Sets

Search for an item in a list

There’s no built in way to search a list for a particular item. However Programming in Lua shows how you might build a set that can help:

function Set (list)
  local set = {}
  for _, l in ipairs(list) do set[l] = true end
  return set
end

Then you can put your list in the Set and test for membership:

local items = Set { "apple", "orange", "pear", "banana" }

if items["orange"] then
  -- do something
end

Using a Table as a Set

Create a set

 local set = {} -- empty set

Create a set with elements by setting their value to true:

 local set = {pear=true, plum=true}

 -- or initialize by adding the value of a variable:
 local fruit = 'orange'
 local other_set = {[fruit] = true} -- adds 'orange'

Add a member to the set

add a member by setting its value to true

  set.peach = true
  set.apple = true
  -- alternatively
  set['banana'] = true
  set['strawberry'] = true

Remove a member from the set

  set.apple = nil

Using nil instead of false to remove ‘apple’ from the table is preferable because it will make iterating elements simpler. nil deletes the entry from the table while setting to false changes its value.

Membership Test

  if set.strawberry then
      print "We've got strawberries"
  end

Iterate over elements in a set

 for element in pairs(set) do
     print(element)
 end