Get all repeated itens from a table in Lua - lua

I need a little help here
Let's suppose I have a table with numbers.
tbl = {'item1' = 6, 'item2' = 1, 'item3' = 6, 'item4' = 3, 'item5' = 2, 'item5' = 3}
I wanna put all repeated numbers in the same table (with key and value) like this:
repeated = {'item1' = 6, 'item3' = 6, 'item4' = 3, 'item5' = 3}
and creat a new one with the "not repeated" numbers:
notrepeated = {'item2' = 1, 'item5' = 2}
Can someone help? Thank you so much.

-- Count the items for each number
local itemsByNum = {}
for item, num in pairs(tbl) do
itemsByNum[num] = (itemsByNum[num] or 0) + 1
end
-- Now move objects to the respective tables
local rep, noRep = {}, {} -- can't use "repeat" as that's a Lua keyword
for item, num in pairs(tbl) do
if itemsByNum[num] > 1 then -- repeated at least once
rep[item] = num
else -- unique number
norep[item] = num
end
end

Related

Check if table contains number

I need to check if a table contains a specific number that is known.
e.g. My variable is {1, 2, 3, 4, 5} and I want to know how I can check if that variable contains the number 3.
Thanks in advance.
Just loop over the values of your table and compare them against the number:
function contains(table, number)
for key, value in pairs(table) do if value == number then return true end end
return false
end
this will search through the values of both hash & list part. Usage based on your example: var = {1, 2, 3, 4, 5}; assert(contains(var, 3)).
If your list is sorted, you can use a binary search:
function contains(t, num)
local upper = #t
local lower = 1
while upper >= lower do
local mid = math.floor((lower + upper) / 2)
local v = t[mid]
if v < num then
lower = mid + 1
elseif v > num then
upper = mid - 1
else -- v == num
return true
end
end
return false
end

How could i loop through every OTHER element in a table in Roblox.lua

I am trying to loop through every other element in an table but I cannot find a way to do so.
Any help is appreciated.
Thank you.
It depends what kind of table you're working with. If you have an array-like table, you can use a simple for-loop :
local t = {1, 2, 3, 4, 5, 6, 7, 8}
-- start at 1, loop until i > the length of t, increment i by 2 every loop
for i = 1, #t, 2 do
local val = t[i]
print(val) -- will print out : 1, 3, 5, 7
end
But if you have a dictionary-like table, you will need something to track which key to skip. You could use a simple boolean to keep track, but be aware that there is no guaranteed order of a dictionary-like table.
local t = {
a = 1,
b = 2,
c = 3,
d = 4,
}
local shouldPrint = true
for k, v in pairs(t) do
-- only print the value when it's true
if shouldPrint then
print(k, v) -- will probably print a, 1 and c, 3
end
-- swap shouldPrint's value every loop
shouldPrint = !shouldPrint
end
Maybe try this
local count = 0
for i = 1 , #table/2 do
table[count + i].value = value
count = count + 1
end
Add to the count as you go down

How to make a table with 100 values but with increasing values?

My professor taught me this (below), for creating a 10 numbers table, but
v = {}
for i = 1, 10 do
v[i] = i
end
print(v[3])
(the output will get me 3, as expected)
why do I recieve "nill" if I try doing this? (bellow)
v = {}
for i = 1, 10, 2 do
v[i] = i
end
print(v[42])
As you can see, I was trying to make a table like this
v = {1,3, 5, 7, 9}
Why it is not working? :(
<3
You're filling only the odd-numbered positions.
Try
for i = 1,5 do
v[i] = 2*i-1
end

How do you do the Fisher-Yates shuffle in Lua

I've been asking questions on random numbers, and I decide the Fisher-Yates shuffle would be the best option. I make a table 't'
t = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}
Now, how would I even shuffle these and be able to use them individually, for example generate the results in another table u
u = {}
For those that find this answer later, this will shuffle in place without making a new table:
local function ShuffleInPlace(t)
for i = #t, 2, -1 do
local j = math.random(i)
t[i], t[j] = t[j], t[i]
end
end
And this one that returns a shuffled table without touching the original (unlike the current answer, which both shuffles in-place and returns a copy):
local function Shuffle(t)
local s = {}
for i = 1, #t do s[i] = t[i] end
for i = #t, 2, -1 do
local j = math.random(i)
s[i], s[j] = s[j], s[i]
end
return s
end
Usage:
local t = {"a", "b", "c", "d", "e", "f"}
print(table.concat(t)) --> abcdef
local s = Shuffle(t)
print(table.concat(t)) --> abcdef (unchanged)
print(table.concat(s)) --> fbcade (shuffled)
ShuffleInPlace(t)
print(table.concat(t)) --> dcbfea (shuffled)
And a quick sanity check that they're uniform:
local t = {"a", "b", "c"}
local results = {abc = 0,acb = 0,bac = 0,bca = 0,cab = 0,cba = 0}
for i = 1, 10000000 do
ShuffleInPlace(t)
local r = table.concat(t)
results[r] = results[r] + 1
end
for k, v in pairs(results) do print(k, v) end
--[[
cba 1667473
cab 1666235
bca 1665672
bac 1666782
acb 1666447
abc 1667391
--]]
NOTE: Check the other answer https://stackoverflow.com/a/68486276/1190388 which fixes an issue in the code snippet below as well as providing other alternatives
If you do not have holes in your table:
math.randomseed(os.time()) -- so that the results are always different
function FYShuffle( tInput )
local tReturn = {}
for i = #tInput, 1, -1 do
local j = math.random(i)
tInput[i], tInput[j] = tInput[j], tInput[i]
table.insert(tReturn, tInput[i])
end
return tReturn
end

Return strings from table values Lua

I am trying to learn how to print strings from a value in a table. For example.
TestTable = { "Apples" = 0, "Oranges" = 1, "Grapes" = 1, "Bananas" = 0}
for i=1, #TestTable do
if TestTable[i] == 1 then
print(TestTable[i]) --> Oranges Grapes
end
end
Not sure if that made sense, but I want to print all the strings with the 1 value.
Unless the __len metamethod is defined, the # operator can only be used on a sequence, but TestTable is not one.
You can use pairs to iterate the table:
TestTable = { Apples = 0, Oranges = 1, Grapes = 1, Bananas = 0}
for k, v in pairs(TestTable) do
if v == 1 then
print(k)
end
end

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