8/23/2019 Lua Table Insert
I have a table of strings. I'd like an easy way to remove all of the duplicates of the table.
So if the table is
{a, b, c, c, d, e, e} , after this operation it would be {a, b, c, d, e}
Alternatively, and probably preferably, is there a way to add an element to a table, but only if it is not already contained within the table.
Jul 05, 2014 The function call you tried is t:insert(9) So the syntax rule you stated would be t.insert(t, 9) But the working function call is table.insert(t, 9) See how the last two aren't the same? So the answer to your question is that insert isn't a function contained in t, it's in 'table'. Void table.insert ( array t, Variant value ). Will be true after the sort). If comp is not given, then the standard Lua operator less than is used instead.
<noobquestion>
Colton PhillipsColton Phillips
3 Answers
What I normally do for this is index the table on the string so for example
etc.
When you add a string you simply use the lines above and duplicates will be taken care of. You can then use a for ... pairs do loop to read the data.
If you want to count the number of occurrences
use something like
As the end of the addition cycle if you need to turn the table around you can simply use something like
![]()
Jane TJane T
It sounds like you're trying to implement a Set, a collection of unique elements. This article might help you: http://www.lua.org/pil/13.1.html
2rs2ts2rs2ts
The simplest way is using the tables as keys, not as values, in your 'container table'.
Let's call the container table
values . You must currently be doing something similar to this for adding elements to it:
And you parse
values like this:
In order to have the tables just once, you can insert them this other way:
This will ensure that the inserted values (strings, tables, numbers, whatever) are included just once, because they will be 'overwritten'.
Then you can parse
t like this:
kikitokikito
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For simple data operations, we may use files, but, sometimes, these file operations may not be efficient, scalable, and powerful. For this purpose, we may often switch to using databases. LuaSQL is a simple interface from Lua to a number of database management systems. LuaSQL is the library, which provides support for different types of SQL. This include,
In this tutorial, we will be covering database handling of MySQL an SQLite in Lua. This uses a generic interface for both and should be possible to port this implementation to other types of databases as well. First let see how you can do the operations in MySQL.
MySQL db Setup
In order to use the following examples to work as expected, we need the initial db setup. The assumptions are listed below.
Importing MySQL
We can use a simple require statement to import the sqlite library assuming that your Lua implementation was done correctly.
The variable mysql will provide access to the functions by referring to the main mysql table.
Setting up Connection
We can set up the connection by initiating a MySQL environment and then creating a connection for the environment. It is shown below.
The above connection will connect to an existing MySQL file and establishes the connection with the newly created file.
Execute Function
There is a simple execute function available with the connection that will help us to do all the db operations from create, insert, delete, update and so on. The syntax is shown below −
In the above syntax, we need to ensure that conn is open and existing MySQL connection and replace the 'MySQLSTATEMENT' with the correct statement.
Create Table Example
A simple create table example is shown below. It creates a table with two parameters id of type integer and name of type varchar.
When you run the above program, a table named sample will be created with two columns namely, id and name.
In case there is any error, you would be returned an error statement instead of nil. A simple error statement is shown below.
Insert Statement Example
An insert statement for MySQL is shown below.
Update Statement Example
An update statement for MySQL is shown below.
Delete Statement Example
A delete statement for MySQL is shown below.
Select Statement Example
As far as select statement is concerned, we need to loop through each of the rows and extract the required data. A simple select statement is shown below.
In the above code, conn is an open MySQL connection. With the help of the cursor returned by the execute statement, you can loop through the table response and fetch the required select data.
A Complete Example
A complete example including all the above statements is given below.
When you run the above program, you will get the following output.
Performing Transactions
Transactions are a mechanism that ensures data consistency. Transactions should have the following four properties −
Transaction starts with START TRANSACTION; and ends with commit or rollback statement.
Start Transaction
In order to initiate a transaction, we need to execute the following statement in Lua, assuming conn is an open MySQL connection.
Rollback Transaction
We need to execute the following statement to rollback changes made after start transaction is executed.
Commit Transaction
We need to execute the following statement to commit changes made after start transaction is executed.
We have known about MySQL in the above and following section explains about basic SQL operations. Remember transactions, though not explained again for SQLite3 but the same statements should work for SQLite3 as well.
Importing SQLite
We can use a simple require statement to import the SQLite library assuming that your Lua implementation was done correctly. During installation, a folder libsql that contains the database related files.
The variable sqlite3 will provide access to the functions by referring to the main sqlite3 table.
Setting Up Connection
We can set up the connection by initiating an SQLite environment and then creating a connection for the environment. It is shown below.
The above connection will connect to an existing SQLite file or creates a new SQLite file and establishes the connection with the newly created file.
Execute Function
There is a simple execute function available with the connection that will help us to do all the db operations from create, insert, delete, update and so on. The syntax is shown below −
In the above syntax we need to ensure that conn is open and existing sqlite3 connection and replace the 'SQLite3STATEMENT' with the correct statement.
Create Table Example
A simple create table example is shown below. It creates a table with two parameters id of type integer and name of type varchar.
When you run the above program, a table named sample will be created with two columns namely, id and name.
In case of an error, you would be returned a error statement instead of nil. A simple error statement is shown below.
Insert Statement Example
An insert statement for SQLite is shown below.
![]() Select Statement Example
As far as select statement is concerned, we need to loop through each of the rows and extract the required data. A simple select statement is shown below.
In the above code, conn is an open sqlite3 connection. With the help of the cursor returned by the execute statement, you can loop through the table response and fetch the required select data.
A Complete Example
A complete example including all the above statements is given below.
When you run the above program, you will get the following output.
We can execute all the available queries with the help of this libsql library. So, please don't stop with these examples. Experiment various query statement available in respective MySQL, SQLite3 and other supported db in Lua.
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