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list substitution problems

sparksu

I have a long list here:

listA=list(P1 P2 P3 ... Px-1 Px Px+1 ... Pn)

for a given Px, I want to substitute Px with 2 new elements Px1 Px2  :

ListB=list(P1 P2 P3 ... Px-1 Px1 Px2 Px+1 ... Pn)

I know how to do it using "reverse()" function.

But based on SKILL Language User Guide, reverse() can generate a lot of memeory.

Is there a more efficient way to do this? I don't care if it is destructive or nondestructive.

Here is my code using reverse():

;---------------------------------------------------------------------------------------------------------------------------------

listB2=rplaca(member(Px listA) Px2)                                     ;listB2=>list(Px2 ... Pn)

listB1=reverse(rplaca(member(Px2 reverse(listA) Px1)             ;listB1=>list(P1 P2 P3 ... Px-1 Px1)

listB=append(listB1 listB2)                ;ListB=>list(P1 P2 P3 ... Px-1 Px1 Px2 Px+1 ... Pn)

;---------------------------------------------------------------------------------------------------------------------------------

Parents

  • Something like this:

    match=nil
    foreach(map rem listA
      when(cadr(rem)==Px match=rem)
    )
    listA2=cdr(match)
    rplacd(match nil)
    listA1=listA

    Note this doesn't handle the case where the match is at the beginning of the list - but that's cheap to check for and handle, as I did in the previous response. Potentially you could make the foreach stop as soon as it finds a match by doing:

    prog(()
      foreach(map rem listA
        when(cadr(rem)==Px
          match=rem
          return()
        )
      )
    )

    The surrounding prog allows you to use return() to exit the foreach early.

    Regards,

    Andrew.

Reply

  • Something like this:

    match=nil
    foreach(map rem listA
      when(cadr(rem)==Px match=rem)
    )
    listA2=cdr(match)
    rplacd(match nil)
    listA1=listA

    Note this doesn't handle the case where the match is at the beginning of the list - but that's cheap to check for and handle, as I did in the previous response. Potentially you could make the foreach stop as soon as it finds a match by doing:

    prog(()
      foreach(map rem listA
        when(cadr(rem)==Px
          match=rem
          return()
        )
      )
    )

    The surrounding prog allows you to use return() to exit the foreach early.

    Regards,

    Andrew.

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