tabu automatic / manual table width

Question

How can i let latex automatically choose the column width such that each entry does not go into \newline ? How can i manually set the width of each column while making sure that it all sums up to \columnwidth ?

\begin{table}[t]
    \begin{tabu} to \columnwidth { | X[l] || X[c] | X[c] | }
        \hline
        \textbf{Component} & \textbf{Time in ms} & \textbf{Time in \%} \\
        \hline
        Data processing & 42 & 33\\
        \hline
        RANSAC & 2 & 1 \\
        \hline  
        Region Proposals  & 82 & 64 \\
        \hline  
    \end{tabu}
    \caption{Breakdown in the running time our system with a single core machine. Time in ms is averaged across the validation set.}
    \label{tab:componentruntime}
\end{table}

Answer 1

Use good ol’ tabular* environment:

\documentclass[twocolumn]{article}

\usepackage{lipsum}

\begin{document}

\lipsum[2]

\begin{table}[htp]

\begin{tabular*}{\columnwidth}{  @{\extracolsep{\fill}} |l||c|c| @{} }
\hline
\textbf{Component} & \textbf{Time in ms} & \textbf{Time in \%} \\
\hline
Data processing & 42 & 33\\
\hline
RANSAC & 2 & 1 \\
\hline
Region Proposals  & 82 & 64 \\
\hline
\end{tabular*}

\caption{Breakdown in the running time our system with a single core 
  machine. Time in ms is averaged across the validation set.}
\label{tab:componentruntime}

\end{table}

\lipsum

\end{document}

The mandatory version with booktabs and no vertical rule. The left alignment in the first column makes the double vertical rule unnecessary (it never is, actually). Since entries are not split across lines, the horizontal rules can be reduced to a bare minimum.

\documentclass[twocolumn]{article}
\usepackage{booktabs}

\usepackage{lipsum}

\begin{document}

\lipsum[2]

\begin{table}[htp]

\begin{tabular*}{\columnwidth}{  @{\extracolsep{\fill}} lcc @{} }
\toprule
\textbf{Component} & \textbf{Time in ms} & \textbf{Time in \%} \\
\midrule
Data processing & 42 & 33\\
RANSAC & 2 & 1 \\
Region Proposals  & 82 & 64 \\
\bottomrule
\end{tabular*}

\caption{Breakdown in the running time our system with a single core 
  machine. Time in ms is averaged across the validation set.}
\label{tab:componentruntime}

\end{table}

\lipsum

\end{document}

By also loading siunitx you can easily get alignment for the figures.

\documentclass[twocolumn]{article}
\usepackage{booktabs}
\usepackage{siunitx}

\usepackage{lipsum}

\begin{document}

\lipsum[2]

\begin{table}[htp]

\begin{tabular*}{\columnwidth}{
  @{\extracolsep{\fill}}
  l
  S[table-format=2.0]
  S[table-format=2.0]
  @{}
 }
\toprule
\textbf{Component} & \textbf{Time in ms} & \textbf{Time in \%} \\
\midrule
Data processing & 42 & 33\\
RANSAC & 2 & 1 \\
Region Proposals  & 82 & 64 \\
\bottomrule
\end{tabular*}

\caption{Breakdown in the running time our system with a single core 
  machine. Time in ms is averaged across the validation set.}
\label{tab:componentruntime}

\end{table}

\lipsum

\end{document}