if the descriptions are too short.

Inside lists you can redefine some length/dimension variables of latex, for example using:

\begin{itemize}   \setlength{\itemsep}{1pt}   \setlength{\parskip}{0pt}   \setlength{\parsep}{0pt}   \item first item   \item second item \end{itemize} instead of \begin{itemize}   \item first item   \item second item \end{itemize}

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Alternatively, to create a unified look in your document you can define your own enumerate environment:

\newenvironment{my_enumerate}
{\begin{enumerate}
  \setlength{\itemsep}{1pt}
  \setlength{\parskip}{0pt}
  \setlength{\parsep}{0pt}}
{\end{enumerate}} If you want tightly-packed lists, use the mdwlist package (included in the mdwtools bundle), which provides compact, "starred" versions of the previous environments, i.e. itemize*, enumerate* and description*. They work exactly in the same way, but the output is more compact.

Alternatively, use the memoir class and with \tightlists.

Customizing Enumerated Lists

The thing people want to change most often with Enumerated lists are the counters. Therefore, to go any further, a brief introduction to LaTeX counters is required. Anything that LaTeX automatically numbers, such as section headers, figures, and itemized lists, there is a counter associated with it that controls the numbering.

There are four individual counters that are associated with itemized lists, each one represents the four possible levels of nesting, which are called: enumi, enumii, enumiii, enumiv. In order to reset any of these counters in the middle of an enumeration simply use \setcounter. The counter is incremented by \item before it is printed. For example to reset enumi use:

\begin{enumerate}
  \setcounter{enumi}{4}
  \item fifth element
\end{enumerate}

which prints as:

5. fifth element

Each counter also has a default format that dictates how it is displayed whenever LaTeX needs to print it. Such formats are specified using internal LaTeX commands:

Command	Example
\arabic	1, 2, 3 ...
\alph	a, b, c ...
\Alph	A, B, C ...
\roman	i, ii, iii ...
\Roman	I, II, III ...
\fnsymbol	Aimed at footnotes (see below), but prints a sequence of symbols.

Each counter entity holds various bits of information about itself. To get to the numbered element, simply use \the followed immediately (i.e., no space) by the name of the counter, e.g., \theenumi. This is often referred to as the representation of a counter.

Now, that's most of the technicalities out of the way. To make changes to the formatting of a given level:

\renewcommand{\representation}{\format_command{counter}}

Admittedly, the generic version is not that clear, so a couple of examples will clarify:

%Redefine the first level
\renewcommand{\theenumi}{\Roman{enumi}}
\renewcommand{\labelenumi}{\theenumi}
 
%Redefine the second level
\renewcommand{\theenumii}{\Alph{enumii}}
\renewcommand{\labelenumii}{\theenumii}

The method used above first explicitly changes the format used by the counter. However, the element that controls the label needs to be updated to reflect the change, which is what the second line does. Another way to achieve this result is this:

\renewcommand{\labelenumi}{\Roman{enumi}}

This simply redefines the appearance of the label, which is fine, providing that you do not intend to cross-reference to a specific item within the list, in which case the reference will be printed in the previous format. This issue does not arise in the first example.

Note that you can also add other symbols, such as parentheses and periods, before and after the counter. For instance, to create a list indexed by lower case letters with parentheses before and after the letter, you might enter the following:

\renewcommand{\labelenumi}{(\alph{enumi})}

Customizing Itemised Lists

Itemized lists are not as complex as they do not need to count. Therefore, to customize, you simply change the labels. It can be done manually for each entry with \item[new symbol], eg \item[$\star$].

The itemize labels are accessed via \labelitemi, \labelitemii, \labelitemiii, \labelitemiv, for the four respective levels.

\renewcommand{\labelitemi}{\textgreater}

The above example would set the labels for the first level to a greater than (>) symbol. Of course, the text symbols available in Latex are not very exciting. Why not use one of the ZapfDingbat symbols, as described in the Symbols section. Or use a mathematical symbol:

\renewcommand{\labelitemi}{$\star$}

Itemized list with tightly set items, that is with no vertical space between two consecutive items, can be created as follows.

\begin{itemize}
  \setlength{\itemsep}{0cm}%
  \setlength{\parskip}{0cm}%
  \item Item opening the list
  \item Item tightly following
\end{itemize}

Details of Customizing Lists

Note that it is necessary that the \renewcommand appears after the \begin{document} instruction so the changes made are taken into account. This is needed for both enumerated and itemized lists.

Inline lists

Inline lists are a special case as they require the use of the paralist package which provides the inparaenum environment (with an optional formatting specification in square brackets):

... \usepackage{paralist} \begin{document} \textbf{\itshape Inline lists}, which are sequential in nature, just like enumerated lists, but are \begin{inparaenum}[\itshape a\upshape)] \item formatted within their paragraph; \item usually labelled with letters; and \item usually have the final item prefixed with `and' or `or', \end{inparaenum} like this example. ...

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To change the styles of the counter, tokens A, a, I, i, and 1 can be used in the optional argument to produce the counter with one of the styles \Alph, \alph, \Roman, \roman and \arabic. For example:

\begin{inparaenum}[(i)]

produces the labels (i), (ii), (iii) ...