TikZ: How to split a tikzpicture into parts with a foreach-loop?

Question

If I have three parts of paths and nodes in a tikzpicture: what is the best way to split that up with a foreach-loop into 3 tikzpictures, where only one part is showing?
Like:
, ,

\documentclass[margin=5pt, tikz]{standalone}
\usepackage{tikz}

\begin{document}
\foreach \part in {1,...,3}{
\begin{tikzpicture}[
mystyle/.style={->, thin, font=\sffamily\tiny, blue, text=black, inner sep=0.5pt, very near start},
]
% 1:
\draw[mystyle] (140:1.2) -- +(0.6,0.05) node[mystyle, above]{1};

% 2:
\draw[mystyle, purple] (163:0.9) -- +(0.9,0.05) node[mystyle, above]{2};

% 3: 
\draw[mystyle, red, rounded corners=3] (200:0.6) -- ++(-0.3,-0.3) -- ++(0.4,-0.4) node[mystyle, below]{3};
\node[fill=red, circle, minimum width=2mm] at (210:0.1) {};
\end{tikzpicture}
}
\end{document}

Answer 1

You can use the undocumented discard layer of PGF for this as described in tikz: construct a phantom path. I wrapped it into a nice environment (which can't be nested).

\documentclass[margin=5pt, tikz]{standalone}
\usepackage{tikz}

\let\showonlyend\relax

\newenvironment{showonly}[2]{%
\ifnum#1=#2\else%
\let\showonlyend\endpgfonlayer
\pgfonlayer{discard}\fi
}{%
\showonlyend
}

\pgfdeclarelayer{discard}

\begin{document}
\foreach \p in {1,...,3}{
\begin{tikzpicture}[
mystyle/.style={->, thin, font=\sffamily\tiny, blue, text=black, inner sep=0.5pt, very near start},
]
% 1:
\begin{showonly}{\p}{1}
\draw[mystyle] (140:1.2) -- +(0.6,0.05) node[mystyle, above]{1};
\end{showonly}

% 2:
\begin{showonly}{\p}{2}
\draw[mystyle, purple] (163:0.9) -- +(0.9,0.05) node[mystyle, above]{2};
\end{showonly}

% 3: 
\begin{showonly}{\p}{3}
\draw[mystyle, red, rounded corners=3] (200:0.6) -- ++(-0.3,-0.3) -- ++(0.4,-0.4) node[mystyle, below]{3};
\node[fill=red, circle, minimum width=2mm] at (210:0.1) {};
\end{showonly}

\end{tikzpicture}
}
\end{document}

Answer 2

You can use if:

\documentclass[margin=5pt, tikz]{standalone}
\usepackage{tikz}

\begin{document}
\foreach \part in {1,...,3}{
\begin{tikzpicture}[
mystyle/.style={->, thin, font=\sffamily\tiny, blue, text=black, inner sep=0.5pt, very near start},
]
% 1:
\ifnum\part=1
    \draw[mystyle] (140:1.2) -- +(0.6,0.05) node[mystyle, above]{1};
\fi

% 2:
\ifnum\part=2
    \draw[mystyle, purple] (163:0.9) -- +(0.9,0.05) node[mystyle, above]{2};
\fi

% 3: 
\ifnum\part=3
    \draw[mystyle, red, rounded corners=3] (200:0.6) -- ++(-0.3,-0.3) -- ++(0.4,-0.4) node[mystyle, below]{3};
    \node[fill=red, circle, minimum width=2mm] at (210:0.1) {};
\fi
\end{tikzpicture}
}
\end{document}

== EDIT ==

As @Martin Scharrer♦ says the answer above is not what wanted.
You can achieve that using opacity:

\documentclass[margin=5pt, tikz]{standalone}
\usepackage{tikz}

\begin{document}
\foreach \a/\b/\c in {1/0/0, 0/1/0, 0/0/1}{
\begin{tikzpicture}[
mystyle/.style={->, thin, font=\sffamily\tiny, blue, text=black, inner sep=0.5pt, very near start},
]
% 1:
\draw[mystyle, opacity=\a] (140:1.2) -- +(0.6,0.05) node[mystyle, above]{1};

% 2:
\draw[mystyle, purple, opacity=\b] (163:0.9) -- +(0.9,0.05) node[mystyle, above]{2};

% 3: 
\draw[mystyle, red, rounded corners=3, opacity=\c] (200:0.6) -- ++(-0.3,-0.3) -- ++(0.4,-0.4) node[mystyle, below]{3};
\node[fill=red, circle, minimum width=2mm, opacity=\c] at (210:0.1) {};
\end{tikzpicture}
}
\end{document}