This has probably been written in many projects, anyways here is the code I wrote up to convert a ruby table / 2-dimensional array / array of arrays to a tex table:

def to_tex(table, user_opts = {})
  default_opts = {:center => true, :sep_cols => true, :col_align => 'l'}
  opts = default_opts.merge(user_opts)
  lines = ['\begin{table}[!ht]']
  lines << '\begin{center}' if opts[:center]
  headers = table.first
  lines << "\\begin{tabular}{#{headers.map{opts[:col_align]}.join(opts[:sep_cols] ? '|' : '')}}"
  headers_in_bold = headers.map{|header| (header.nil? or header.empty?) ? '' : "\\textbf{#{header}}"}
  lines << headers_in_bold.join(' & ') + '\\\\ \\hline'
  table[1..-1].each{|row| lines << row.join(' & ') + '\\\\'}
  lines << '\end{tabular}'
  lines << '\end{center}' if opts[:center]
  lines << "\\caption{#{opts[:caption]}}" if opts[:caption]
  lines << "\\label{#{opts[:label]}}" if opts[:label]
  lines << '\end{table}'
  lines.join("\n")
end

The code assumes the first row is the header row and will put the column titles in bold. A horizontal line is put below the headers and then your rows are printed.

There are a some user definable options: the use of centering, caption, label, column alignment and the use of column separation. Some of them have a default value in the default_opts hash.

Usage example:

table = [[nil, 'Even?', 'Square']]
10.times{|i| table << [i, (i % 2 == 0) ? 'Y' : 'N', i**2]}
puts to_tex(table, :col_align => 'c', :caption => 'Table of numbers and basic properties')

This gives:

\begin{table}[!ht]
\begin{center}
\begin{tabular}{c|c|c}
 & \textbf{Even?} & \textbf{Square}\\ \hline
0 & Y & 0\\
1 & N & 1\\
2 & Y & 4\\
3 & N & 9\\
4 & Y & 16\\
5 & N & 25\\
6 & Y & 36\\
7 & N & 49\\
8 & Y & 64\\
9 & N & 81\\
\end{tabular}
\end{center}
\caption{Table of numbers and basic properties}
\end{table}

I hope this helps.