If you are used to other languages, then obj. To make a proper method call, use obj:method which is 'syntactical sugar' for obj. Common methods encountered in basic Lua programming are the string methods, like s:find "hello" being short for string. C-like languages regard 0 as equivalent to falsebut this is not true for Lua. Only an explicit false or nil are equivalent to false. When in doubt, make the condition explicit, e.
Like all dynamic languages, you don't have to declare variables. However, the scope of what gets implicitly declared is not the same. For instance, an undeclared variable is local to the function in Python, and you need the keyword global to tell the interpreter to look outside. Also, the value of an undeclared variable is nilbecause there is no special undefined value. Since nil may be an acceptable value for a variable, typing errors can bite deep.
This also works in Python:. But don't expect equality to work always for floating-point values! This is more a general programming gotcha, since you must become used to finite precision. Lua can be compiled only to use integer arithmetic on embedded platforms that lack hardware floating-point support. In an arithmetic expression, Lua will attempt to convert strings to numbers, otherwise you will get a 'attempt to perform arithmetic on a string value'.
The value is in the table, but is in the 'hash' or 'dictionary' part. The length operator only applies from 1 to the last non- nil element. The 'key' in t.
This is because t. If you want to index by a variable, say t[key].By cantulandMay 10, in Building Wherigo Cartridges. Lua doesn't really have arrays, it has tables. This is imprtant since the index values can be anything, not just integers. Seems to have worked fine for everything I've done so far. You can post now and register later. If you have an account, sign in now to post with your account. Note: Your post will require moderator approval before it will be visible.
Paste as plain text instead. Only 75 emoji are allowed. Display as a link instead. Clear editor. Upload or insert images from URL. Building Wherigo Cartridges Search In. Lua call for array size? Reply to this topic Start new topic. Recommended Posts. Posted May 10, Is there a Lua Language call that can be used to find the number of items in an array?
I just would like to know the variable for the length of an array. Posted 03 September - AM An array in lua is actually called a table. You can find the length of a table via the hash symbol: So if I wanted to find the length of table "t", i would do " t". Posted 03 September - AM watch out though, that is bugged, it only counts values if they are defined by consecutive numbers starting at 1.
Posted 03 September - AM It's not a bug, lol. It's only supposed to count number indexes.
There are also two ways of specifying the keys to make things even more fun. The operator will not work with the key-value style of tables, it only works with numeric indexed arrays. If you use tablename and the count is less than you expect, you likely have a nil in the table.
The API function: table. Keep in mind this also only works on numerically indexed tables, not the key-value type. Product Corona Support CoronaCards. Stories Hall of Fame. About Jobs Roadmap Contact. Copyright Corona Labs Inc. All rights reserved.Tables are the only data structure available in Lua that helps us create different types like arrays and dictionaries.
Lua uses associative arrays and which can be indexed with not only numbers but also with strings except nil. Tables have no fixed size and can grow based on our need. Lua uses tables in all representations including representation of packages. When we access a method string.
Tables are called objects and they are neither values nor variables. It is to be known that there is no fixed relationship between a variable that holds reference of table and the table itself. When we have a table a with set of elements and if we assign it to bboth a and b refer to the same memory.
No separate memory is allocated separately for b. When a is set to nil, table will be still accessible to b. When there are no reference to a table, then garbage collection in Lua takes care of cleaning up process to make these unreferenced memory to be reused again.
Insertion and removal of items in tables is most common in table manipulation. It is explained below. We often require to sort a table in a particular order. The sort functions sort the elements in a table alphabetically. A sample for this is shown below. Lua - Tables Advertisements. Previous Page. Next Page. Live Demo. Previous Page Print Page. See example for detail.I was wondering what is the advantage in not enforcing a table without an array part to return a len of 0.
I would have found more intuitive considering only strictly positive integers, i. Sorry about the noise on the second part of my post, at least for 5. Search everywhere only in this topic. Advanced Search. Classic List Threaded. Lua 5. Hello, I'm trying to reconcile documentation to the surprising behavior of the length operator on a table.
But in any case, I'd expect defined behavior rather than undefined behavior. I can not wrap my head around how the above behavior might be defined. Smells like a bug to me. The other bit of strangeness represented above of setting a value of non numerical index having interaction with the length operator seems to go against documentation also, but that is likely just some internal implementation details leaking out by the existence of the previous issue. For a further related? Sometimes the unpack list contains the same nil parameters, others not.How to determine or get array length (size) in C/C++
Dirk Laurie Re: Lua 5. Matthew Wild. In reply to this post by Chris Rempel. In that case, n is its length. It might be surprising, until you read the documentation. Re-read the first sentence of the documentation you linked, especially the words "is only defined if". That means you cannot rely on it to give any particular value. It's not defined to be random either though, so don't use it for a random number generator : Dirk is right, this issue has been brought up many times - if you're interested in the background, reading the mailing list archives should be fairly educational.
I answered your post in full mainly because it's the first question I've seen about 5. Regards, Matthew.
Is this the correct way to initialize an array in LUA?
Jose Torre-Bueno. In reply to this post by Dirk Laurie Attempting to define explicitly undefined behaviour is just not a good idea. It will easily lead you down the road of portability and compatibility problems.
Petite Abeille. Krunal Rao. In reply to this post by Jose Torre-Bueno. Honest question, not a critique. For a regular array, with non-nil values from 1 to a given n, its length is exactly that n, the index of its last value.
If the array has "holes" that is, nil values between other non-nil valuesthen t CAN be any of the indices that directly precedes a nil value that is, it may consider any such nil value as the end of the array " With emphasis on the CAN added. My interpretation is that this is a reflection of the Lua parser's method of storing a table internally as two objects; a regular array of some optimum size that is a power of two and some sort of hashed list.
Am I correct that is the size of the array part of a table? Clearly it cannot be used to figure out what ipairs might do. Is there any way other than probing as Carl did to find out how Lua has organized a table or even to predict what ipairs will do?Being the most widely used language for statistical computing, R features a huge number of scientific libraries.
Of particular relevance is the possibility to leverage on the plotting capabilities of ggplot2 and similar libraries:. The following R code, to be executed in a R session, installs Rserve and starts a local R session:. In R almost every data structure is based on a R vector also called generic vector. Conceptually a R vector is a sequence of elements of arbitrary type including other R vectors. We say that a R object is atomic if it cannot be further decomposed into finer data structures.
The following table lists the correspondences between R atomic type names and Lua type names:. We say that a R object is a R array if it is a R vector and and all its elements are atomics of the same type. A R scalar is a R array of length 1. R objects can have associated attributes which store metadata information. A R matrix is a R array with an attribute identifying the dimensions. A R list is a R vector of R vectors with an attribute identifying the column names.
A R data. This library allows the exchange between Lua and R of the following R aggregate types:. NOTE: no nesting is allowed for any of the R aggregate types for instance a list of lists is not supported. This last data structure is the one that corresponds to a R array. Whenever a Lua array is expected a Lua scalar corresponding to a R atomic can be passed instead and this is equivalent to passing a Lua array of length 1.
Objects are transfered from Lua to R via set-variable statements. The Lua object on the right hand side must be either nilor a Lua array, or the object returned by one of the following functions: asmatrixaslistasdataframe. Objects are transfered from R to Lua via get-variable statements.
The R object being indexed on the left hand side must be either a R atomic or a not nested R aggregate. A Lua table is always returned unless the R object is nullin which case nil is returned whose structure depends on the R type. The cases of R arrays and R matrices behave as expected: a Lua array or a Lua table array of Lua arrays is returned. Remember that R scalars really are R arrays of length 1.
Opens a connection to an instance of R started by Rserve and returns a connection object. The defaults result in a connection to a local instance of R started by Rserve in its default configuration. Executes the string rcode and and passes the last result if present in string form to out.
As out defaults to print this function mimics the R interpreter by default. Returns an object which is interpreted on R side as a R matrix. The input x must be a Lua table array of Lua arrays sharing the same length and element type.
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