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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)
Parents
  • tweeks

    I'm confused about what exactly you're trying to do here.  An assoc list is usually a list of pairs, so you can ask for the keys (the first element), or the values (the second element), but asking for the 3rd, 4th, nth element doesn't make sense, because there are only two (right?).

     It looks like what you really want to do is get the nth elements in each sublist in a list of lists, which is very easy to do:

    > lists = '(("a" 1) ("b" 2))
(("a" 1) 
    ("b" 2)
)
> column = 0
0
> mapcar(lambda((list) nth(column list)) lists)
("a" "b")
> column = 1
1
> mapcar(lambda((list) nth(column list)) lists)
(1 2)
> lists = '(("a" 1) ("b" 2) ("c" 3 "see" 'more (columns)))
(("a" 1) 
    ("b" 2) 
    ("c" 3 "see" 
	(quote more) 
	(columns)
    )
)
> column = 2
2
> mapcar(lambda((list) nth(column list)) lists)
(nil nil "see")
> 
     
Reply
  • tweeks

    I'm confused about what exactly you're trying to do here.  An assoc list is usually a list of pairs, so you can ask for the keys (the first element), or the values (the second element), but asking for the 3rd, 4th, nth element doesn't make sense, because there are only two (right?).

     It looks like what you really want to do is get the nth elements in each sublist in a list of lists, which is very easy to do:

    > lists = '(("a" 1) ("b" 2))
(("a" 1) 
    ("b" 2)
)
> column = 0
0
> mapcar(lambda((list) nth(column list)) lists)
("a" "b")
> column = 1
1
> mapcar(lambda((list) nth(column list)) lists)
(1 2)
> lists = '(("a" 1) ("b" 2) ("c" 3 "see" 'more (columns)))
(("a" 1) 
    ("b" 2) 
    ("c" 3 "see" 
	(quote more) 
	(columns)
    )
)
> column = 2
2
> mapcar(lambda((list) nth(column list)) lists)
(nil nil "see")
> 
     
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