Lua iterator to array - lua

Question

In Lua parlance, is there any syntactic sugar for turning an iterator function into an array (repeated invocations with results stored in ascending indices), perhaps something in the standard library ?
I'm tokenizing a string belonging to a protocol and need to to have positional access to elements at the start of the string, and the end of the string is a variant collection.
The code (specific to my use-case) is as follows, I find it hard to believe that it isn't in the standard library :d
local array_tokenise = function (line)
local i = 1;
local array = {};
for item in string.gmatch(line,"%w+") do
array[i] = item;
i = i +1
end
return array
end

Answer 1

There's no standard library function for it. But really, it's pretty trivial to write:
function BuildArray(...)
local arr = {}
for v in ... do
arr[#arr + 1] = v
end
return arr
end
local myArr = BuildArray(<iterator function call>)
This will only work if your iterator function returns single elements. If it returns multiple elements, you'd have to do something different.

Answer 2

As Nicol Bolas said, there is no standard library function that performs the action you desire.
Here is a utility function that extends the table library:
function table.build(build_fn, iterator_fn, state, ...)
build_fn = (
build_fn
or function(arg)
return arg
end
)
local res, res_i = {}, 1
local vars = {...}
while true do
vars = {iterator_fn(state, vars[1])}
if vars[1] == nil then break end
--build_fn(unpack(vars)) -- see https://web.archive.org/web/20120708033619/http://trac.caspring.org/wiki/LuaPerformance : TEST 3
res[res_i] = build_fn(vars)
res_i = res_i+1
end
return res
end
Here is some example code demonstrating usage:
require"stringify"
local t1 = {4, 5, 6, {"crazy cake!"}}
local t2 = {a = "x", b = "y", c = "z"}
print(stringify(table.build(nil, pairs(t1))))
print(stringify(table.build(nil, pairs(t2))))
print(stringify(table.build(
function(arg) -- arg[1] = k, arg[2] = v
return tostring(arg[1]).." = "..tostring(arg[2])
end
, pairs(t1)
)))
local poetry = [[
Roses are red, violets are blue.
I like trains, and so do you!
By the way, oranges are orange.
Also! Geez, I almost forgot...
Lemons are yellow.
]]
print(stringify(table.build(
function(arg) -- arg[1] == plant, arg[2] == colour
return (
string.upper(string.sub(arg[1], 1, 1))..string.lower(string.sub(arg[1], 2))
.. " is "
.. string.upper(arg[2]).."!"
)
end
, string.gmatch(poetry, "(%a+)s are (%a+)")
)))
Output:
{
[1] = {
[1] = 1,
[2] = 4,
},
[2] = {
[1] = 2,
[2] = 5,
},
[3] = {
[1] = 3,
[2] = 6,
},
[4] = {
[1] = 4,
[2] = {
[1] = "crazy cake!",
},
},
}
{
[1] = {
[1] = "a",
[2] = "x",
},
[2] = {
[1] = "c",
[2] = "z",
},
[3] = {
[1] = "b",
[2] = "y",
},
}
{
[1] = "1 = 4",
[2] = "2 = 5",
[3] = "3 = 6",
[4] = "4 = table: 00450BE8",
}
{
[1] = "Rose is RED!",
[2] = "Violet is BLUE!",
[3] = "Orange is ORANGE!",
[4] = "Lemon is YELLOW!",
}
stringify.lua can be found here

Answer 3

if you are just looking to auto-increment the table key for each data element, you can use table.insert(collection, item) - this will append the item to the collection and sets the key to the collection count + 1