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Alternative notation to [[i]], [[i,j]], etc. for the elements of a Table?

Gernot H
Posted 11 years ago

Hi,

since I am finding the notation {...}[[i]] or {{...},...{...}}[[i,j]], etc, to address the elements of Tables very cumbersome, I am looking for an alternative. Isn't there a possibility to enter the indices in a 2-D math way, as a subscript? All these square brackets make expressions often hard to overlook. I am wasting a lot of time hunting down bracket errors. This would be so much better in a 2-D notation.

Does anyone know such a way of notation? Thanks!
POSTED BY: Gernot H
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Bill Simpson
Bill Simpson
Posted 11 years ago
A word of caution, you may end up replacing your wasted time hunting down bracket errors with an even greater amount of wasted time hunting down subscript problems. There is even a tutorial that someone wrote to try to explain how to avoid some of the problems with subscripts

http://forums.wolfram.com/student-support/filedownload.cgi?CommentAttachment=1376428543-30335-4493.nb&CommentAttachmentName=SubscriptedVariables101.nb

and some have even advised not using these at all.

Subscripted variables are not "real variables", that has nothing to do with Real versus Complex numbers. I don't think anyone has ever really given the history of these, but my guess was that these were sort of glued onto the system after a lot of other incompatible and barely compatible decisions had been made and could not be changed.

Sometimes they work. In a complicated piece of code filled with subscripted variables that actually works I am always very surprised. In a complicated piece of code filled with subscripted variables that doesn't work the first thing I do is try to eliminate all the subscripts and see if the code works then.
POSTED BY: Bill Simpson
Gernot H
Gernot H
Posted 11 years ago
Hi everyone, and sorry for my late response! Somehow I did not get an Email notification that my question has been answered.)

Thank you all very much!

@ Bill Simpson: I will certainly have a look at this tutorial. Thanks!

@ Sander Huisman: I didn't know about all these ways yet! The one with the doubled "[" as a subskript works best for me, as this way the indices are well distinguishable from argument brackets! Thank you very much!
POSTED BY: Gernot H
Editing  KeyEventTranslations.tr, or any file deep inside Mathematica, is strongly discouraged and not supported.

I understand Mr. Horvat's wanting a shortcut, and it sounds like he is appropriately cautious. 
POSTED BY: Bruce Miller
Well, I would really like to know how to do this without modifying the installation directory.  Actually I asked about it here a while ago.

Please also take this as a feature suggestion/request for adding shortcuts for entering these characters.

Having used these shortcuts for several years, I know from experience that I'm less productive without them, and that having them makes Mathematica significantly more usable (mostly indirectly by allowing me to easily write more readable code).
POSTED BY: Szabolcs Horvát
David G
David G
Posted 10 years ago
POSTED BY: David G
Hi,

you can try to generalize the following idea:
f[arg_] := Module[{}, arg /. Subscript[a_, b_] :>  data[[b]]];

x_\[CircleDot]y_ := f[y];
data = {a, b, c};
f\[CircleDot]Subscript[x, 1]
f\[CircleDot]Subscript[x, 2]
f\[CircleDot]Subscript[x, 3]

I.M.
POSTED BY: Ivan Morozov
Completely agree with Bill's argument, such manipulations should be generally avoided.
I'm just curious, why the code below fails to work?
 In[4]:= data = {a, b, c};
 
 f[arg_] := Module[{}, arg /. Subscript[a_, b_] :> data[[b]]];
 Subscript[x_, y_] := Apply[f, {Subscript[x, y]}];
 Subscript[x, 1]
 
 During evaluation of In[4]:= $RecursionLimit::reclim: Recursion depth of 256 exceeded. >>
 During evaluation of In[4]:= $RecursionLimit::reclim: Recursion depth of 256 exceeded. >>
 During evaluation of In[4]:= $RecursionLimit::reclim: Recursion depth of 256 exceeded. >>
During evaluation of In[4]:= General::stop: Further output of $RecursionLimit::reclim will be suppressed during this calculation. >>
...
Out[7]= $Aborted
POSTED BY: Ivan Morozov
Bill Simpson
Bill Simpson
Posted 11 years ago
1. Evaluate Subscript[x,1]
2. which evaluates Subscript[x_,y_]
3. which evaluates Apply[f,{Subscript[x,y]}]
which starts step 2 all over again.

That doesn't even really rise to the level of criticizing Subscript, you need to find a completely incomprehensible Subscript failure to qualify for that.
POSTED BY: Bill Simpson
Thank you,  Bill, now it's clear to me
POSTED BY: Ivan Morozov
You can type it in many ways: You really need more??
POSTED BY: Sander Huisman
The very first thing I do after installing a new version of Mathematica is setting up keyboard shortcuts for typing the double brackets you get with ESC [[ ESC.

You can find the file named KeyEventTranslations.tr in the installation directory and add the following after the line EventTranslations[{
 Item[KeyEvent["[", Modifiers -> {Command}], FrontEndExecute[{FrontEnd`NotebookWrite[FrontEnd`InputNotebook[], "\[LeftDoubleBracket]", After]}]],
 Item[KeyEvent["]", Modifiers -> {Command}], FrontEndExecute[{FrontEnd`NotebookWrite[FrontEnd`InputNotebook[], "\[RightDoubleBracket]", After]}]], 

Do make a backup of the file before doing any modifications and put the backup outside of the Mathematica installation directory (or at least make sure you don't add extra files with a .tr extension).

On Windows/Linux I use the Control modifier instead of Command.

Now you can use Command-[ and Command-] to type these double brackets.  I'm so used to this at this point that I almost can't work at all with Mathematica without this modification.
POSTED BY: Szabolcs Horvát
POSTED BY: Rolf Mertig
Gustavo Delfino
Gustavo Delfino
Posted 10 years ago
POSTED BY: Gustavo Delfino
Douglas Kubler
Douglas Kubler
Posted 10 years ago
Attachments:
POSTED BY: Douglas Kubler

Szabolcs, the above for some reason did not work for me, 10.0.2, windows 7. In the notebook, the left [[ show OK, but not the ]] one. I type Alt-[ and now I see [[ added automatically, but when I type Alt-] the notebook inserts [] instead of ]] I modified the file

C:\Program Files\Wolfram Research\Mathematica\10.0\SystemFiles\FrontEnd\TextResources\Windows Now it looks like this: (had to do it as Admin on windows)

enter image description here

Restarted Mathematica. Type Alt-] and get [] instead of ]]

POSTED BY: Nasser M. Abbasi

Hi Nasser, this is because that shortcut is already defined in V10. See: http://reference.wolfram.com/language/tutorial/KeyboardShortcutListing.html

Try Ctrl instead of Cmd.

Or just use Get@"http://www.mertig.com" which does not modify the system KeyEventTranslations.tr at all.
POSTED BY: Rolf Mertig

As Rolf said, "Command" is a special key available only on Macs. On Windows I use Control instead of Command.
POSTED BY: Szabolcs Horvát

As Rolf said, "Command" is a special key available only on Macs. On Windows I use Control instead of Command.

No problem. it works now with Control. But it does say in the file the following:

(* Modifiers can be "Shift", "Control", "Command", "Option"
For Macintosh: "Command" = Command Key, "Option" = Option Key For X11: "Command" = Mod1, "Option" = Mod2

For Windows: "Command" = Alt, "Option" = Alt *)

Notice the last line. It says for windows "Command" = Alt, so that is why I left it as you had it, and used Alt to activate the Command. Any way. it is working now. thanks. Very useful trick.
POSTED BY: Nasser M. Abbasi

There are some reasons to use subscripts. For example, if I do symbolic solutions to problems with variables like x[1], x[2], and get rules such as x[1] -> expr1, etc. and then apply N to the rules, x[1] changes to x[1.], etc. That doesn't happen with subscripts.
POSTED BY: Frank Kampas

I think the OP was referring to a different application of subscripts ...

Regarding your note, I use SetAttributes[x, NHoldAll] for this situation.
POSTED BY: Szabolcs Horvát
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