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Alternative way of getting the column in a list

essej
I have a function that gets the columns in an assoc list. Its working fine except for the very large size of list around 10 million. I gets a huge memory allocated when I profiled it.

procedure(getColSub(col lList)
  if(onep(length(col)) then
    case(car(col)
      (0 mapcar('car lList))
      (1 mapcar('cadr lList))
      (2 mapcar('caddr lList))
      (3 mapcar('cadddr lList))
      (t mapcar('nth vectorToList(makeVector(length(lList) car(col))) lList))
    )
  else
    mapcar('nth col vectorToList(makeVector(length(col) lList)))
  )
)

Example:
lList=list(list("a" 1) list("b" 2))
col=list(1 0) , gives ((1 "a")(2 "b"))
col=list(1) , gives (1 2)
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  • tweeks

    essej said:

    Again the problem is how to make it faster and less memory in a bigger size of list.

    mapcar alone takes a lot of memory and time

    Your version wastes considerable memory and time converting back and forth between vectors in the case where "col" is not a 1-element list.

    If you know the max number of columns in advance, just use vectors instead of lists.  You can get the nth element of a vector in constant time (while it's linear in the length of a list), and the memory usage should be smaller.

    If your data is sparse, use a table instead of a list or vector.

    What are you trying to do, anyway?  What do you have ten million of?

Reply
  • tweeks

    essej said:

    Again the problem is how to make it faster and less memory in a bigger size of list.

    mapcar alone takes a lot of memory and time

    Your version wastes considerable memory and time converting back and forth between vectors in the case where "col" is not a 1-element list.

    If you know the max number of columns in advance, just use vectors instead of lists.  You can get the nth element of a vector in constant time (while it's linear in the length of a list), and the memory usage should be smaller.

    If your data is sparse, use a table instead of a list or vector.

    What are you trying to do, anyway?  What do you have ten million of?

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