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Re: Mathematica behavior using highlighting and keyboard arrows - BUG???

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  • Subject: [mg98548] Re: [mg98522] Mathematica behavior using highlighting and keyboard arrows - BUG???
  • From: "David Park" <djmpark at>
  • Date: Sun, 12 Apr 2009 03:48:20 -0400 (EDT)
  • References: <18745390.1239440373119.JavaMail.root@n11>

It seems debatable as to which would be the better behavior.

The best way to select material from an Input or Output cell for copying is
to place the cursor at a position in the desired material and then use
successive Ctrl-. to select successively larger sub-expressions. 

David Park
djmpark at  

From: Bob F [mailto:deepyogurt at] 

I have been puzzled by the way that Mathematica handles highlighting
when using the keyboard arrow keys. For example if the cursor is in an
Input cell in the middle of any expression and you press and hold the
Shift key and then press the right-arrow key to highlight each
character for each press of the right-arrow key, and then if you
accidently go one or more characters too far (the repeat rate of the
key faster than my reaction time), and then I try and "back up" to the
intended correct position by letting go of the right-arrow key and
press the left-arrow key while still pressing the Shift, the
highlighting is extended to the left of the original starting
position, not the current position of the cursor, so instead of
correcting the "overshoot" you end up with even more unwanted
highlighted portion of an expression or text. And the most bizarre
thing about this is that the behavior is different depending on
whether it's a Text or an Input style cell, in that Input style cells
do it this way and Text style cells do it as I would expect.

The net result is that you have to start all over to correctly
highlight the portion of the cell expression you wanted to highlight
for subsequent Copy/Paste operation somewhere else for these Input

Is this a bug or a feature? Does this work the same on Windows and
Linux and all the other versions of Mathematica? I am on a Mac OS X

When you use the mouse to drag the current position cursor this
behavior does not occur either, in that there is an "original start
position" and as you drag the mouse to the left or right of this start
position, the intervening text is highlighted as you would expect. So
why the difference?

The Up/Down arrow keys DO NOT have this same behavior when trying to
highlight multiple cells, so this also seems inconsistent if this is a
feature rather than a bug.

I even looked up in the old Stephen Wolfram "Mathematica" book and it
talks about the using the arrow keys to highlight "two-dimensional
expressions" (on the bottom of page 180 if you wish to look), and it
says that the definitions for the arrow keys are "move to the next
character" for the right-arrow and "move to the previous character"
for the left-arrow. So on that basis it would appear this is indeed a
bug. I agree that it's not talking specifically about high-lighting,
but the fact that highlighting seems to break this definition of what
right-arrow and left-arrow do, seems to be another reason this
behavior a bug.

Would some of the people who have been using Mathematica for many,
many years please comment on whether this has always been the way this
highlighting with arrow keys has worked? Has it been this way since
version 1.0? If not, when did it change and why? What is the reason
for this seemingly inconsistent behaviour? (inconsistent between the
way highlighting works between left-right and up-down and mouse-
dragging highlighting)



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