What am I looking for is a code like that.
local sometable = {
[1] = [2] = "abc",
}
So this is surely a wrong way to set 2 keys. ( returned an error )
You received an error because Lua doesn't have a syntax for setting multiple keys to a single value in a table constructor.
You have a few options, when using tables as arrays (sequences) you can omit the key:
local t = {'abc', 'abc'}
If you don't want to repeat the value, use a variable:
local init = 'abc'
local t = {init, init}
Or, write a function to do the initialization:
local function initialize(t, v, first, last)
first = first or 1
last = last or first
assert(first <= last, 'invalid first/last')
for i = first, last do
t[i] = v
end
return t
end
local t = initialize({}, 'abc', 1, 2)
Related
If I have a given dictionary how would I make the key name into the name of a variable and assign the keys value to that variable. For example if I have the dictionary num = {num1 = 1, num2 = 2, num3 = 3}, I want to be able to have the variable num1 = 1 , num2 = 2 and num3 = 3. This is an example dictionary but I need this for a particular function where the number of items in the dictionary is unknown and the elements of the dictionary are also unknown. What I've tried so far is:
local num = {num1 = 1, num2 = 2, num3 = 3}
local keys = {}
local values = {}
for name,value in pairs(num) do
table.insert(keys,name)
table.insert(values,value)
end
for i,v in pairs(keys) do
print(v,values[i])
end
The last for loop is pretty much there just to show how I wanted to access each key, value pair but I don't know how I would go about making them into the form variable = value were the variable is available globally.
You cannot convert table items into variables. Your best bet is to either manually create the variables or read off the table
print(nums.num1) -- returns 1
As you can tell I'm a beginner in lua. I am trying to understand a function I'm stuck at what the following code segment does?
It is used in the following code snippet in the last line:
function classify(txt_dir, img_dir, cls_list)
local acc = 0.0
local total = 0.0
local fea_img = {}
local fea_txt = {}
for fname in io.lines(cls_list) do
local imgpath = img_dir .. '/' .. fname .. '.t7'
local txtpath = txt_dir .. '/' .. fname .. '.t7'
fea_img[#fea_img + 1] = extract_img(imgpath)
fea_txt[#fea_txt + 1] = extract_txt(txtpath)
end
for i = 1,#fea_img do
-- loop over individual images.
for k = 1,fea_img[i]:size(1) do
local best_match = 1
local best_score = -math.huge
for j = 1,#fea_txt do
local cur_score = torch.dot(fea_img[i][{k,{}}], fea_txt[j])
From my understanding, fea_img is a lua table. Is the line fea_img[i][{k,{}}] some sort of slicing for the value for the key 'i' in the table fea_img?
I tried searching for more examples and found this being used here too (last line):
for i = 1,nsamples,batchsize do
-- indices
local lasti = math.min(i+batchsize-1,nsamples)
local m = lasti - i + 1
-- k-means step, on minibatch
local batch = x[{ {i,lasti},{} }]
Any help on this would be really appreciated. Thank you!
In lua you can access a specific index on a table in multiple ways. Like these two examples
local myValue = someTable.theIndex
-- or
local myOtherValue = someTable[2]
So the construct you see here is to access some values from a (nested) table.
Also in lua you can use anything except nil as a index, so even tables are possible.
The line
fea_img[i][{k,{}}]
Can be extended to this:
local index1 = i -- i in this case is your loop variable
local index2 = { k , { } } -- This creates a table with 2 values, the first one will be the vaule of the var k, the second one is an empty table
local value1 = fea_img[index1] -- This will get you a table
local value2 = value1[index2] -- This will get the same as: fea_img[i][{k,{}}]
Correction and Addition:
As Nicol Bolas already said in the comments: The index must be an exact match. Which means it literally has to be the same table, which is not the case for the presented code from you. Either you dropped code you thought is unnecessary or fea_img has some some kind of metatable on it.
In the case of
local k = 2
local table1 = {k, { } }
local table2 = {k, { } }
table2 and table1 do have the exact same content. But they are not the same table. Which will lead to nil always being retrieved if one is used to store data in a table and the other is used to get it back.
Syntactically, t[k] is indexing a table with a key. Normally, if there is a record in the table with the key k, its value is returned. Nothing more, nothing less.
If fea_img[i] was a normal table, {k,{}} would always return nil, since table indices are resolved based on their identity ({k,{}} is always a new table). Based on your code, I have to conclude that the elements of fea_img (i.e. what extract_img returns) are not normal tables.
In Lua, you can override the indexing operation using a metatable. If you index a value that has a metatable with __index, it will be used if there is no matching record in the table:
local t = {}
setmetatable(t, {
__index = function(t, k)
return k
end
})
print(t[{}])
This table has a metatable associated with it, which is used in the indexing operation. In this case __index returns the key, but whatever library you are using might provide more complex behaviour.
This is specific to the library you are using, not something related to the Lua syntax.
Why isn't this working? I'm trying to put all my object tables in a single table and use a forloop to iterate through each of them and draw. It shows an error message saying: "}" expected near "=" at line 5
function love.load()
solidstatic = {
ground = {x = 0,y = 160,width = 1000,height = 1000},
box = {x = 80,y = 100,width = 15,height = 15}
}
end
function love.draw()
for i,obj in ipairs(solidstatic) do
love.graphics.rectangle("fill",obj[x],obj[y],obj[width],obj[height])
end
end
(edit) solved the error problem, I was running the wrong .lua file. But still, it doesn't draw anything on the screen
Two things.
Firstly, you must use pairs instead of ipairs to list keys that are not numbers.
for i, v in pairs(table) do
...
end
You must also index the variables as a string.
t = {
x = 1
}
t['x'] = 1
-- or
t.x = 1
This is because doing it without quotes would be indexing with the global variable x, which doesn't exist.
You need to use pairs instead of ipairs to iterate over elements in solidstatic as there are no array keys in that table.
How can I get variables that not declared yet?
Here are simple example:
a = b
b = 123
What I want from these 2 lines is a << 123. But obv it doesn't work.
I know the easy way to get the answer a = 123 is cut 1st line and paste it to lower than 2nd line.
But I'm in some problem. I need some function like 'WillDeclaredVar()' that I can use in like this:
a = WillDeclaredVar(b)
sheepCount = 123
b = sheepCount
print(a)
so I can get the answer '123'.
Or there are any built-in functions that will allows me to do similar thing?
===
I think the link given by timrau is not telling my case. the key point is how to get Variables 'that not declared yet'.
===
Adding actual Code:
triggerCount = 0 -- Counting number of 'Trigger' function
local Trigger = function (t)
triggerCount = triggerCount + 1
return Trigger (t)
end
-- following Triggers are same as while statement.
-- following Triggers doing: Add 1 MarineCount until get 64000 MarineCount
Trigger { -- Here the Trigger function. Now triggerCount = 1.
players = {P1}
actions = {
SetDeaths(P1, Add, 1, "Terran Marine")
},
flag = {preserved},
}
Portal(LoopStart);
-- function Portal(VariableName) returns VariableName = triggerCount. So LoopStart = 1.
Trigger { -- Now triggerCount = 2.
players = {P1}
actions = {
LinkList(LoopEnd, LoopStart);
-- function LinkList(From, To) changes 'From' Trigger's next pointer to the 'To' Trigger.
-- But now the problem happens. Because 'LoopEnd' is not declared yet.
},
flag = {preserved},
}
Trigger { -- Now triggerCount = 3.
players = {P1}
conditions = {
Deaths(P1, Exactly, 64000, "Terran Marine");
}
actions = {
_LinkList(LoopEnd);
-- Reset LoopEnd's next pointer(= LoopEscape) if MarineCount hits 64000
},
flag = {preserved},
}
Portal(LoopEnd); -- LoopEnd = 3.
Changing Order of Triggers will break the Trigger logic(while statement).
All i want is get easy to coding. To put in bluntly, I don't need to solve this problem(get undeclared var). I can imagine a few ways to avoid it. But if i using these ways then the coding work will be very complicated and the difficulty of coding will increases greatly. The difficulty made me stop coding in recent months.
How can I get variables that not declared yet?
Short of time travel, you can't.
Your example code doesn't explain the motivation for the question, because this:
a = WillDeclaredVar(b)
sheepCount = 123
b = sheepCount
print(a)
Can trivially be rearranged into this:
sheepCount = 123
b = sheepCount
a = WillDeclaredVar(b)
print(a)
It would be easier to answer your question if you showed the actual problem you're trying to solve (to avoid an XY problem).
However, as stated there are few things we can note.
First, you need to distinguish between declaring a variable and giving it a value. In Lua you can say:
local b
To declare b as a local variable, which presumably will make a slot for it in the stack frame and let you bind closures to it, before you give it a value. However, the line:
a = WillDeclaredVar(b)
Will pass WillDeclaredVar the value that b currently has, and there's no way for a to change retroactively as a result of b being assigned a new value. That's simply not going to happen, ever. Neither a nor WillDeclaredVar are even aware that b exists, they are receive the value it contains at the point of call.
You could however bind the variable b to a closure which will fetch b's current value when needed.
-- declare b before giving it a value, aka "forward reference"
local b
a = function() return b end
sheepCount = 123
b = sheepCount
print(a()) -- call a to get b's current value
Another way to do that would be to make b a global variable, which is really just a key into your environment table, so you could say:
a = WillDeclaredVar('b')
And have a be some object that can fetch the current value of __ENV['b'] when required.
However, neither of these will support this syntax:
print(a)
a needs to be a function, something that looks up the value of b when needed rather than simply holding a previously computed value. You could do it in this particular instance (i.e. a needs to be convertable to a string), by creating a proxy object that implements __tostring.
function WillDeclaredVar(variableName)
local proxy = { environment = _ENV or _G, variableName = variableName }
return setmetatable(proxy, {
__tostring = function(proxy)
return proxy.environment[proxy.variableName]
end
})
end
-- a will compute a value based on the current value of b when needed
a = WillDeclaredVar('b')
sheepCount = 123
b = sheepCount
print(a)
Output:
123
To make var1 be a reference for var2 write var1 = ReferenceF or var2 (please note a space inside "ReferenceFor"!)
do
local values, references, reference_flag = {}, {}
setmetatable(_G, {
__index = function (_, name)
if name == 'ReferenceF' then
reference_flag = true
elseif reference_flag then
reference_flag = false
return {[references] = name}
elseif references[name] then
return _G[references[name]]
else
return values[name]
end
end,
__newindex = function (_, name, val)
if type(val) == 'table' and val[references] then
references[name] = val[references]
else
values[name] = val
end
end
})
end
a = ReferenceF or b -- a is Reference For b
b = ReferenceF or c -- b is Reference For c
sheepCount = 123
c = sheepCount
print(a, b, c) --> 123 123 123
What I'm currently trying to do is make a table of email addresses (as keys) that hold person_records (as values). Where the person_record holds 6 or so things in it. The problem I'm getting is that when I try to assign the email address as a key to a table it complains and says table index is nil... This is what I have so far:
random_record = split(line, ",")
person_record = {first_name = random_record[1], last_name = random_record[2], email_address = random_record[3], street_address = random_record[4], city = random_record[5], state = random_record[6]}
email_table[person_record.email_address] = person_record
I wrote my own split function that basically takes a line of input and pulls out the 6 comma seperated values and stores them in a table (random_record)
I get an error when I try to say email_table[person_record.email_address] = person_record.
But when I print out person_record.email_address it's NOT nil, it prints out the string I stored in it.. I'm so confused.
function split(str, pat)
local t = {} -- NOTE: use {n = 0} in Lua-5.0
local fpat = "(.-)" .. pat
local last_end = 1
local s, e, cap = str:find(fpat, 1)
while s do
if s ~= 1 or cap ~= "" then
table.insert(t,cap)
end
last_end = e+1
s, e, cap = str:find(fpat, last_end)
end
if last_end <= #str then
cap = str:sub(last_end)
table.insert(t, cap)
end
return t
end
The following code is copy and pasted from your example and runs just fine:
email_table = {}
random_record = {"first", "second", "third"}
person_record = {first_name = random_record[1], last_name = random_record[1], email_address = random_record[1]}
email_table[person_record.email_address] = person_record
So your problem is in your split function.
BTW, Lua doesn't have "hashtables". It simply has "tables" which store key/value pairs. Whether these happen to use hashes or not is an implementation detail.
It looks like you iterating over some lines that have comma-separated data.
Looking at your split function, it stops as soon as there's no more separator (,) symbols in particular line to find. So feeding it anything with less than 3 ,-separated fields (for very common example: an empty line at end of file) will produce a table that doesn't go up to [3]. Addressing any empty table value will return you a nil, so person_record.email_address will be set to nil as well on the 2nd line of your code. Then, when you attempt to use this nil stored in person_record.email_address as an index to email_table in 3rd line, you will get the exact error you've mentioned.