apply shift to nodes defined in foreach loop

Question

I would like to apply yshift effect to nodes defined with foreach loop. In below example,the output line not shift as expected:

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows,positioning,decorations.pathreplacing}
\begin{document}
\begin{tikzpicture}[
    box/.style={circle,draw,inner sep=1}
]
\def\arr{
  A/0,
  B/22mm,
  C/16mm
  }
\def\dy{4mm}
\foreach \name/\offset [count=\i from 0,evaluate=\i as \j using {int(\i-1)}] in \arr {
  \ifnum\i=0
    \node[box] (P\i) {\name};
  \else
      \node[box,right=\offset of P\j] (P\i) {\name};
  \fi
  }
\draw[-angle 90] ([yshift=\dy]P0) -- ([yshift=\dy]P2) node[pos=.5,sloped,above] {direction};
\end{tikzpicture}

\end{document}

Results:

Answer 1

If you specify .north, the line is shifted above the tops of the nodes.

\documentclass{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows,positioning,decorations.pathreplacing}
\begin{document}
\begin{tikzpicture}[
box/.style={circle,draw,inner sep=1}
]
\def\arr{
A/0,
B/22mm,
C/16mm
}
\def\dy{4mm}
\foreach \name/\offset [count=\i from 0,evaluate=\i as \j using {int(\i-1)}] in \arr {
\ifnum\i=0
\node[box] (P\i) {\name};
\else
\node[box,right=\offset of P\j] (P\i) {\name};
\fi
}
\draw[-angle 90] ([yshift=\dy]P0.north) -- ([yshift=\dy]P2.north) node[pos=.5,sloped,above] {direction};
\end{tikzpicture}

\end{document}

Answer 2

You could use transform canvas={yshift=\dy} to shift the whole line instead of just the coordinates:

\documentclass[border=1cm]{standalone}
\usepackage{tikz}
\usetikzlibrary{arrows,positioning,decorations.pathreplacing}
\begin{document}
\begin{tikzpicture}[
    box/.style={circle,draw,inner sep=1}
]
\def\arr{
  A/0,
  B/22mm,
  C/16mm
  }
\def\dy{4mm}
\foreach \name/\offset [count=\i from 0,evaluate=\i as \j using {int(\i-1)}] in \arr {
  \ifnum\i=0
    \node[box] (P\i) {\name};
  \else
      \node[box,right=\offset of P\j] (P\i) {\name};
  \fi
  }
\draw[transform canvas={yshift=\dy},-angle 90] (P0) -- (P2) node[pos=.5,sloped,above] {direction};
\end{tikzpicture}

\end{document}