Assign the output of a loop [duplicate]

Question

Possible Duplicate:
Creating a table/Matrix during a For loop

Yet another simple question.

For[i = 1, i < 3, i++,
 For[j = 1, j < 3, j++,
   Print[{i, j}]
 ]
]

I want to assign the output to a list, for example like:

tts = {{1, 1}, {1, 2}, {2, 1}, {2, 2}}

All my efforts did not gave me the desired result, but I am sure it is possible. Any suggestions are welcome.

Answer 1

When you have some procedural style loop where you want to output things, you can often get quite good results using Sow and Reap:

 For[i = 1, i < 3, i++,
   For[j = 1, j < 3, j++,
     Sow[{i, j}]
   ]
 ]//Reap
 (* {Null, {{{1, 1}, {1, 2}, {2, 1}, {2, 2}}}} *)

Sow stores the expression it's given and when Reap is called, it will return a list where the first element is the result of the expression it was given, and the second argument is a collection of all the elements that where sowed during evaluation of that expression. Much more complex interaction is available if you look it up the doc, and often you can solve problems in an entirely procedural style and then just reap the results at the end, and perhaps reformat it if that is desired.

Answer 2

Mathematica tends to use print only for side effects. Also try to avoid the use of For.

You can just use the result of table to the variable.

tts=Table[{i,j},{i,1,3},{j,1,3}];

If you want to look at the contents of tts just enter it into a cell and press shift+return.