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Mathematica 9: bug in merging cells

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  • Subject: [mg128930] Mathematica 9: bug in merging cells
  • From: Fred Simons <f.h.simons at tue.nl>
  • Date: Tue, 4 Dec 2012 04:14:30 -0500 (EST)
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When writing a larger program, I usually test the single steps in 
separate cells, then merge these cells and localize the variables by 
wrapping the contents of the merged cells in a Module. By doing so in 
Mathematica 9, due to a bug in merging cells, I lost a lot of code. I 
reported this bug to WRI two weeks ago. It is not yet repaired in the 
new release, so I thought I would mention this annoying bug here as well.

This is an example (Mathematica 9 for Windows, I am not aware if this 
happens for other systems too).

Construct two input cells, the first one containing

a=1;
(* comment *)
b=2;

and the second one

c=3;

When merging these two cells the contents ending with the comment is 
shown in an orange rectangle, with the error message that there is a 
RowBox with an invalid first argument. I cannot see any reason why this 
merging of cells could not be undone with ctrl-Z, but it cannot and 
therefore part of my code was gone.

In this simple example I could see how to fix it. Toggle ctrl-E for 
seeing the box structure. Place a } just behind the RowBox with the 
comment  and a { behind the very first RowBox[, that is followed on the 
next line with another RowBox.

During writing this message, I found that the same happens when you try 
to copy and paste the first cell.

Fred Simons
Eindhoven University of Technology



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