Given
local t1 = {
["foo"] = "val1",
["bar"] = "val2",
["baz"] = "val3",
}
local t2 = {
["foo1"] = "val4",
["bar1"] = "val5",
["baz1"] = "val6",
}
Id like to get result
local t3 = {
["foo"] = "val1",
["bar"] = "val2",
["baz"] = "val3",
["foo1"] = "val4",
["bar1"] = "val5",
["baz1"] = "val6",
}
I have been attempting various ways for around a day now, using other questions provided here, and still am unsure of where things are going wrong or how to handle it. The tables vs arrays in lua is a bit hard to grasp. Thanks for any help :D
AFAIK, if the hash part of a table is used, it does not preserve the order. There is a very simple way to highlight this.
t1 = {
["foo"] = "val1",
["bar"] = "val2",
["baz"] = "val3",
}
for k,v in pairs(t1) do
print(k, v)
end
On my computer, the order is not preserved:
foo val1
baz val3
bar val2
If the order is important, it is required to use an array.
One (convoluted) way to do it would be the following code. Obviously, I am not aware of the given requirements, so this code might not be the most straight-forward.
t1 = {
{ foo = "val1" }, -- Element t1[1]
{ bar = "val2" }, -- Element t1[2]
{ baz = "val3" } -- Element t1[3]
}
t2 = {
{ foo1 = "val4" }, -- Element t2[1]
{ bar1 = "val5" }, -- Element t2[2]
{ baz1 = "val6" } -- Element t2[3]
}
function merge (t1, t2)
local new_table = {}
-- Copy all the items from the first table
for index = 1, #t1 do
new_table[#new_table+1] = t1[index]
end
-- Copy all the items from the second table
for index = 1, #t2 do
new_table[#new_table+1] = t2[index]
end
-- return the new table
return new_table
end
for k,v in pairs(merge(t1,t2)) do
local subtable = v
for k,v in pairs(subtable) do
print(k,v)
end
end
This would print the following:
foo val1
bar val2
baz val3
foo1 val4
bar1 val5
baz1 val6
Related
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.
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?
Is there a way to implement a mechanism similar to python's __getitem__?
for instance, having the following:
local t1 = {a=1, b=2, c=3, d=4}
if in code, t1.e will be called, then I wish to have something else returned rather than nil
You can use setmetatable and the __index metamethod:
local t1 = {a = 1, b = 2, c = 3, d = 4}
setmetatable(t1, {
__index = function(table, key)
return "something"
end
})
print(t1.hi) -- prints "something"
Note that this will not be called when you do t.nonexistant = something. For that, you need the __newindex metamethod:
local t1 = {a = 1, b = 2, c = 3, d = 4}
setmetatable(t1, {
__index = function(table, key)
return "something"
end,
__newindex = function(table, key, value)
rawset(table, tostring(key) .. '_nope', value)
end
})
print(t1.hi) -- prints "something"
t1.hi = 'asdf'
print(t1.hi) -- prints "something"
print(t1.hi_nope) -- prints "asdf"
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