CODEWITHSUNDEEP
lua
Phenrila
Phenrila

Reputation: 1

lua - how to compare different array

im trying to compare 2 arrays but i dont know how

for example:

local array1 = { 'friend', 'work', 'privat' }
local array2 = { 'apple', 'juice', 'privat' }

if both arrays have the same value it should do a print.

i know i need to work with something like this

for x in ipairs(array1) do
    if x == array2 then
        print ("Hi")
    end
end

but ofcourse it didnt work. so how can i check if the array1 value contains a values from array2?

Upvotes: 0

Views: 1833

Answers (3)

luther
luther

Reputation: 5544

(I'm writing a second answer to account for another possible interpretation of the question.)

If you want to see if array1 contains any value that's also in array2, you can do the following:

  1. Convert array1 to a set. A set is a new table where the array's values become keys whose values are true.
  2. Iterate through array2 to see if any of its values are a key in the set.
local set = {}
for _, v in ipairs(array1) do
  set[v] = true
end

for _, v in ipairs(array2) do
  if set[v] then
    print'Hi'
    -- Use a break statement if you only want to say hi once.
  end
end

If the arrays are large, this algorithm should be faster than a nested loop that compares every value in array1 to every value in array2.

Upvotes: 0

Toast
Toast

Reputation: 13

how can i check if the array1 value contains a values from array2?

@luther's answer will not always work for your question..

If the arrays are different sizes, it completely fails.

If you have an array where similar element are not in the exact same index, it can return a false negative.

  • for example a = {'one', 'two'}; b = {'two', 'one'} will return false

Using table.sort to solve this would be a band-aid solution without fixing the real problem.

The function below will work with arrays of different sizes containing elements in any order

function array_compare(a, b)
  for ia, va in ipairs(a) do 
    for ib, vb in ipairs(b) do 
      if va == vb then 
        print("matching:",va)
      end
    end
  end
end

In array_compare we go through all the combinations of elements in table a and table b, compare them, and print if they are equal.

ipairs(table) uses index, value (instead of just value)

For example

local array1 = { 'friend', 'work', 'privat' }
local array2 = { 'apple', 'juice', 'privat' }
array_compare(array1, array2)

will print

matching: privat

Upvotes: 0

luther
luther

Reputation: 5544

Think of it this way: You have to check each element in the first array to its counterpart in the second. If any element is not equal, you know right away that the arrays aren't equal. If every element checks out as equal, the arrays are equal.

local function arrayEqual(a1, a2)
  -- Check length, or else the loop isn't valid.
  if #a1 ~= #a2 then
    return false
  end

  -- Check each element.
  for i, v in ipairs(a1) do
    if v ~= a2[i] then
      return false
    end
  end
  
  -- We've checked everything.
  return true
end

Upvotes: 3

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