[Haskell-cafe] How to devide matrix into small blocks

[Janis Voigtlaender]

Henning Thielemann wrote:
> On Wed, 13 Jun 2007, L.Guo wrote:
> 
> 
>>I already have one matrix of type [[a]] to store one image.
>>
>>What I want to do is to devide the image into severial small blocks in same size.
>>
>>To do that, I wrote this tool function.
>>
>>chop      :: Int -> [a] -> [[a]]
>>chop _ [] = []
>>chop n ls = take n ls : chop n (drop n ls)
> 
> 
> I assume that it is more efficient to use 'splitAt' instead of 'take' and
> 'drop'.
> 
> 
>>But I do not know how to use it to write the function.
> 
> 
> chop blockHeight (map (chop blockWidth) image)

That would divide

abcd
efgh
ijkl
mnop

into

[
[
ab
cd
,
ef
gh
]
,
[
ij
kl
,
mn
op
]
]

at block size 2. In any case, the original poster was not very clear
about what they want...

-- 
Dr. Janis Voigtlaender
http://wwwtcs.inf.tu-dresden.de/~voigt/
mailto:voigt at tcs.inf.tu-dresden.de