I have the following string:
mystring = "a=test;b=12345"
I would like to know how to initialize a table in one shot, assign it the value of the string. The string originates from another external application, and if possible I want to avoid having to split it up. Something like this:
mytable = {mystring:gsub(";",",")}
Is it possible to do something like this? I know how to do it in multiple steps... but just wondering if it's possible to do it all at once.
Here's what I've tried and the respective output:
> mystring = "a=123;b=2345"
> myarray = {mystring:gsub(";",",")}
> for key,value in pairs(myarray) do print(key,value) end
1 a=123,b=2345
2 1
>
whereas I was hoping to end up with an array / table where like this:
key value
a 123
b 2345
-- Lua 5.2+ required
function string_to_table (str)
local result = {}
load(str, '', 't', setmetatable({}, {
__index = function(t,k) return k end,
__newindex = result
}))()
return result
end
mytable = string_to_table("a=test;b=12345;c=a") -- {a="test", b=12345, c="a"}
Try this, which lets Lua do the hard work:
function parse(s)
local t={}
load(s,"",nil,t)()
return t
end
mytable=parse("a=123;b=2345")
for k,v in pairs(mytable) do print(k,v) end
Note that this executes the code in the given string, which may be dangerous if it comes from an untrusted source. On the other hand, the damage is limited because the code is executed in an empty environment and so cannot affect existing variables. Malicious code may contain infinite loops or consume all memory, though.
mytable = {}
for key, value in string.gmatch("a=123;b=456", "(%w+)=(%w+)") do
mytable[key] = value
end
print(mytable.a, mytable.b)
Returns:
123
456
as expected. This only works, of course, with alphanumeric and no punctuation.
Related
I have gone through many questions and Google results but couldn't find the solution.
I am trying to sort a table using table.sort function in Lua but I can't figure out how to use it.
I have a table that has keys as random numeric values. I want to sort them in ascending order. I have gone through the Lua wiki page also but table.sort only works with the table values.
t = { [223]="asd", [23]="fgh", [543]="hjk", [7]="qwe" }
I want it like:
t = { [7]="qwe", [23]="fgh", [223]="asd", [543]="hjk" }
You cannot set the order in which the elements are retrieved from the hash (which is what your table is) using pairs. You need to get the keys from that table, sort the keys as its own table, and then use those sorted keys to retrieve the values from your original table:
local t = { [223]="asd", [23]="fgh", [543]="hjk", [7]="qwe" }
local tkeys = {}
-- populate the table that holds the keys
for k in pairs(t) do table.insert(tkeys, k) end
-- sort the keys
table.sort(tkeys)
-- use the keys to retrieve the values in the sorted order
for _, k in ipairs(tkeys) do print(k, t[k]) end
This will print
7 qwe
23 fgh
223 asd
543 hjk
Another option would be to provide your own iterator instead of pairs to iterate the table in the order you need, but the sorting of the keys may be simple enough for your needs.
What was said by #lhf is true, your lua table holds its contents in whatever order the implementation finds feasible. However, if you want to print (or iterate over it) in a sorted manner, it is possible (so you can compare it element by element). To achieve this, you can do it in the following way
for key, value in orderedPairs(mytable) do
print(string.format("%s:%s", key, value))
end
Unfortunately, orderedPairs is not provided as a part of lua, you can copy the implementation from here though.
The Lua sort docs provide a good solution
local function pairsByKeys (t, f)
local a = {}
for n in pairs(t) do table.insert(a, n) end
table.sort(a, f)
local i = 0 -- iterator variable
local iter = function () -- iterator function
i = i + 1
if a[i] == nil then return nil
else return a[i], t[a[i]]
end
end
return iter
end
Then you traverse the sorted structure
local t = { b=1, a=2, z=55, c=0, qa=53, x=8, d=7 }
for key,value in pairsByKeys(t) do
print(" " .. tostring(key) .. "=" .. tostring(value))
end
There is no notion of order in Lua tables: they are just sets of key-value pairs.
The two tables below have exactly the same contents because they contain exactly the same pairs:
t = { [223] = "asd" ,[23] = "fgh",[543]="hjk",[7]="qwe"}
t = {[7]="qwe",[23] = "fgh",[223] = "asd" ,[543]="hjk"}
I would like to contruct a configuration file with the code :
But, my code is wrong, why ? the final line only print nil, nil, nil...
-- Define ten network interfaces
interfaces = {} -- Define an empty table
for n = 1, 10 do
interfaces[n] = {
device = "eth"..n,
address = "192.168.1."..n
}
end
for k, v in pairs(interfaces) do print(device,address) end
In the code below, the names device and address are resolved as global variables that are undefined. Hence the nils in the output.
for k, v in pairs(interfaces) do print(device,address) end
Try this instead:
for k, v in pairs(interfaces) do print(v.device,v.address) end
Since the order of pairs traversed by pairs is not defined, use ipairs if you need the list to be output in order.
I want to know how to get the table hex id. I know that doing:
local some_var = {}
print (some_var)
the result is (for instance):
table: 0x21581c0
I want the hex without the table: string. I know that maybe some of you suggest me to make a regular expression (or something similar) to remove those chars, but I want to avoid that, and just get the 0x21581c0
Thanks
This is simpler and works for all types that are associated with pointers:
local function getId(t)
return string.format("%p", t)
end
print("string:", getId("hi"))
print("table:", getId({}))
print("userdata:", getId(io.stdin))
print("function:", getId(print))
print("number:", getId(1))
print("boolean:", getId(false))
print("nil:", getId(nil))
Result:
string: 0x0109f04638
table: 0x0109f0a270
userdata: 0x01098076c8
function: 0x0109806018
number: NULL
boolean: NULL
nil: NULL
In the standard implementation, there is the global 'print' variable that refers to a standard function that calls, through the global variable 'tostring', a standard function described here. The stanard 'tostring' function is the only way to retrieve the hexadecimal number it shows for a table.
Unfortunately, there is no configuration for either of the functions to do anything differently for all tables.
Nonetheless, there are several points for modification. You can create you own function and call that every time instead, or point either of the the global variables print or tostring to you own functions. Or, set a __tostring metamethod on each table you need tostring to return a different answer for. The advantage to this is it gets you the format you want with only one setup step. The disadvantage is that you have to set up each table.
local function simplifyTableToString(t)
local answer = tostring(t):gsub("table: ", "", 1)
local mt = getmetatable(t)
if not mt then
mt = {}
setmetatable(t, mt)
end
mt.__tostring = function() return answer end
end
local a = {}
local b = {}
print(a, b)
simplifyTableToString(a)
print(a, b)
Without complex patterns, you can just search for the first space, and grab the substring of what follows.
function get_mem_addr (object)
local str = tostring(object)
return str:sub(str:find(' ') + 1)
end
print(get_mem_addr({})) -- 0x109638
print(get_mem_addr(function () end)) -- 0x108cf8
This function will work with tables and functions, but expect errors if you pass it anything else.
Or you can use a little type checking:
function get_mem_addr (o)
return tostring(o):sub(type(o):len() + 3)
end
The table id stated by the OP is invalid in the version of Lua I am using (5.1 in Roblox). A valid ID is length 8, not 9 as in your example. Either way, just use string.sub to get the sub-string you are after.
string.sub(tostring({}), 8)
The reason is, 'table: ' is 7 characters long, so we take from index 8 through the end of the string which returns the hex value.
How can we use lua scripting to implement multi-get.
Let's say if I've set name_last to Beckham and name_first to David. What should the lua script be in order to get both name_last and name_first in one go?
I can implement something like:
eval "return redis.call('get',KEYS[1])" 1 foo
to get the value of single key. Just wondering on how to enhance that scripting part to get values related to all keys (or multiple keys) by just making one call to redis server.
First, you want to send the fields you want to return to EVAL (the 0 indicates that there are no KEYS so these arguments will be accessible from ARGV):
eval "..." 0 name_last name_first
Second, you can query the values for the individual fields using MGET:
local values = redis.call('MGET', unpack(ARGV))
Third, you can maps the values back to the field names (the index of each value corresponds to the same field):
local results = {}
for i, key in ipairs(ARGV) do
results[key] = values[i]
end
return results
The command you'll end up executing would be:
eval "local values = redis.call('MGET', unpack(ARGV)); local results = {}; for i, key in ipairs(ARGV) do results[key] = values[i] end; return results" 0 name_last name_first
Do a loop over the KEYS table and for each store its GET response in a take that you return. Untested code:
local t = {}
for _, k in pairs(KEYS) do
t[#t+1] = redis.call('GET', k)
end
return t
P.S. You can also use MGET instead btw :)
I'm trying to make an __index function in my table which can process ALL of the field it receives.. What I want to do is that if I call the table in the following way
mytable.str1.str2.str3
I should be able to return the table
{"str1", "str2", "str3"}
Note that str1,str2,str3 are undefined, they are just strings. I am not trying to create subtables str1, str2, I just want __index to see everything beyond the first period.
Unfortunately what I have seems that __index only captures str1, and complains that "attempt to index field 'str1' (a nil value)"
Anyone know how this can be done?
I'm not sure why you'd want to do this, but here's how you do it. The comments explain the trick, but basically you need a second metatable to handle the table that's returned from the first call to the __index metamethod.
If this isn't clear, let me know and I can explain in more detail.
-- This metatable appends the new key to itself, then returns itself
stringtablemeta = {}
function stringtablemeta.__index(self, key)
table.insert(self, key)
return self
end
-- In response to the question in the comments:
function stringtablemeta.__tostring(self)
local str = ""
for i, v in ipairs(self) do
if i > 1 then str = str .. "-" end
str = str .. v
end
return str
end
-- This metatable creates a new table, with stringmetatable as its metatable
mytablemeta = {}
function mytablemeta.__index(self, key)
local temp = { key }
setmetatable(temp, stringtablemeta)
return temp
end
-- set mytable to have mymetatable as it's metatable. This makes it so when
-- you index into it, it will call the mytablemeta.__index method.
--
-- That will return a talb with a single string, the key that was passed
-- in. that table will have it's own metatable, the stringmetatable, which
-- will cause it to append keys that are called on it with its own __index
-- metamethod
mytable = {}
setmetatable(mytable, mytablemeta)
test = mytable.str1.str2.str3
for k, v in pairs(test) do
print(k, v)
end
It can't. Not without having a metatable on each of those tables.
mytable is a table. str1 is a different table. So you can do the same thing by doing this:
local temp = mytable.str1
temp.str2.str3
And as far as Lua is concerned, these are equivalent. Therefore, the only way to know what was done at each stage is to give all of them a special metatable. How you concatenate the different values into a table is something you'll have to investigate on your own.
As Nicol said, you cannot do that directly in Lua. However, by returning specially crafted tables, you can achieve a similar result to what you want. Take a look at AutomagicTables at the Lua-users Wiki for inspiration.