Better selection tools to pick elements from groups (Feature #187)

\copygroup[n]{groupA}{groupB} copies the first n elements from groupA to groupB

I needed a command \pickgroup[n]{groupA}{groupB} very similar which would pick the n^th element from groupA and place to groupB.
Also I needed a command \rangegroup[n][m]{groupA}{groupB} to get the elements from 'n' to 'm' from groupA and place to groupB.

I wrote myself such commands by "rewording" \copygroup, but since I never programmed LaTeX before, maybe some of you guys could check it up.

Cheers,
Andrea

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\newcommand{\pickgroup}[3][1]{
  \AMCtok@max=#1\relax
  \ifnum\the\AMCtok@max<1
    \AMCtok@max=\csname #2@k\endcsname
  \fi
  \AMCtok@ik=\z@
  {\loop
    \advance\AMCtok@ik\@ne\relax%
      \ifnum\the\AMCtok@ik<#1\relax%
        \else
    \AMC@prepare@element{#3}%
        \global\csname #3@\romannumeral\AMCtok@k\endcsname=\csname #2@\romannumeral\AMCtok@ik\endcsname%
    \fi
  \ifnum\AMCtok@ik<\AMCtok@max\repeat}%
}
\newcommand{\rangegroup}[4][1]{
  \AMCtok@max=#2\relax%
  \ifnum\the\AMCtok@max<1%
    \AMCtok@max=\csname #3@k\endcsname%
  \fi%
  \AMCtok@ik=\z@%
  {\loop%
    \advance\AMCtok@ik\@ne\relax%
      \ifnum\the\AMCtok@ik<#1\relax%
        \else
    \AMC@prepare@element{#4}%
        \global\csname #4@\romannumeral\AMCtok@k\endcsname=\csname #3@\romannumeral\AMCtok@ik\endcsname%
    \fi
  \ifnum\AMCtok@ik<\AMCtok@max\repeat}%
}