Some issues when using the tabularx package

Question

Edit

Users @Mico and @WillieWong have taken much of their precious time explaining the nuances of the tabularx package to me and for which I will be ever so grateful. I now have a much better understanding of how it works, but I am more inclined to go with @Mico's suggestion, as I feel that, given my current LaTeX ability (which is not very high), I would be more comfortable with his; @WillieWong's is more succinct, but slightly out of my league (for now).

Thus, shown below is a minimal working example of my updated code, adapted from @Mico's answer:

\documentclass{article}
\usepackage[margin = 2.54 cm]{geometry}
\usepackage{array}
\usepackage{tabularx}
\usepackage{multirow}
\usepackage{amsmath}
\usepackage{amssymb}
\DeclareMathOperator{\E}{E}
\DeclareMathOperator{\Var}{Var}
\setlength{\tabcolsep}{12 pt}
\renewcommand{\arraystretch}{2}
\renewcommand{\tabularxcolumn}[1]{m{#1}}
\newcolumntype{B}{>{\bfseries}l}
\begin{document}
\section{Binomial Distribution}
\begin{flushleft}
\begin{tabularx}{\linewidth}{@{} B X @{}}
Abbreviation & $B(n, p)$ \
Type & Discrete \
Rationale & Sum of $n$ iid Bernoulli random variables \
Parameter(s) & $n\ \forall\ n \in \mathbb{Z^+}, p\ \forall\ p \in \mathbb{R}, 0 \leq p \leq 1$ \
Sample Space & $S = {0, \dots, n}$ \
Probability Mass Function & $f(x) = \binom n x p^x (1 - p)^{n - x}\ \forall\ x \in S$ \
Expectation & $\E(X) = np$ \
Variance & $\Var(X) = np(1 - p)$ \
Moment Generating Function & $M_X(t) = (1 - p + pe^t)^n$ \
Addition Rule & If $X_i \stackrel{\mathrm{iid}}{\sim} B(n_i, p), \mathrm{then} \sum\limits^k_{i = 1} X_i \sim B(n_1 + \dots + n_k, p)$ \
Relationship(s) & $B(1, p) = \mathrm{Bernoulli} (p)$ \
\multirow{2}{*}{Approximation(s)} & If $np$ and $np(1 - p)$ are both large, then $B(n, p) \approx \mathcal{N} (np, np[1 - p])$ \
& If $n$ is large but $np$ is small, then $B(n, p) \approx \mathrm{Pois} (np)$ \
\end{tabularx}
\end{flushleft}

The table now comes out like this:

As is evident when comparing both tables, my issues have been resolved and it is also noteworthy that I decided to stick with \multirow as opposed to using \newline for aesthetic purposes.

---

Context

I am quite new to LaTeX and am trying to write my own notes using it, but I am having some issues with formatting, particularly with the tabularx package.

Shown below is a minimal working example of my code:

\documentclass{article}
\usepackage[left = 2.54 cm, right = 2.54 cm, top = 2.54 cm, bottom = 2.54 cm]{geometry}
\usepackage{array}
\usepackage{tabularx}
\usepackage{multirow}
\usepackage{amsmath}
\usepackage{amssymb}
\begin{document}
\setlength{\tabcolsep}{18 pt}
\renewcommand{\arraystretch}{2}
\section{Binomial Distribution}
\begin{flushleft}
\begin{tabularx}{\linewidth}{@{}>{\bfseries}l X}
Abbreviation & $B(n, p)$ \
Type & Discrete \
Rationale & Sum of $n$ iid Bernoulli random variables $\forall\ n \in \mathbb{Z^+}$ \
Parameter(s) & $n, p\ \forall\ p \in \mathbb{R}, 0 \leq p \leq 1$ \
Sample Space & $S = {0, \dots, n}$ \
Probability Mass Function & $f(x) = \binom n x p^x (1 - p)^{n - x}\ \forall\ x \in S$ \
\multirow{2}{}{Moments} & $E(X) = np$ \
& $Var(X) = np(1 - p)$ \
Moment Generating Function & $M(t) = (1 - p + pe^t)^n$ \
Addition Rule & If $X_i \stackrel{iid}{\sim} B(n_i, p)\ \forall\ i \in \mathbb{Z^+}$, $i \leq k$, then $\sum\limits^k_{i = 1} X_i \sim B(n_1 + \dots + n_k, p)$ \
Relationship(s) & $B(1, p) =$ Bernoulli$(p)$ \
\multirow{2}{}{Approximation(s)} & If $np$ and $np(1 - p)$ are both large, then $B(n, p) \approx \mathcal{N} (np, np[1 - p])$ \
& If $n$ is large but $np$ is small, then $B(n, p) \approx$ Pois$(np)$ \
\end{tabularx}
\end{flushleft}
\end{document}

My table comes out like this:

Issues

Firstly, I realise that when the text in the second column is too long and gets wrapped by tabularx, the corresponding text in the first column is not automatically vertically center-aligned. Thus, my first question is, how can I tweak my code to vertically center-align both columns?

Secondly, my entire document is going to consist of many similar tables, where the first column will always be boldfaced. Thus, my second question is, how can I write some code, say, in the preamble (before I start any tables) to automatically boldface the first column of all tables?

P.S. I am self-learning LaTeX for school work (since my college degrees require a lot of mathematics), so if I have any "bad coding", please also feel free to suggest how I may improve :)

Answer 1

how can I tweak my code to vertically center-align both columns?

Choose the m ("middle") column type for the first column, and run \renewcommand{\tabularxcolumn}[1]{m{#1}} for the second column (which is supposed to have type X).

how can I write some code ... to automatically boldface the first column of all tables?

Just define a new column type called, say, B as follows:

\newcolumntype{B}[1]{>{\bfseries\RaggedRight}m{#1}}

if you want to limit the width of the column (and allow automatic line-wrapping, as needed). If you want don't want to permit line breaks -- and hence want to let the column to be (almost) arbitrarily wide -- just run

\newcolumntype{B}{>{\bfseries}l}

Observe that here, B does not take an argument.

\documentclass{article}
\usepackage[margin=2.54cm]{geometry}
\usepackage{tabularx}
\newcolumntype{B}[1]{>{\bfseries\RaggedRight}m{#1}}
\renewcommand{\tabularxcolumn}[1]{m{#1}}
\usepackage{amsmath,amssymb}
\DeclareMathOperator{\E}{E}  % define expectations and variance operators
\DeclareMathOperator{\Var}{Var}
\DeclareMathOperator{\Poiss}{Poiss}
\usepackage{ragged2e} % for '\RaggedRight' macro
\newlength\colwidth
\settowidth\colwidth{\textbf{Moment Generating}} % width of left-hand col.
\begin{document}
\setlength{\tabcolsep}{12pt} % 18pt seems excessive (default is 6pt)
\renewcommand{\arraystretch}{2}
\section{Binomial Distribution}
\begin{flushleft}
\begin{tabularx}{\linewidth}{@{} B{\colwidth} >{\RaggedRight}X @{}}
Abbreviation & $B(n, p)$ \
Type      & Discrete \
Rationale & Sum of $n$ iid Bernoulli random variables, $n \in \mathbb{N}^+$ \
Parameters & $n \in \mathbb{N}^+$, $0 \leq p \leq 1$ \
Sample Space & $S = {0, \dots, n}$ \
Probability Mass Function & $f(x) = \binom{n}{x} p^x (1 - p)^{n - x}\ \forall\ x \in S$ \
Moments & $\E(X) = np$\newline $\Var(X) = np(1 - p)$ \
Moment Generating Function & $M(t) = (1 - p + pe^t)^n$ \
Addition Rule & If $X_i \stackrel{\text{iid}}{\sim} B(n_i, p)\ \forall\ i \in \mathbb{Z}^+$, $i \leq K$, then $\sum\limits^K_{i = 1} X_i \sim B(n_1 + \dots + n_k, p)$ \
Relationship(s) & $B(1, p) = \textrm{Bernoulli}(p)$ \
Approximation(s) & If $np$ and $np(1 - p)$ are both large, then $B(n, p) \approx \mathcal{N} \bigl(np, np(1 - p)\bigr)$. \newline
 If $n$ is large but $np$ is small, then $B(n, p) \approx \Poiss(np)$. \
\end{tabularx}
\end{flushleft}
\end{document}

Answer 2

If you are going to be using the same formatting a lot, you can always define a new environment to encapsulate your tables. Below I defined the EMtable environment that wraps around tabularx. It takes one required argument, which is the column specifications for the 2nd through Nth columns.

• The environment locally renews the \tabularxcolumn specification to use m instead of p, and this makes vertical alignment as you desired. (By redefining it locally you can still use tabularx with the "regular" specification elsewhere in the document if you need to.
• The environment sets the first column always in l with bold font. It is up to you to specify the remaining columns (hence the required argument). Presumably you want to use something like XX if you have a total of 3 columns and so on.

\documentclass{article}
\usepackage[left = 2.54 cm, right = 2.54 cm, top = 2.54 cm, bottom = 2.54 cm]{geometry}
\usepackage{tabularx}
\usepackage{amsmath}
\usepackage{amssymb}
\newenvironment{EMtable}[1]{\flushleft\renewcommand\tabularxcolumn[1]{m{##1}}\tabularx{\linewidth}{@{}>{\bfseries}l #1}}{\endtabularx}
\begin{document}
\setlength{\tabcolsep}{18 pt}
\renewcommand{\arraystretch}{2}
\section{Binomial Distribution}
\begin{EMtable}{X}
Abbreviation & $B(n, p)$ \
Type & Discrete \
Rationale & Sum of $n$ iid Bernoulli random variables $\forall\ n \in \mathbb{Z^+}$ \
Parameter(s) & $n, p\ \forall\ p \in \mathbb{R}, 0 \leq p \leq 1$ \
Sample Space & $S = {0, \dots, n}$ \
Probability Mass Function & $f(x) = \binom n x p^x (1 - p)^{n - x}\ \forall\ x \in S$ \
Moments & $E(X) = np$ \newline
$Var(X) = np(1 - p)$ \
Moment Generating Function & $M(t) = (1 - p + pe^t)^n$ \
Addition Rule & If $X_i \stackrel{iid}{\sim} B(n_i, p)\ \forall\ i \in \mathbb{Z^+}$, $i \leq k$, then $\sum\limits^k_{i = 1} X_i \sim B(n_1 + \dots + n_k, p)$ \
Relationship(s) & $B(1, p) =$ Bernoulli$(p)$ \
Approximation(s) & If $np$ and $np(1 - p)$ are both large, then $B(n, p) \approx \mathcal{N} (np, np[1 - p])$ \newline
 If $n$ is large but $np$ is small, then $B(n, p) \approx$ Pois$(np)$\ 
\end{EMtable}
\begin{EMtable}{XX}
        Test & Some text & more text
\end{EMtable}
\end{document}

---

Since the OP expresses some interest in knowing how this works: very roughly speaking, for each cell, a reference line is computed. For standard single-line material in l, c, r, this is just that line itself:

OOOO

for material in p, this is the top line

OOOO
----
----

for material in b, this is the bottom line

----
----
OOOO

for material in m, this is the middle

----
OOOO
----

LaTeX tables try to set all the reference lines at the same height. So lp gives

OOOO    OOOO
        ----
        ----

and lb gives

        ----
        ----
OOOO    OOOO

(lm left as an exercise to the reader)

The tabularx environment basically uses X as a shorthand for p, but with automatically computed width. Changing the \tabularxcolumn specification as above makes X instead a shorthand for m, with the automatically computed width.

---

A few minor points:

• one nice thing about the tabularx package is that within an X cell you can use \newline (but not \\ !) to break lines; so you don't have to use multirow at least for your demonstrated example.
• The second call to EMtable just shows that you can make a three column version.