Hm, if your referring to creating hollow boxes in array like structures, that can best be achieved through array slicing, such as with numpy. Example:

import numpy

box = numpy.zeros((10,10),dtype='uint8')

box[1:5:,1:5:] = 1
box[2:4:,2:4:] = 0

print(box)

That produces this output:

[[0 0 0 0 0 0 0 0 0 0]
 [0 1 1 1 1 0 0 0 0 0]
 [0 1 0 0 1 0 0 0 0 0]
 [0 1 0 0 1 0 0 0 0 0]
 [0 1 1 1 1 0 0 0 0 0]
 [0 0 0 0 0 0 0 0 0 0]
 [0 0 0 0 0 0 0 0 0 0]
 [0 0 0 0 0 0 0 0 0 0]
 [0 0 0 0 0 0 0 0 0 0]
 [0 0 0 0 0 0 0 0 0 0]]

I don't know of a general solution to this problem, and your also talking like you want to extract features, e.g. walls versus floor.  The easy way is to just start at the top left and try expanding boxes right and/or down until you can't, then keep running the algorithm repeatedly on un-boxed tiles.  I haven't coded this myself but there's a few ways you can do it depending on how much time your algorithm has to run.  If the requirement of it being "the minimum number of boxes" isn't a hard requirement this will almost certainly give you something good enough, but it's hard to tell if this is a brain teaser/puzzle, or something you need for a project.

If it's for a game, though, consider a cross:

0, 1, 0
1, 1, 1
0, 1, 0

This obviously has a wall in the middle and 2 floor tiles, one on either side.  Do you want 2 floor tiles and a wall, or 1 floor and 2 wall tiles?  It seems to me that you'd want 1 wall and 2 separate chunks of floor for a game, as to not make the player figure out what subdivides it, but technically speaking either solution works.  If it's not just the minimum number of boxes but a specific minimal solution that gives friendly data for a radar or something in something like BK3, then you're going to get close but should be prepared to hand-edit the data afterword.  Especially for "fun" cases like: if you're climbing a tower, maybe you want the walls to be divided by the floors to highlight the vertical direction and what can be climbed to, rather than the floors divided by the walls to highlight the horizontal direction and what can be jumped.

If this is indeed game mapping--well. Ammo will be using semantic information coded in Lua as the maps in order to avoid this entire problem, at least if the prototypes that I haven't yet written work out.  If the prototypes don't work out then back to the drawing board.  But overall these days tilemaps make me sad inside, in the sense that if you do one you probably still need to mark it up afterword, or you're leaving a lot of things on the table.