How to make many columns blank in table easily?

Question

\documentclass{article}
\usepackage{booktabs}    
\begin{tabular{@{}ll|r|r|r|r|r|r|r|r|r|r|r|r|r|r|r|@{}}
A & B &&&&&&&&&&&&&&&\\%15 blank &
\end{tabular}

I want to do like the above where only first two column has value and others are blank.

For each row putting many & can possible to create the table.

Answer 1

You can replicate the & using details from Repeat command n times?:

\documentclass{article}

\usepackage{xparse}

\ExplSyntaxOn
\cs_new_eq:NN \Repeat \prg_replicate:nn
\ExplSyntaxOff

\begin{document}

\begin{tabular}{ @{} l l *{15}{|r} | @{} }
  A & B \Repeat{15}{& c} \\
  \Repeat{13}{&} & 1 & 2 & 3
\end{tabular}

\end{document}

A similar \Repeat macro is possible using multido:

\usepackage{multido}
\makeatletter
\renewcommand{\Repeat}[2]{%
  \def\@@x{}% Make sure \@@x is defined
  \multido{\i=1+1}{#1}{\protected@xdef\@@x{\@@x #2}}% Create global repetition
  \@@x% Execute repetition
}
\makeatother

Using \newcommand{\Repeat}[2]{\multido{\i=1+1}{#1}{#2}} won't work here because each cell within the tabular creates a group and the default definition of \multido doesn't make a global assignment of the stepping macro (\i). Instead, one has to assemble the repetition into a macro before executing it.

Also note the condensed way in which the column specification can be specified: *{<num>}{<col spec>} repeats <col spec> a total of <num> times.