I have a table A that contain the following
for i,v in pairs(Table A) do print (i,v) end
1 a
2 table : 50382A03 -- table B
3 hi
. Is there a way that I can get the table B value to be print out while I m printing the parent table A, or i can store it and print it again using the same function?.
thanks
Jp
When the question contains "nested", the answer will probably contain recursion:
function printTable(t)
function printTableHelper(t, spacing)
for k,v in pairs(t) do
print(spacing..tostring(k), v)
if (type(v) == "table") then
printTableHelper(v, spacing.."\t")
end
end
end
printTableHelper(t, "");
end
Just beware of circular references.
A bit changed function for better output and abstraction:
function printTableHelper(t,spacing)
local spacing = spacing or ''
if type(t)~='table' then
print(spacing..tostring(t))
else
for k,v in pairs(t) do
print(spacing..tostring(k),v)
if type(v)=='table' then
printTableHelper(v,spacing..'\t')
end
end
end
end
printTableHelper({'a',{'b'},'c'})
Just head on to the lua-users wiki page on table serialization and choose your champion. For example the following code handles everything including cycles in tables (local a={}; a.t = a):
-- alt version2, handles cycles, functions, booleans, etc
-- - abuse to http://richard.warburton.it
-- output almost identical to print(table.show(t)) below.
function print_r (t, name, indent)
local tableList = {}
function table_r (t, name, indent, full)
local serial=string.len(full) == 0 and name
or type(name)~="number" and '["'..tostring(name)..'"]' or '['..name..']'
io.write(indent,serial,' = ')
if type(t) == "table" then
if tableList[t] ~= nil then io.write('{}; -- ',tableList[t],' (self reference)\n')
else
tableList[t]=full..serial
if next(t) then -- Table not empty
io.write('{\n')
for key,value in pairs(t) do table_r(value,key,indent..'\t',full..serial) end
io.write(indent,'};\n')
else io.write('{};\n') end
end
else io.write(type(t)~="number" and type(t)~="boolean" and '"'..tostring(t)..'"'
or tostring(t),';\n') end
end
table_r(t,name or '__unnamed__',indent or '','')
end
Related
I have a nested array, for example,
someTable = {"value1", "value2", {"value3a", "value3b", {"value4a", "value4b", "value4c"}}
and trying to find a way to get all of these different elements at different hierarchies to actually come down to a single hierarchy
expected results,
newTable = {"value1", "value2", "value3a", "value3b", "value4a", "value4b", "value4c"}
I've found this below code that actually prints all those elements, but I couldn't find a way to make it into a new table with one hierarchy an return it
function DeepPrint (e)
-- if e is a table, we should iterate over its elements
if type(e) == "table" then
for k,v in pairs(e) do -- for every element in the table
print(k)
DeepPrint(v) -- recursively repeat the same procedure
end
else -- if not, we can just print it
print(e)
end
end
I agree with what Doj is saying, but you don't need two functions to do that.
Just recursively call initial function, like you did with your print example above.
#! /usr/bin/env lua
someTable = {"value1", "value2", {"value3a", "value3b", {"value4a", "value4b", "value4c"}}}
function flatten( item, result )
local result = result or {} -- create empty table, if none given during initialization
if type( item ) == 'table' then
for k, v in pairs( item ) do
flatten( v, result )
end
else
result[ #result +1 ] = item
end
return result
end
newTable = flatten( someTable )
for i = 1, #newTable do print( newTable[i] ) end
Instead of printing the elements just insert them to result table:
function flattenRecursive(e, result)
-- if e is a table, we should iterate over its elements
if type(e) == "table" then
for k,v in pairs(e) do -- for every element in the table
flattenRecursive(v, result) -- recursively repeat the same procedure
end
else -- if not, we can just put it to the result
table.insert(result, e)
end
end
function flatten (e)
local result = {}
flattenRecursive(e, result)
return result
end
Test:
example = {"value1", "value2", {"value3a", "value3b", {"value4a", "value4b", "value4c"}}}
example_result = flatten(example)
for k,v in pairs(example_result) do
print(v)
end
I am currently learning Lua, and I am attempting to create a bubble sort algorithm with it. However, I am unable to get this to work. Is anyone able to point out why?
Some details I can point out are that, on shorter lists such as lists 3 elements long, the algorithm does succeed in sorting it but then continues to sort it as if it was not sorted. On longer lists such as lists 5 elements long, the program does not sort it at all. I have gotten this information by making the program print the list every time two elements are swapped.
user_input = 0
list = {}
while user_input ~= "SORT" do
print("Input number value, or input SORT to start sort")
user_input = io.read()
if user_input ~= "SORT" then
table.insert(list, user_input)
end
end
done = false
while done == false do
done = true
for k, v in pairs(list) do
if k ~= 1 then
if list[k] < list[k - 1] then
list[k], list[k - 1] = list[k - 1], list[k]
done = false
for k, v in pairs(list) do
io.write(v .. " ")
end
print()
end
end
if k == 1 then
if list[k] < list[table.maxn(list)] then
list[k], list[table.maxn(list)] = list[table.maxn(list)], list[k]
done = false
for k, v in pairs(list) do
io.write(v .. " ")
end
print()
end
end
end
end
io.write("RESULT: ")
for k, v in pairs(list) do
io.write(v .. " ")
end
print()
In Lua there are 2 functions for creating iterators for tables pairs and ipairs
With pairs the order produced is indeterminate, it will returned all key, value pairs but the order can not be garenteed.
You can find this under next in the reference manual for Lua 5.1
example: {1,2,3,4,5} the output could be 5,2,4,1,3
the order of ipairs is 1 to the first nil it will not return any non-integer keys.
example: {1,2,3,nil,5} would give you 1,2,3
Using pairs your algorithm's output could be correct but could appear incorrect due to the ordering from pairs
You want you use ipairs to evaluate your algorithm's output, so that it will be ordered by index.
Your algorithm does not perform a bubble sort as it is now, I can include corrections for that if you want. For this initial answer I think clearing up what would create an inconsistent output should point you in the right direction.
A bubble sort should "sort" 1 index at a time, the first pass will get the last value of the array sorted. then each pass after sorts following position. for example:
before first pass 2,1,3,4,5,8,7,6
after first pass 1,2,3,4,5,7,6,8
Wikipedia has great pages for sorting algorithms with gif images that can really help understand how it should function: Bubble Sort
You're using pairs() instead of ipairs()
plus your code has an extra maxn() routine that isn't needed.
#! /usr/bin/env lua
local user_input = 0
local list = {}
while user_input ~= 'sort' do
print( 'Input number value, or input SORT to start sort' )
user_input = io.read() :lower()
-- the word 'sort' doesn't return a number, thus no final insertion
table.insert( list, tonumber( user_input ) )
end
local found_swap = true
while found_swap do
found_swap = false
for i = 2, #list do
if list[i] < list[i -1] then
list[i], list[i -1] = list[i -1], list[i]
found_swap = true
end
end
end
io.write( 'RESULT: ' )
for i, v in ipairs( list ) do
io.write( v ..' ' )
end
print()
here's my implementation, a couple notes:
My version of lua (luau) supports type checking etc. so you may need to remove : table from the paramater. (If you'd like to find more out about luau - here's the link: https://roblox.github.io/luau/ - it's really cool)
local function bubbleSort(t: table)
local function check(i, v)
local nextNum = t[i+1]
if nextNum and (nextNum < v) then
t[i] = nextNum
t[i + 1] = v
return true
end
end
local changeMade
repeat
changeMade = false
for i, v in next, t do
changeMade = check(i, v) or changeMade
end
until changeMade == false
end
local tableForSorting = {2,5,4} --2,4,5
bubbleSort(tableForSorting)
print(tableForSorting)
Hope this is of some help and shows how you can really slim down your codebase and it still work exactly the same! The reason yours wasn't working - as others - have mentioned is pairs() doesn't consistently order the list the same way.
In practise we use pairs() for dictionaries while we use ipairs() for arrays. You'll notice i'm using next in this example, next is exactly the same as ipairs(). Drop a question below if you have any follow up questions :)!
In my Lua project I receive an array, encode it into JSON and pass further. My Lua encode function looks like the following:
local function encode_table(val, stack)
local res = {}
stack = stack or {}
-- Circular reference?
if stack[val] then error("circular reference") end
stack[val] = true
if val[1] ~= nil or next(val) == nil then
-- Treat as array -- check keys are valid and it is not sparse
local n = 0
for k in pairs(val) do
if type(k) ~= "number" then
error("invalid table: mixed or invalid key types")
end
n = n + 1
end
-- need to add a stub somewhere here above the next line
if n ~= #val then
error("invalid table: sparse array") -- THIS TRIGGERS and stops the code
end
-- Encode
for i, v in ipairs(val) do
table.insert(res, encode(v, stack))
end
stack[val] = nil
return "[" .. table.concat(res, ",") .. "]"
else
-- Treat as an object
for k, v in pairs(val) do
if type(k) ~= "string" then
error("invalid table: mixed or invalid key types")
end
table.insert(res, encode(k, stack) .. ":" .. encode(v, stack))
end
stack[val] = nil
return "{" .. table.concat(res, ",") .. "}"
end
end
The problem is that I reveive an array with a 1 element missing. I need to add a stub for it in a key - value manner, say
myArray['missingKey'] = 'somestubvalue'
but I donk know how to do that. Also there is a check in the code for sparse array and this check throws an error, so I need to add a stub before this check is done (pls see the code). Any ideas how to do that would be welcome. Thank you.
I wrote the following function: deleteStrings .
That gets as input map of words and their length (mapWords),
and list of words.(listWords)
I want to remove from the map, keys that don't exist in the list.
I'm getting "lua error".
function deleteStrings(mapWords,listWords)
local CleanedMap = mapWords
for key in map.keys(mapWords) do
if not contains(listWords,key) then
CleanedMap=map.remove(CleanedMap,key)
end
end
end
function contains(list, word)
for _, v in pairs(list) do
if v == word then return true end
end
return false
end
What is wrong with this code?
Thanks
I'm trying, as an exercise, to make a set implementation in Lua. Specifically I want to take the simplistic set implementation of Pil2 11.5 and grow it up to include the ability to insert values, delete values, etc.
Now the obvious way to do this (and the way that works) is this:
Set = {}
function Set.new(l)
local s = {}
for _, v in ipairs(l) do
s[v] = true
end
return s
end
function Set.insert(s, v)
s[v] = true
end
ts = Set.new {1,2,3,4,5}
Set.insert(ts, 5)
Set.insert(ts, 6)
for k in pairs(ts) do
print(k)
end
As expected I get the numbers 1 through 6 printed out. But those calls to Set.insert(s, value) are really rather ugly. I'd much rather be able to call something like ts:insert(value).
My first attempt at a solution to this looked like this:
Set = {}
function Set.new(l)
local s = {
insert = function(t, v)
t[v] = true
end
}
for _, v in ipairs(l) do
s[v] = true
end
return s
end
ts = Set.new {1,2,3,4,5}
ts:insert(5)
ts:insert(6)
for k in pairs(ts) do
print(k)
end
This works mostly fine until you see what comes out of it:
1
2
3
4
5
6
insert
Very obviously the insert function, which is a member of the set table, is being displayed. Not only is this even uglier than the original Set.insert(s, v) problem, it's also prone to some serious trouble (like what happens if "insert" is a valid key someone is trying to enter?). It's time to hit the books again. What happens if I try this instead?:
Set = {}
function Set.new(l)
local s = {}
setmetatable(s, {__call = Set.call})
for _, v in ipairs(l) do
s[v] = true
end
return s
end
function Set.call(f)
return Set[f]
end
function Set.insert(t, v)
t[v] = true
end
ts = Set.new {1,2,3,4,5}
ts:insert(5)
ts:insert(6)
for k in pairs(ts) do
print(k)
end
Now the way I'm reading this code is:
When I call ts:insert(5), the fact that insert doesn't exist to be called means that the ts metatable is going to be searched for "__call".
The ts metatable's "__call" key returns Set.call.
Now Set.call is called with the name insert which causes it to return the Set.insert function.
Set.insert(ts, 5) is called.
What's really happening is this:
lua: xasm.lua:26: attempt to call method 'insert' (a nil value)
stack traceback:
xasm.lua:26: in main chunk
[C]: ?
And at this point I'm stumped. I have absolutely no idea where to go from here. I hacked around for an hour with varying degrees of increasingly desperate variations on this code but the end result is that I have nothing that works. What undoubtedly obvious thing am I overlooking at this point?
Now the way I'm reading this code is:
When I call ts:insert(5), the fact that insert doesn't exist to be called means that the ts metatable is going to be searched for "__call".
There's your problem. The __call metamethod is consulted when the table itself is called (ie, as a function):
local ts = {}
local mt = {}
function mt.__call(...)
print("Table called!", ...)
end
setmetatable(ts, mt)
ts() --> prints "Table called!"
ts(5) --> prints "Table called!" and 5
ts"String construct-call" --> prints "Table called!" and "String construct-call"
Object-oriented colon-calls in Lua such as this:
ts:insert(5)
are merely syntactic sugar for
ts.insert(ts,5)
which is itself syntactic sugar for
ts["insert"](ts,5)
As such, the action that is being taken on ts is not a call, but an index (the result of ts["insert"] being what is called), which is governed by the __index metamethod.
The __index metamethod can be a table for the simple case where you want indexing to "fall back" to another table (note that it is the value of the __index key in the metatable that gets indexed and not the metatable itself):
local fallback = {example = 5}
local mt = {__index = fallback}
local ts = setmetatable({}, mt)
print(ts.example) --> prints 5
The __index metamethod as a function works similarly to the signature you expected with Set.call, except that it passes the table being indexed before the key:
local ff = {}
local mt = {}
function ff.example(...)
print("Example called!",...)
end
function mt.__index(s,k)
print("Indexing table named:", s.name)
return ff[k]
end
local ts = {name = "Bob"}
setmetatable(ts, mt)
ts.example(5) --> prints "Indexing table named:" and "Bob",
--> then on the next line "Example called!" and 5
For more information on metatables, consult the manual.
You said:
Now the way I'm reading this code is:
When I call ts:insert(5), the fact that insert doesn't
exist to be called means that the ts metatable is going
to be searched for "__call".
The ts metatable's "__call" key returns Set.call.
Now Set.call is called with the name insert which causes
it to return the Set.insert function.
Set.insert(ts, 5) is called.
No, what happens is this:
When insert isn't found directly in the ts object, Lua looks for __index in its metatable.
If it is there and it is a table, Lua will search for insert there.
If it is there and it is a function, it will call it with the original table (ts in this case) and the key being searched for (insert).
If it isn't there, which is the case, it is considered nil.
The error you're having is because you don't have __index set in your metatable, so you are effectively calling a nil value.
This can be solved by pointing __index to some table, namely Set, if you're going to store your methods there.
As for __call, it is used for when you call the object as a function. Ie:
Set = {}
function Set.new(l)
local s = {}
setmetatable(s, {__index=Set, __call=Set.call})
for _, v in ipairs(l) do
s[v] = true
end
return s
end
function Set.call(s, f)
-- Calls a function for every element in the set
for k in pairs(s) do
f(k)
end
end
function Set.insert(t, v)
t[v] = true
end
ts = Set.new {1,2,3,4,5}
ts:insert(5)
ts:insert(6)
ts(print) -- Calls getmetatable(ts).__call(ts, print),
-- which means Set.call(ts, print)
-- The way __call and __index are set,
-- this is equivalent to the line above
ts:call(print)
Set = {}
function Set.new(l)
local s = {}
setmetatable(s, {__index=Set})
for _, v in ipairs(l) do
s[v] = true
end
return s
end
function Set.call(f)
return Set[f]
end
function Set.insert(t, v)
t[v] = true
end
ts = Set.new {1,2,3,4,5}
ts:insert(5)
ts:insert(6)
for k in pairs(ts) do
print(k)
end
I modified your first version and this version would offer the features I think you are looking for.
Set = {}
Set.__index = Set
function Set:new(collection)
local o = {}
for _, v in ipairs(collection) do
o[v] = true
end
setmetatable(o, self)
return o
end
function Set:insert(v)
self[v] = true
end
set = Set:new({1,2,3,4,5})
print(set[1]) --> true
print(set[10]) --> nil
set:insert(10)
print(set[10]) --> true