I have these tables set like this
local tableone = {["Gold"] = 10, ["Gem"] = 5}
local tabletwo = {["Level"] = 1}
This is the code for merging
local test = {tableone, tabletwo}
print(test)
But if I try to merge the tables then the output is like this
[1] = {
["Gold"] = 10,
["Gem"] = 5
},
[2] = {
["Level"] = 1
}
And I would like to have the output like this
[1] = {
["Gold"] = 10,
["Gem"] = 5,
["Level"] = 1
}
Is this possible?
Sorry if I'm not that good at explaining.
You can do this with a simple nested loop.
local function merge(...)
local result <const> = {}
-- For each source table
for _, t in ipairs{...} do
-- For each pair in t
for k, v in pairs(t) do
result[k] = v
end
end
return result
end
local t <const> = {merge(tableone, tabletwo)}
I put the result in a table constructor due to the [1] in the question.
Related
In this code:
t = {
num = '',
}
t[0].num = '0'
t[1].num = '1'
t[2].num = '2'
Is there a way for me to delete t[0], then shift all of the table's values down, so that afterword it looks like this:
t[0].num = '1'
t[1].num = '2'
Example with imaginary functions:
t = {
num = '',
}
t[0].num = '0'
t[1].num = '1'
t[2].num = '2'
for i=0,tableLength(t) do
print(t[i])
end
--Output: 012
remove(t[0])
for i=0,tableLength(t) do
print(t[i])
end
--Output: 12
t = {
num = '',
}
t[0].num = '0'
t[1].num = '1'
t[2].num = '2'
This code will cause errors for indexing t[0], a nil value.
t only has one field and that is t.num
You need to do something like this:
t = {}
for i = 0, 2 do
t[i] = {num = tostring(i)}
end
if you want to create the desired demo table.
As there are many useful functions in Lua that assume 1-based indexing you I'd recommend starting at index 1.
local t = {1,2,3,4,5}
Option 1:
table.remove(t, 1)
Option 2:
t = {table.unpack(t, 2, #t)}
Option 3:
t = table.move(t, 2, #t, 1, t)
t[#t] = nil
Option 4:
for i = 1, #t-1 do
t[i] = t[i+1]
end
t[#t] = nil
There are more options. I won't list them all. Some do it in place, some result in new table objects.
As stated in this answer, by creating a new table using the result of table.unpack:
t = {table.unpack(t, 1, #t)}
I have a file with a large table. Need to open it, get certain values and replace other values with the new ones. With this example, Females and Males Classroom a and b must equal Teachers Classroom a and b.
Read as much as I can on IO, but I cannot seem to get this to work correctly. Any help will be greatly appreciated.
--file with sample data to test, original file has 7000+lines
theData =
{
["theSchool"] =
{
["theTeachers"] =
{
["theClassroom"] =
{
["a"] = 001,
["b"] = 002,
},
},
["theFemales"] =
{
["theClassroom"] =
{
["a"] = 005,
["b"] = 010,
},
},
["theMales"] =
{
["theClassroom"] =
{
["a"] = 012,
["b"] = 014,
},
},
},
}
Then the function file looks like this
local file = io.open(filepath,'r')
local newCa = '["a"] = '..theData.theSchool.theTeachers.theClassroom.a
local newCb = '["b"] = '..theData.theSchool.theTeachers.theClassroom.b
local replaceFa = '["a"] = '..tostring(theData.theSchool.theFemales.theClassroom.a)
local replaceFb = '["b"] = '..tostring(theData.theSchool.theFemales.theClassroom.b)
local replaceMa = '["a"] = '..tostring(theData.theSchool.theMales.theClassroom.a)
local replaceMb = '["b"] = '..tostring(theData.theSchool.theMales.theClassroom.b)
file:close()
--Will it work?
print("Original Values:")
print(newCa)
print(newCb)
print(replaceFa)
print(replaceFb)
print(replaceMa)
print(replaceMb)
file = io.open(filepath,'r+')
function lines_from(filepath)
lines = {}
for line in io.lines(filepath) do
lines[#lines + 1] = line
end
return lines
end
local lines = lines_from(filepath)
for k,v in ipairs(lines) do
if v == replaceFa then
file:write(newCa..'\n')
elseif v == replaceFb then
file:write(newCb..'\n')
elseif v == replaceMa then
file:write(newCa..'\n')
elseif v == replaceMb then
file:write(newCb..'\n')
else
file:write(v..'\n')
end
--('[' .. k .. ']', v)
end
--replaceF = {[a] = newCa, [b] = newCb}
--replaceM = {[a] = newCa, [b] = newCb}
--file:write(replaceF)
--file:write(replaceM)
--print(tostring(theData.theSchool.theFemales.theClassroom.a))
file:close()
file = io.open(filepath,'r')
--Did it work?
print("New Values:")
print(theData.theSchool.theTeachers.theClassroom.a)
print(theData.theSchool.theTeachers.theClassroom.b)
print(theData.theSchool.theFemales.theClassroom.a)
print(theData.theSchool.theFemales.theClassroom.b)
print(theData.theSchool.theMales.theClassroom.a)
print(theData.theSchool.theMales.theClassroom.b)```
> I'll remove all the print things after it works.
try this solution, loading the table in one read of the file will be faster, and writing is also better with one command write
--- read
local handle = io.open("data.lua",'rb')
local data = handle:read("*a")
handle:close()
data = data .. "\n return theData"
local t = loadstring(data)()
-- edit
theData.theSchool.theTeachers.theClassroom.a = theData.theSchool.theTeachers.theClassroom.a + 1
-- write
local function concat(t, r)
r = r or {}
for k,v in pairs(t) do
if type(v)=="table" then
r[#r+1] = string.format('\t["%s"]={\n',k )
concat(v, r)
r[#r+1] = "\t},\n"
else
r[#r+1] = string.format('\t\t["%s"]=%03s,\n',k ,v )
end
end
return r
end
local r = concat(t)
local text = "theData = { \n " .. table.concat(r) .. "}"
print(text) -- just control
local handle = io.open("data.lua",'wb')
local data = handle:write(text)
handle:close()
I am working on this exercise in pil4.
Exercise 15.5:
The approach of avoiding constructors when saving tables with cycles is too radical. It is
possible to save the table in a more pleasant format using constructors for the simple case, and to use
assignments later only to fix sharing and loops. Reimplement the function save (Figure 15.3, “Saving
tables with cycles”) using this approach. Add to it all the goodies that you have implemented in the previous
exercises (indentation, record syntax, and list syntax).
I have tried this with the code below, but it seems not to work on the nested table with a string key.
local function basicSerialize(o)
-- number or string
return string.format("%q",o)
end
local function save(name,value,saved,indentation,isArray)
indentation = indentation or 0
saved = saved or {}
local t = type(value)
local space = string.rep(" ",indentation + 2)
local space2 = string.rep(" ",indentation + 4)
if not isArray then io.write(name," = ") end
if t == "number" or t == "string" or t == "boolean" or t == "nil" then
io.write(basicSerialize(value),"\n")
elseif t == "table" then
if saved[value] then
io.write(saved[value],"\n")
else
if #value > 0 then
if indentation > 0 then io.write(space) end
io.write("{\n")
end
local indexes = {}
for i = 1,#value do
if type(value[i]) ~= "table" then
io.write(space2)
io.write(basicSerialize(value[i]))
else
local fname = string.format("%s[%s]",name,i)
save(fname,value[i],saved,indentation + 2,true)
end
io.write(",\n")
indexes[i] = true
end
if #value > 0 then
if indentation > 0 then io.write(space) end
io.write("}\n")
else
io.write("{}\n")
end
saved[value] = name
for k,v in pairs(value) do
if not indexes[k] then
k = basicSerialize(k)
local fname = string.format("%s[%s]",name,k)
save(fname,v,saved,indentation + 2)
io.write("\n")
end
end
end
else
error("cannot save a " .. t)
end
end
local a = { 1,2,3, {"one","Two"} ,5, {4,b = 4,5,6} ,a = "ddd"}
local b = { k = a[4]}
local t = {}
save("a",a,t)
save("b",b,t)
print()
And I got the wrong ouput.
a = {
1,
2,
3,
{
"one",
"Two",
}
,
5,
{
4,
5,
6,
}
a[6]["b"] = 4
,
}
a["a"] = "ddd"
b = {}
b["k"] = a[4]
How could I make the text ' a[6]["b"] = 4 ' jump out of the table constructor?
I am working on a game using love2d and i haven't quite programmed in lua. Not sure on technical wording so i'll post my code and explain what i'm trying to do:
item = {}
item.stat = {}
player.x = 100
player.y = 100
--
item[0].stat.damage = 10
What i'm trying to do is make an inventory system and an item database. I want to be able to make the item database with the code above so i could add an item like so:
item[1].stat.damage = 10
item[1].stat.speed = 10
item[2].stat.damage = 20
item[2].stat.speed = 5
--
player.inventory[0] = item[1]
player.inventory[1] = item[2]
can someone tell me what coding principle this may so i can research it? I basically want to make a matrix that i can access like above while having the convenience of named arrays instead of saying item[1,"damage"] = 10
Edit:
I realise now i can do item.stat.damage[1] = 10 but i have to setup an array for each one, is there an easier way?
Simply use tables:
player = {}
player.x = 100
print(player.x) -- prints 100
Note that player.x is simply syntactic sugar for player["x"], so the following lines are equivalent:
print(player.x) -- prints 100
print(player["x"]) -- also prints 100
With that in mind, you could construct your game data like this for example:
item = {}
item[1] = {}
item[1].stat = {}
item[1].stat.damage = 10
item[1].stat.speed = 10
item[2] = {}
item[2].stat = {}
item[2].stat.damage = 20
item[2].stat.speed = 5
player = {}
player.x = 100
player.y = 100
player.inventory = {}
player.inventory[1] = item[1]
player.inventory[2] = item[2]
print(player.inventory[2].stat.damage) -- prints 20
print(player["inventory"][2]["stat"]["damage"]) -- equivalent, also prints 20
It is probably a good idea to define functions that create items or players and automatically set all the required fields.
Eventually, you may want to use actual classes and objects (for example, if you want to define methods on your objects).
EDIT:
Here is the example from above with functions create_item, create_player to create items or players. I've used named parameters for these functions so one doesn't have to remember the order of the function parameters (note the curly braces when calling the functions).
function create_item(arg)
local item = {}
item.stat = {}
item.stat.damage = arg.damage
item.stat.speed = arg.speed
return item
end
function create_player(arg)
local player = {}
player.x = arg.x
player.y = arg.y
player.inventory = {}
return player
end
item = {}
item[1] = create_item{damage=10, speed=10}
item[2] = create_item{damage=20, speed=5}
player = create_player{x=100, y=100}
player.inventory[1] = item[1]
player.inventory[2] = item[2]
print(player.inventory[2].stat.damage) -- prints 20
print(player["inventory"][2]["stat"]["damage"]) -- equivalent, also prints 20
You can always shorten your code:
item = {
stat = {},
[0] = { stat = { damage = 10 } },
[1] = { stat = { damage = 10, speed = 10 } },
[2] = { stat = { damage = 20, speed = 5 } },
}
player = { x = 100, y = 100, inventory = { [0] = item[1], [1] = item[2] } }
You can access that code in matrix way like
function item:getstat(index, param)
return self[index] and self[index].stat and self[index].stat[param];
end
function item:setstat(index, param, value)
local t1 = self[index]
if (t1 == nil) then
t1 = {}
self[index] = t1
end
local t2 = t1.stat
if (t2 == nil) then
t2 = {}
t1.stat = t2
end
t2[param] = value
end
print(item:getstat(0, "damage"))
item:setstat(1, "speed", 20)
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
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.
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
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