Am Samstag, 21. Februar 2009 23:58 schrieb Daniel Fischer:
Am Samstag, 21. Februar 2009 23:29 schrieb Thomas Davie:
How about this:
maxTableColumnWidths :: [[String]] -> [Int] maxTableColumnWidths = map (maximum . map length)
That's not what he needs,
maxTableColumnWidths = map (maximum . map length) . transpose
would be it. But I'm afraid that wouldn't solve his memory problems.
Regarding the memory problems: String is rather a memory hog anyway. Keith, have you considered using ByteStrings? That might solve your memory problems with a straightforward algorithm.
Also, if the rows can contain many columns, it is wasteful to calculate the length of prevMaxValues for every row. You could either have that as a parameter, or use a custom zipWith:
zipWithD :: (a -> a -> a) -> [a] -> [a] -> [a] zipWithD f (x:xt) (y:yt) = f x y:zipWithD f xt yt zipWithD _ [] ys = ys zipWithD _ xs [] = xs
Then maxRowFieldWidths would become
maxRowFieldWidths row prev = zipWithD max (map length row) prev
or, pointfree:
maxRowFieldWidths = zipWithD max . map length
seqList can also be written as
seqList = foldr seq False
That would make
maxTableColumnWidths = foldr ((seqList .) . zipWithD max) []
Ouch! Of course not seqList, but an analogous function that returns the list itself. evalList xs | seqList xs = undefined | otherwise = xs maxTableColumnWidths = foldr ((evalList .) . zipWithD max) []
I'm not sure if that is strict enough, though.
Also, you might try
maxTCWs = foldr seq [] . foldr (zipWithD max) []
Oops! No good either. I must be too tired :( maxTCWs = evalList . foldr (zipWithD max) []
, but I expect that to be a bad memory citizen.
Bob
Cheers, Daniel