# Extract the x/y part from a coordinate in pgfplots

How can I extract only the x or y part of a predefined coordinate?

For instance, let's say we have

\coordinate (A) at (1,2);

And I want to use the x part of (A) like this

\draw (x of A,3)--(0,0);

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I'm not aware of any direct syntax to do that (though I would love to have one). You can however use the let operation (section 14.15 in the TikZ v2.10 manual):

\usetikzlibrary{calc}

[...]

\draw let \p1 = (A) in (\x1,3) -- (0,0);

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I thought at first that \pgfextractx should work with \coordinate, but it doesn't. –  Gonzalo Medina Mar 22 '11 at 2:19
@Gonzalo: \newdimen\mydim, \pgfextractx\mydim{\pgfpointanchor{A}{center}}. –  Caramdir Mar 22 '11 at 2:59
thank you; \pgfpointanchor is what I didn't know. –  Gonzalo Medina Mar 22 '11 at 16:01
You should point out that this requires the calc tikzlibrary. –  Martin Scharrer May 24 '11 at 18:42
@Martin: Thanks. –  Caramdir May 24 '11 at 19:23