WoW:API tinsert
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From TableLibraryTutorial of lua-users.org.
table.insert(table, [pos,] value) tinsert(table[, pos], value)
Insert a given value into a table. If a position is given insert the value before the element currently at that position:
> t = { 1,3,"four" }
> table.insert(t, 2, "two") -- insert "two" at position before element 2
> = table.concat(t, ", ")
1, two, 3, four
If no position is specified we append the value to the end of the table:
> table.insert(t, 5) -- no position given so append to end > = table.concat(t, ", ") 1, two, 3, four, 5
When a table has an element inserted both the size of the table and the element indices are updated:
> t = { 1,"two",3 } -- create a table
> = table.getn(t) -- find current size
3
> table.foreach(t, print) -- display the table contents
1 1
2 two
3 3
> table.insert(t, 1, "inserted") -- insert an element at the start
> = table.concat(t, ", ") -- see what we have
inserted, 1, two, 3
> = table.getn(t) -- find the size
4
> table.foreach(t, print) -- the indexes have been updated
1 inserted
2 1
3 two
4 3
When no position is specified the element is inserted at the end of the table according to the calculated size. The size of a table may be user specified and not reflect the number of elements, e.g.,
> t = { 1,"two",3; n=10 } -- create a table with user size
> table.insert(t, "end") -- insert with no position inserts at "end"
> table.foreach(t, print) -- display the table contents
1 1
2 two
3 3
11 end
n 11
Speed
If you are appending to an integer-indexed table, it is always faster to track the size yourself, as this example demonstrates (clocked on a 3Ghz P4)
local t = {}
local tinsert=table.insert
local b = os.clock()
local n=1
t.n=1
for i=1,5e6 do
table.insert(t, "") -- 2.25s - extra cost of looking up table. subkeys
tinsert(t, "") -- 2.02s - local function call is slightly faster
t[#t+1] = "" -- 1.72s - a lot of the cost seems to be #t
local tn=t.n; t[tn]=""; t.n=tn+1 -- 1.19s - storing "n" in the table
t[n]="";n=n+1 -- 0.88s - storing "n" in a local
t[i]="" -- 0.78s - cheat, we don't have "i" usually
-- empty -- 0.08s overhead for the loop
end
local e = os.clock()
print(e-b)