Re: Graphics Elements

*To*: mathgroup at smc.vnet.net*Subject*: [mg8817] Re: [mg8779] Graphics Elements*From*: Allan Hayes <hay at haystack.demon.co.uk>*Date*: Fri, 26 Sep 1997 00:33:41 -0400*Sender*: owner-wri-mathgroup at wolfram.com

Edwin Wright <edwin.wright at ns.sympatico.ca> [mg8779] Graphics Elements > Does anyone know (Version 2.1.0) how to delete graphics elements > from an existing graphic using AppendTo? Edwin: Consider the following (please enter the inputs to see the pictures) In[1]:= gr = Show[Graphics[{Circle[{0,0},1],Line[{{0,0},{1,1}}]}]] Out[1]= -Graphics- The graphics expression Graphics[{Circle[{0,0},1],Line[{{0,0},{1,1}}]}] has been displayed by using the function Show. The picture is a side effect. The output is hidden away in the special symbol -Graphics-. However, we can see it as follows In[2]:= InputForm[%] Out[2]//InputForm= Graphics[{Circle[{0, 0}, 1], Line[{{0, 0}, {1, 1}}]}] (It is just the expression that we used Show on; we have called it gr) Like any other Mathematica expression, we can manipulate it In[3]:= DeleteCases[gr,_Line, Infinity] (*remove any parts of the form Line[...]*) Out[3]= -Graphics- If we wish we cah see what has been done In[4]:= InputForm[%] Out[4]//InputForm= Graphics[{Circle[{0, 0}, 1]}] We can show the picture that this defines In[5]:= Show[%] Out[5]= -Graphics- We can alter the expression and show it with one line of code In[6]:= Show[gr/.Circle[p_,r_]:>{Hue[0],Circle[p-{1,0},r]}] Out[6]= -Graphics- 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 Leicester, UK