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Maintaining Lua array order for a priority queue?

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Posted by Rivius (99 posts) Bio

Date

Wed 20 Apr 2011 02:49 PM (UTC)

Amended on Wed 20 Apr 2011 02:50 PM (UTC) by Rivius

Message

I basically have a function that adds values to an array and performs functions on it, but I wish to perform these functions in the order that they appear. Here is an example:


test = {}

test["apples"] = "fruit"
test["spider"] = "insect"
test["dog"] = "pet"

for a,b in pairs (test) do
print(a)
end

Will not return a print in the order that I made the table. Is there a good, simple way to keeping these organized so that I can make a priority queue for my curing?

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Posted by Twisol USA (2,257 posts) Bio

Date Reply #1 on Wed 20 Apr 2011 06:29 PM (UTC)

Message

Tables are inherently orderless. You'll want to use numeric indices if you want any kind of order:

local test = {}

test[#test+1] = {"apples", "fruit"}
test[#test+1] = {"spider", "insect"}
test[#test+1] = {"dog", "pet"}

for a,b in ipairs(test) do
  print(b[1])
end

Of course, this means "apples", "spider", and "dog" are no longer keys, but if you have a priority queue I don't expect you want to get things by particular keys and you just want to go in order. Also, ipairs() is an iterator that goes from test[1], test[2], etc. to the first entry that's nil (which in this case would be test[4])

'Soludra' on Achaea

Blog: http://jonathan.com/
GitHub: http://github.com/Twisol

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Posted by Nick Gammon Australia (23,046 posts) Bio Forum Administrator

Date Reply #2 on Thu 21 Apr 2011 12:42 AM (UTC)

Message

Please see the forum thread: http://gammon.com.au/forum/?id=6036.

In there it describes the "pairsbykeys" module. That ships with MUSHclient.

Example:


require "pairsbykeys"

test = {}

test["apples"] = "fruit"
test["spider"] = "insect"
test["dog"] = "pet"

for a,b in pairsByKeys (test) do
  print(a)
end

Output:


apples
dog
spider

(re-reads initial post)

Well in your case, as Twisol said, you just do a table.insert (or his technique):


local test = {}

table.insert (test, {"apples", "fruit"})
table.insert (test, {"spider", "insect"})
table.insert (test, {"dog", "pet"})
 

for a,b in ipairs(test) do
  print(b[1])
end

Output:


apples
spider
dog

The Lua developers recommend Twisol's approach, personally I think table.insert makes your intentions clearer.

- Nick Gammon

www.gammon.com.au, www.mushclient.com

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Posted by

Twisol USA (2,257 posts) Bio

Date

Reply #3 on Thu 21 Apr 2011 03:07 AM (UTC)

Message

As it happens, I just forgot what the function was called. :D

'Soludra' on Achaea

Blog: http://jonathan.com/
GitHub: http://github.com/Twisol

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Posted by

Rivius (99 posts) Bio

Date

Reply #4 on Thu 21 Apr 2011 01:09 PM (UTC)

Message

Hrm. Alrighty. Feels a bit messy, but I'll play around with it and see if I have any further questions. Thanks guys :)

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Posted by Rivius (99 posts) Bio

Date Reply #5 on Sat 23 Apr 2011 04:39 PM (UTC)

Message

Alright, how about doing it this way then.
affs = {}
cures = {}

queue =
{
"health_low",
"mana_low",
"paralysis",
"health_medium",
"mana_medium"
}

cures["health_low"] = "sip health"
cures["mana_low"] = "sip mana"
cures["paralysis"] = "focus body"

for a in ipairs (queue) do
if affs[queue[a]] then
send(cures[[queue[a]])
end
end

it seems to be curing fine and in order, but with such a small queue I'm wondering if it's partially by luck, but someone said ipairs with a simple table with no keys keeps it in order. Is this true? If so, I might just use that solution instead.

One thing I was wondering is if I had multiple cures listed though like:

cures["paralysis"] = {focus body, sip allheale}

I'd want to run through that list and only send one. That is, not focus body and sip allheale at the same time for the same cure. Since I check my cures on each prompt, I'm scared I'll try to focus body on one, then sip allheale on another or even try to do both at the same time.

How would I pick just one from this new mini table? I guess I would just do another for loop inside there?

for a in ipairs cures[queue[a]] do
send(cures[queue[a]]
end

This would make it loops through all the cures in the list. I was thinking instead of sending things to the world, I'd make the keys functions in that table, and these functions would check for balances, so I wouldn't send things off balance...something like this:

function focus_body()
if balance.focus = true then
Send("focus body")
balance.focus = false
end
end

function sip_allheale()
if balance.allheale = true then
Send("sip allheale")
balance.allheale = false
end
end

cures["paralysis"] = { function () sip_allheale() end, function focus_body() end}

and then do the loop

for a in ipairs cures[queue[a]] do
cures[queue[a]]()
end

That means I'll send only the cures that are onbalance, but I'd still send them both if they were offbalance. I'm also thinking that maybe my inexperience with lua makes it hard to see a better way that a for loop within a for loop, so is there a better way?

Final code would end up like this:


affs = {}
cures = {}

queue = 
{
"health_low",
"mana_low",
"paralysis",
"health_medium",
"mana_medium"
}

function focus_body()
if balance.focus = true then 
Send("focus body")
balance.focus = false
end
end

function sip_allheale()
if balance.allheale = true then 
Send("sip allheale")
balance.allheale = false
end
end

cures["paralysis"] = { function () sip_allheale() end, function focus_body() end}

for a in ipairs (queue) do
if affs[queue[a]] then
for a in ipairs cures[queue[a]] do
(cures[queue[a]]()
end
end
end

looks sloppy, and I'm sure I'll be trying to cure the same twice.

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Posted by Nick Gammon Australia (23,046 posts) Bio Forum Administrator

Date Reply #6 on Sat 23 Apr 2011 11:49 PM (UTC)

Message

Try indenting, it makes debugging so much easier:


affs = {}
cures = {}

queue = 
  {
  "health_low",
  "mana_low",
  "paralysis",
  "health_medium",
  "mana_medium"
  }

function focus_body()
  if balance.focus = true then 
    Send("focus body")
    balance.focus = false
  end
end

function sip_allheale()
  if balance.allheale = true then 
    Send("sip allheale")
    balance.allheale = false
  end
end

cures["paralysis"] = { 
            function () 
              sip_allheale() 
            end, 
            function 
              focus_body() 
            end}

for a in ipairs (queue) do
  if affs[queue[a]] then
    for a in ipairs cures[queue[a]] do
      (cures[queue[a]]()
    end
  end
end

I don't think what you have is too bad, the inner loop is just iterating through a short list of functions you want to perform.

- Nick Gammon

www.gammon.com.au, www.mushclient.com

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