Re: Re: Getting values from a Plot

• To: mathgroup at smc.vnet.net
• Subject: [mg7495] Re: [mg7483] Re: Getting values from a Plot
• From: Allan Hayes <hay at haystack.demon.co.k>
• Date: Sat, 7 Jun 1997 03:48:14 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```There can be problems with using
Plot[....][[1,1,1,1]]
to get the list of coordinates when the plot is in two parts (eg.
Sqrt[x^2-1]), which we may not detect in advance, or when PlotStyle
has been used.
The alternative
Cases[Plot[....], Line[x]->x, Infinity]
deals with these.
Of course it will pick up all lines, for example, any from Epilog
and Prolog - these could be excluded by
Cases[Plot[....][[1]], Line[x]->x, Infinity]

(1) the plot may be in two parts.

pl = Plot[Sqrt[x^2-1],{x,-2,2}]

pl[[1,1]]
{Line[{{-2.,1.73205},...,{-1.00082,
0.0404806}}],
Line[{{1.00166,0.057683},...,{2.,1.73205}}]
}

We get the coordinates of only the first one

pl[[1,1,1,1]]

{{-2.,1.},{-1.83773,0.915277},... ,{-1.00082,0.0286183}}

(2) We may have used PlotStyle

pl2 =Plot[Sin[x],{x,-1,1},PlotStyle->Hue[0]]

pl2[[1]]
{Hue[0],{Line[{{-1.,-0.841471},...,{1.,0.841471}}]}}

Allan Hayes
hay at haystack.demon.co.uk
http://www.haystack.demon.co.uk/training/html
voice:+44 (0)116 2714198
fax: +44 (0)116 2718642
12 Copse Close, Leicester, LE2 4FB, UK

```

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