> From: Mike Day
> Though there should be
> some csv file routines in the example J scripts provided with
> your installation if you're using that format.

Depending on the format of your file of numbers you might find the 'tables/dsv' 
addon useful for 
reading and writing delimited values to and from a file:
<http://www.jsoftware.com/jwiki/Addons/tables/dsv>

Following in Mike's footsteps:
   load 'tables/dsv'
   ]array=: makenum ' ' readdsv 'c:\user\data.txt'
0 1 2
3 4 5
6 7 8

   ]array2=: 30+i.3 3  NB. create another array
30 31 32
33 34 35
36 37 38

   ]rndposit=: 3 3...@$2  NB. create mask of cells to change
1 0 0
0 1 1
0 0 0

   ]newarray=: rndposit}array,:array2  NB. another amend syntax
30  1  2
 3 34 35
 6  7  8

   newarray writedsv 'c:\user\newdata.txt';' '
24
NB. 24 bytes written to c:\user\newdata.txt using space-delimited newarray.

Here are a couple of variations on the amend usage illustrated above:
   (2|array)}array,:_1  NB. replace odd members of array with _1
 0 _1  2
_1  4 _1
 6 _1  8

   ]array3=: i. 3 4
0 1  2  3
4 5  6  7
8 9 10 11

   (3|array3)}(array3,:_1),3 4...@$0
       0       _1 0.817135       3
      _1 0.443886        6      _1
0.629304        9       _1 0.41772

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