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

GROUPS:
Hi,

since I am finding the notation {...}[] 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
Answer
10 months ago
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
Answer
10 months 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
Answer
10 months ago
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
Answer
10 months 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
Answer
10 months ago
Thank you,  Bill, now it's clear to me
POSTED BY: Ivan Morozov
Answer
10 months ago
You can type it in many ways: You really need more??

POSTED BY: Sander Huisman
Answer
10 months 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
Answer
9 months ago
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 Horvat
Answer
9 months ago
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
Answer
9 months ago
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 Horvat
Answer
9 months ago