Creating an array with "For" loop

Question

I need to perform a number of operations within a For loop and store the results in an indexed array (without using the Append function) For examole (to make it simple), I need to find the square of numbers i = 1 to 5 and sore it in y[i]. In precedural languages it would look like:

   for i = 1,5,i++,
        y(i)=i^2
    end

To implement this in Mathematica I tried this code:

 For[i = 1, i <= 5, i++,
    y[[i]] = i^2;  
    ]

which failed. Is there a way to create such array (y)?

Do you understand why it failed? y is not defined, so you can't access y[[i]]. Try defining y before and it works (for that, see e.g. ConstantArray). Edit My comment assumes, as you state, that you need to use For. Otherwise that's much simpler with Table. — anderstood, Mar 23 '18 at 16:44
Thanks for your reply.The problem is that I am using images and applying many functions (filtering, image processing, etc..) and then storing the final result in an array for comparison. To me, the simplest way would be to use a For loop and run the full code repeatedly on each image. — Heba Sea, Mar 23 '18 at 17:05
Then you should look up Map[] or Table[] as already suggested, if you have a list of images. If you really must loop, use Do[] instead. — J. M.'s missing motivation, Mar 23 '18 at 17:09
If OP is doing image processing OP should probably be using at least some of Mathematica's image processing functions: Blur, a whole host of Filters, etc. — High Performance Mark, Mar 23 '18 at 20:33

score 1 · Answer 1 · answered Mar 23 '18 at 16:48

1

y = Range[5]; (* y needs to be predefined as anderstood pointed out *)
For[ i = 1, i <= 5, i++,
  (* body *)
  y[[i]] = i^2
]

If it has to be For...

y
(* {1, 4, 9, 16, 25} *)

answered Mar 23 '18 at 16:48

gwr

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Thank you so much! – Heba Sea Mar 23 '18 at 16:52
2

@HebaSea You are welcome. Be sure to look up the alternatives given in the comments above. For really is no fit for Mathematica. – gwr Mar 23 '18 at 16:56

Creating an array with "For" loop

1 Answers1