4 replies to this topic

[ZagKalidor]

Think of a standard databank with f.e. Name, Adress, Postalcode, whatever, etc, that is saved to a file and (of course) is read at the start of the programs session.

Would a Pro save the entries in a chaotic way, in unalphabetic order, maybe in order like it's entered by the user and reorder it (in alphabetic ways) for screen output or would a pro save the file in an alphabetic order?

[Agent Silence]

you might need to be clearer on what you want done for me to understand

[Lyqyd]

If you're only ever going to sort it by one field, store it sorted by that field. If you're going to sort it by multiple different fields at different times based on user input, it probably isn't advantageous to store it sorted any particular way.

[ZagKalidor]

Thx

[hilburn]

Linked lists are your friend for something like this.
In case you don't know what these are you add a field to each entry called next, this indicates the next entry in the list. You can have multiple nexts, eg nextName, nextAddress, as well as prevName etc if you want. Then when it comes to printing it out, you can do so in order without having done any actual sorting.
An example implementation:

local llist={}
llist[1]={nextName=2,nextSurname=2}


local function addToList(entry)
    llist[#llist+1]=entry
    local thisName=1
    local thisSurname=1
    local nextNameEntry=llist[1].nextName
    local nextSurnameEntry=llist[1].nextSurname
    while llist[#llist].nextName==nil and llist[#llist].nextSurname==nil do
          if nextNameEntry>0 and (llist[nextNameEntry]=nil or llist[nextNameEntry].name>entry.name) then 
                 llist[#llist].nextName=llist[thisName].nextName
                 llist[thisName].nextName=#llist
                 nextNameEntry=-1
          elseif nextNameEntry>0 then
                 nextNameEntry=llist[thisName].nextName
          end
          if nextSurnameEntry>0 and (llist[nextSurnameEntry]=nil or llist[nextSurnameEntry].surname>entry.surname) then 
                 llist[#llist].nextSurname=llist[thisSurname].nextSurname
                 llist[thisSurname].nextSurname=#llist
                 nextSurnameEntry=-1
          elseif nextSurnameEntry>0 then
                 nextSurnameEntry=llist[thisSurname].nextSurname
          end          
     end
end

local function listByName()
    nextName=llist[1].nextName
    while nextName~=nil do
         print(llist[nextName].name.."  "..llist[nextName].surname)
         nextName=llist[nextName].nextName
     end
end

local function listBySurname()
    nextSurname=llist[1].nextSurname
    while nextSurname~=nil do
         print(llist[nextSurname].surname..",  "..llist[nextSurname].name)
         nextSurname=llist[nextSurname].nextSurname
     end
end

I'm pretty sure I've cocked up the implementation of addToList, but it shows you the general shape of how it works. Removing entries basically involves looping through the list and counting your position until your position gets to the entry you want to delete, then just link the previous entry to the next entry and it will vanish from the list (don't forget to set that entry to nil, but don't use table.remove as that will break everything)

They are a very powerful tool and well worth looking into