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For example: - Create a table to store the types of pets we like.
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Avoiding gaps in tables used as arrays Defining our termsīy array here we mean a Lua table used as a sequence. It uses the table.insert() to append the randomly extracted element onto the end of same table, and the table.remove() to randomly extract an element from the remaining unshuffled portion of the table. It implements the Fisher-Yates Shuffle, perhaps inefficiently. Table.insert(t, table.remove(t, math.random(#t-i)))
#LUA TABLE INSERT AND REMOVE CODE#
Leveraging that, you can write code like the example below. As you might be able to tell the second method of calling table.insert() and table.remove() provides stack semantics to tables. These two functions mutate the given table. Creating tablesĬreating an empty table is as simple as this: local empty_table =, r = "e" When coding for a table with a sequence, it is important to avoid breaking the sequence Only remove the last element or use a function, like the standard table.remove, that shifts elements down to close the gap.
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Iterators would no longer see the related key. Setting a value in a table to nil removes it from the table. Certain standard operations and functions only work on the sequence of a table and some have non-deterministic behavior when applied to a table without a sequence. Other languages call this a 1-based array. The key-value pairs with positive integer keys are the elements of the sequence. So, for example, one table could contain strings, functions, booleans, numbers, and even other tables as values or keys.Ī Lua table with consecutive positive integer keys beginning with 1 is said to have a sequence. The items contained in a table can be a mixture of Lua types. Lua does not enforce any particular rules on how tables are used. Finally, tables can be used to build classes in Lua and to create a module system. Many structural patterns can be built with tables: stacks, queues, sets, lists, graphs, etc. As such, a Lua table can resemble a dictionary, hashmap or associative array from other languages. This is either elegant simplicity or confusing, depending on how you look at it.Ī Lua table is a collection of key-value pairs where the keys are unique and neither the key nor the value is nil. Note that table.remove only works with numeric indexes.Tables are the only built-in data structure available in Lua. > table.foreach(t, print) - display elements > = table.remove(t) - remove last element > table.foreach(t, print) - display table contents, note size "n" is stored internally If the size of the table does not reflect the number of elements nothing is removed, e.g., > table.foreach(t, print) - display updated contents > = table.remove(t) - remove the element at position "n" > table.foreach(t, print) - display contents > = # t - find the table size (which is removed) If no position is given remove the last element in the table which is specified by the size of the table. > table.foreach(t, print) - display the updated table contents > = table.remove(t,2) - remove element number 2 and display it > table.foreach(t, print) - have a look at the elements Additionally a range can be specified within the table, starting at the i-th element and finishing at the j-th element. A separator can be specified which is placed between concatenated elements. Each element must be able to be coerced into a string. Ĭoncatenate the elements of a table to form a string. For these functions, when we talk about the "length" of a table we mean the result of the length operator. We'll quote it here: Most functions in the table library assume that the table represents an array or a list.
#LUA TABLE INSERT AND REMOVE MANUAL#
The manual is concise about the purpose of this library. There are more details about tables in the TablesTutorial. The table library is explained in section 5.5 of the Reference Manual. Lua-users wiki: Table Library Tutorial Table Library Tutorial